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H1
ken shirriff's blog
H2
why op amps are important
transistors inside the ic
how the op amp works
interactive chip viewer
how i photographed the op amp die
some strange things in the lm108 die
conclusion
notes and references
how rfid timing works
inside the chip
these chips are really small
the antenna
conclusion
using contralto
smalltalk
writing bcpl code
the diagnostics disk
the contralto debugger
conclusion
incompatibility in the alto's circuit boards
some alto software
the mouse
conclusion
notes and references
microcode
the bank switch hardware
conclusion
popular posts
labels
power supply posts
blog archive
quick links
H3
superbeta transistors inside: die photos and analysis of the lm108 op amp
the differential pair
the lm108 op amp circuit
ic component: the current mirror
inside a rfid race timing chip: die photos of the monza r6
simulating a xerox alto with the contralto simulator: games and smalltalk
restoring yc's xerox alto day 10: new boards, running programs, mouse problems
restoring yc's xerox alto day 9: tracing a crash through software and hardware
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Linki zewnętrzne

superbeta transistors inside: die photos and analysis of the lm108 op amp http://www.righto.com/2016/12/inside-lm108-op-amp-superbeta.html
741 op amp http://www.righto.com/2015/10/inside-ubiquitous-741-op-amp-circuits.html
bob widlar https://en.wikipedia.org/wiki/bob_widlar
- https://lh3.googleusercontent.com/-kvve3bl2uxg/wd26muosrei/aaaaaaaa-ng/fnnfdmoogbki5fc9tnshqbbjrl7a-txowchm/s9999/lm308-package.jpg
doping http://www.halbleiter.org/en/fundamentals/doping/
- https://lh3.googleusercontent.com/-y0z_cfx79_w/wd26myjhc1i/aaaaaaaa-os/hif6xazjp5kvnd_ndgntcqyrnqotxwvugchm/s9999/die.jpg
- https://picasaweb.google.com/lh/photo/vwmi0jrilua2szic-yepmrje37q18ofd30djrlgrmeu
- https://picasaweb.google.com/lh/photo/yqvcdsjnyxo1rryjovddxqxgdqamjcnfmpu6osocz2k
741 http://www.righto.com/2015/10/inside-ubiquitous-741-op-amp-circuits.html
- https://lh3.googleusercontent.com/-z2plzojjwsq/wd59wsvcpbi/aaaaaaaa-qy/gjvrwybwanwx5t7tooatldenaftipgppachm/s9999/supertransistor.jpg
- https://lh3.googleusercontent.com/-ozchfvtnesu/vsjxhibg8ji/aaaaaaaazge/_4ws_u40ag4/s9999/differential-pair.png
- https://lh3.googleusercontent.com/-x9rmgyjxp9c/wd28_rbpyti/aaaaaaaa-pa/zd3gyhxiiiamj7zimm-lfljvj6wo1jz_wchm/s9999/lm108-classic-simplified.png
class ab https://en.wikipedia.org/wiki/amplifier#class_ab
- https://lh3.googleusercontent.com/-m9ffpys6u6y/wd293i58fbi/aaaaaaaa-ps/jez2tynmxqsr8pelyzapqlnrlicvo9ukwchm/s9999/lm108-current-source.png
- https://picasaweb.google.com/lh/photo/7n5mrq84xrgktbteouv3xqxgdqamjcnfmpu6osocz2k
patented https://patents.google.com/patent/us3930172a/en
- https://lh3.googleusercontent.com/-lu0dhgsafdo/wd597u8f-wi/aaaaaaaa-q0/-cn-u1j_ejkwho-uninwcj7xqskhrcc6qchm/s9999/current-source-labeled.png
concentrated acid http://zeptobars.ru/en/read/how-to-open-microchip-asic-what-inside
metallurgical microscope http://www.amazon.com/gp/product/b004wmfoy4/ref=as_li_tl?ie=utf8&camp=1789&creative=390957&creativeasin=b004wmfoy4&linkcode=as2&tag=rightocom&linkid=mnrlkeiwaybrwva6
details http://www.righto.com/2015/12/creating-high-resolution-integrated.html
- https://lh3.googleusercontent.com/-azxhq4oaqqi/wd26mffrjti/aaaaaaaa-os/9ottcf12ovszoszdmql2wglf2qspfvc1wchm/s9999/lm308-package-opened.jpg
741 op amp http://www.righto.com/2015/10/inside-ubiquitous-741-op-amp-circuits.html
- https://picasaweb.google.com/lh/photo/cgjd92ou_t_i589zio2slaxgdqamjcnfmpu6osocz2k
- https://lh3.googleusercontent.com/-brkmx2x46zo/wd59wu0cvki/aaaaaaaa-qs/r4b2y7q9gpux7mjab33fhwcizm-ibzwuqchm/s9999/unused.jpg
- https://lh3.googleusercontent.com/-fz4g9ccnsze/wd59wmri-bi/aaaaaaaa-qy/ptjznj2g4qyzhbgxjoy1s5npglhazofpqchm/s9999/resistor.jpg
- https://lh3.googleusercontent.com/-7ikx7uzl0si/webhv72eedi/aaaaaaaa-tg/cnjtvwku5jwfc_eghpbakm8g25qxrto6gchm/s9999/double-transistor.png
- https://lh3.googleusercontent.com/-4qppunxklz4/wd-m9pjwp4i/aaaaaaaa-sk/cj588b4mmxgdvjkbpie_u44ym03nhbwcqchm/s9999/frankenchip.png
bil herd https://en.wikipedia.org/wiki/bil_herd
/r/askelectronics https://www.reddit.com/r/askelectronics/comments/5e1gqe/how_does_transistor_with_double_basesemitters/
kenshirriff https://twitter.com/kenshirriff
widlar current source https://en.wikipedia.org/wiki/widlar_current_source
here http://electronicdesign.com/analog/what-s-all-widlar-stuff-anyhow
pictures of his sheep http://readingjimwilliams.blogspot.com/2011/08/app-note-16-and-sheep.html
input bias current http://www.analog.com/media/en/training-seminars/tutorials/mt-038.pdf?doc=cn0326.pdf
application note http://pe2bz.philpem.me.uk/parts-active/ic-analog/-%20an-national/an-29-opamp-beatsfet-oninputcurrent.pdf
temperature range https://en.wikipedia.org/wiki/list_of_lm-series_integrated_circuits#notes
motorola lm108 http://www.datasheets360.com/pdf/3369391827646776302
national semiconductor http://www.mit.edu/~6.301/lm108.pdf
datasheet http://www.datasheets360.com/pdf/6368862147977573577
distortion pedals https://en.wikipedia.org/wiki/pro_co_rat#circuitry
op amp circuit collection http://electro.uv.es/asignaturas/ea2/archivos/an-31.pdf
op amp applications handbook https://www.amazon.com/gp/product/0750678445/ref=as_li_tl?ie=utf8&camp=1789&creative=9325&creativeasin=0750678445&linkcode=as2&tag=rightocom&linkid=f11703c2738306ea83dffd8c271cf43c
pdf http://www.analog.com/en/education/education-library/op-amp-applications-handbook.html
ic op-amps through the ages http://www.ee.bgu.ac.il/~angcirc/history/solutions_2003_2004_b/somestuff/history18opamp.pdf
op amp history http://www.analog.com/media/en/training-seminars/design-handbooks/op-amp-applications/sectionh.pdf
here http://protorit.blogspot.com/2011/11/ad741-precision-741.html
analysis and design of analog integrated circuits http://www.amazon.com/gp/product/0470245999/ref=as_li_tl?ie=utf8&camp=1789&creative=390957&creativeasin=0470245999&linkcode=as2&tag=rightocom&linkid=m7y4igg5inyyfpew
wikipedia http://en.wikipedia.org/wiki/differential_amplifier#long-tailed_pair
pdf version http://www.designinganalogchips.com/_count/designinganalogchips.pdf
ic op amp beats fets on input current http://pe2bz.philpem.me.uk/parts-active/ic-analog/-%20an-national/an-29-opamp-beatsfet-oninputcurrent.pdf
wikipedia http://en.wikipedia.org/wiki/current_mirror
designing analog chips http://www.designinganalogchips.com/_count/designinganalogchips.pdf
bandgap voltage reference http://www.righto.com/2014/09/reverse-engineering-counterfeit-7805.html
patent 3930172 https://patents.google.com/patent/us3930172a/en
reducing dc errors in op amps https://archive.org/stream/nationalsemiconductorlinearapplicationshandbook1994#page/n541/mode/2up
zener zapping https://en.wikipedia.org/wiki/antifuse#zener_antifuses
- https://lh3.googleusercontent.com/-dbbgr3qi0qe/wd27gksvpmi/aaaaaaaa-os/fodfhbrkj-4_suhpteea0-c4ooefklkngchm/s9999/strange-transistors.png
/r/askelectronics https://www.reddit.com/r/askelectronics/comments/5e1gqe/how_does_transistor_with_double_basesemitters/
- https://lh3.googleusercontent.com/-hevhxalc4uk/wd28xzq_-ai/aaaaaaaa-pa/iy0q_bi14ceo0shv6zq0fdg-m8ik58sqwchm/s9999/strange-transistors-schematic.png
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electronics http://www.righto.com/search/label/electronics
reverse-engineering http://www.righto.com/search/label/reverse-engineering
inside a rfid race timing chip: die photos of the monza r6 http://www.righto.com/2016/10/inside-rfid-race-timing-chip-die-photos.html
- https://lh3.googleusercontent.com/-bojd5tyga50/wa2cs7vc1xi/aaaaaaaa9ss/ypbxr-ivxmch0cstjfvivpufeci8ze4zachm/s9999/bib.jpg
metallurgical microscope http://www.amazon.com/gp/product/b004wmfoy4/ref=as_li_tl?ie=utf8&camp=1789&creative=390957&creativeasin=b004wmfoy4&linkcode=as2&tag=rightocom&linkid=mnrlkeiwaybrwva6
adhesive https://www.delo-adhesives.com/us/applications/flip-chip-bonding/
this article http://www.righto.com/2015/12/creating-high-resolution-integrated.html
- https://lh3.googleusercontent.com/-f6hw6eay0-o/wa2cs3sje6i/aaaaaaaa9so/zls_olohcvcuwu_nwv1mizppl3xxqnx8gchm/s9999/monza6-die.jpg
impinj http://impinj.com
datasheet https://support.impinj.com/hc/en-us/articles/202765328-monza-r6-product-datasheet
- https://lh3.googleusercontent.com/-x87xhjwv828/wa2cs2fq6ti/aaaaaaaa9so/gek6-u-9gd8jubyh2cicsaalhozsi9wqgchm/s9999/monza6-datasheet.png
epc standard http://www.gs1.org/sites/default/files/docs/epc/uhfc1g2_2_0_0_standard_20131101.pdf
epc http://www.gs1.org/sites/default/files/docs/epc/tds_1_9_standard.pdf
details http://blog.atlasrfidstore.com/uhf-rfid-tag-communications-protocols-standards
backscatter http://ww1.microchip.com/downloads/en/appnotes/00680b.pdf
anti-collision protocol http://www.rfidjournal.com/blogs/experts/entry?9271
aloha https://en.wikipedia.org/wiki/alohanet#slotted_aloha
- https://lh3.googleusercontent.com/-lnzgtnpmd8o/wa2cs10b5-i/aaaaaaaa9so/rdqgwedcec82fejgx2spz7gcgoikuxlhgchm/s9999/monza6.png
patent https://www.google.com/patents/us7561866
charge pump https://en.wikipedia.org/wiki/charge_pump
city https://en.wikipedia.org/wiki/kelso,_washington
this impinj patent https://www.google.com/patents/us7561866
wrote about http://www.righto.com/2016/06/inside-tiny-rfid-chip-that-runs-san.html
- https://lh3.googleusercontent.com/-2wkkt_-qqwc/v2zaoahcgfi/aaaaaaaa4du/kfpbris2sbekzw1e59irfdz_imjiqv2jqchm/s9999/chip-0008.png
- https://lh3.googleusercontent.com/-fhxjiao1dh8/wa6r3uhs_vi/aaaaaaaa9t0/bkhd0zppi-yotxai7xal4lujt7ad8hyvgchm/s9999/antenna-labeled.png
application note http://www.nxp.com/documents/application_note/an162910.pdf
smartrac https://www.smartrac-group.com/files/content/products_services/pdf/smartrac_dogbone_impinj_monza_r6.pdf
13 cents https://www.atlasrfidstore.com/smartrac-r6-dogbone-rfid-wet-inlay-monza-r6/
full size http://blog.atlasrfidstore.com/near-field-communication-infographic/
- http://blog.atlasrfidstore.com/rfid-vs-nfc
atlasrfidstore http://blog.atlasrfidstore.com/near-field-communication-infographic/
kenshirriff https://twitter.com/kenshirriff
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electronics http://www.righto.com/search/label/electronics
reverse-engineering http://www.righto.com/search/label/reverse-engineering
simulating a xerox alto with the contralto simulator: games and smalltalk http://www.righto.com/2016/10/simulating-xerox-alto-with-contralto.html
contralto http://www.livingcomputermuseum.org/online-systems/press.aspx
y combinator https://blog.ycombinator.com/harc
marc verdiell https://www.youtube.com/user/mverdiell
carl claunch http://rescue1130.blogspot.com/
ed thelen http://ed-thelen.org/
zip file http://www.livingcomputermuseum.org/online-systems/contraltosetup.aspx
bitsavers.org http://www.bitsavers.org/bits/xerox/alto/disk_images/
- https://lh3.googleusercontent.com/-j0mbnvusgxq/v9ohps_iq2i/aaaaaaaa8zw/v4c214euvaaauahw8cxldvabkc7xznrygchm/s9999/inserting-disk.jpg
readme file https://github.com/livingcomputermuseum/contralto/tree/master/contralto
- https://lh3.googleusercontent.com/-r2rtnvbzz_u/wamwdr_z0hi/aaaaaaaa9o8/fszdd4a5iy0a_fujd4zjacnkjredyitmgchm/s9999/directory.png
- https://lh3.googleusercontent.com/-gmpir2069-g/wamwdtn-gqi/aaaaaaaa9o8/cf0omnvrsgigog9cy6lsxiuqgxjduucswchm/s9999/invaders.png
trek https://en.wikipedia.org/wiki/alto_trek
- https://lh3.googleusercontent.com/-mbw6axeximy/wamweqqdp4i/aaaaaaaa9o8/nagpuq5g0hkr5dmfcicyi2b1cqrduukwachm/s9999/spacewar.png
dealers of lightning http://amzn.to/2edl9wq
st80.dsk http://bitsavers.trailing-edge.com/bits/xerox/alto/disk_images/st80.dsk
xmsmall.zip http://www.mirrorservice.org/sites/www.bitsavers.org/bits/xerox/alto/disk_images/chm/xmsmall.zip
- https://lh3.googleusercontent.com/-u5eio5mdpsw/wamwenptzwi/aaaaaaaa9o8/ve1d5jgxvqyejkg1db-givvuymlgvpwqwchm/s9999/smalltalk2.png
reflection https://en.wikipedia.org/wiki/smalltalk#reflection
this document http://xeroxalto.computerhistory.org/filene/smalltalk-76/.document.press!1.pdf
- https://lh3.googleusercontent.com/-cxds-co6ug4/warcajday7i/aaaaaaaa9pw/yn9awpunw74fawemm8ff1fpyl0qwfmxmachm/s9999/bitrect.png
tdisk4.dsk.z http://bitsavers.org/bits/xerox/alto/simulator/salto/disks/tdisk4.dsk.ztdisk4.dsk.z
article earlier http://www.righto.com/2016/06/hello-world-in-bcpl-language-on-xerox.html
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diags.zip http://www.mirrorservice.org/sites/www.bitsavers.org/bits/xerox/alto/disk_images/chm/diags.zip
blog posts http://www.righto.com/search/label/alto
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living computer museum http://www.livingcomputermuseum.org/
kenshirriff https://twitter.com/kenshirriff
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restoring yc's xerox alto day 10: new boards, running programs, mouse problems http://www.righto.com/2016/10/restoring-ycs-xerox-alto-day-10-new.html
traced the problem http://www.righto.com/2016/10/restoring-ycs-xerox-alto-day-9-tracing.html
y combinator https://blog.ycombinator.com/harc
marc verdiell https://www.youtube.com/user/mverdiell
carl claunch http://rescue1130.blogspot.com/
ed thelen http://ed-thelen.org/
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bitsavers http://bitsavers.org
- https://lh3.googleusercontent.com/-ikne2ted_38/waf3a8tkivi/aaaaaaaa9z8/v0qzih2rhbk-lvk3cwhsfwkphjpbthzzgchm/s9999/ctrl3k.jpg
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here http://www.righto.com/2016/06/hello-world-in-bcpl-language-on-xerox.html
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prepress http://xeroxalto.computerhistory.org/_cd8_/altodocs/.prepress.press!2.pdf
fred https://www.questia.com/library/journal/1p3-4201408091/the-xerox-alto-font-design-system
- https://lh3.googleusercontent.com/-xkk0gsgwvca/waf3a7ggrzi/aaaaaaaa9z8/xiogp81jezg4s6pfmcm23mazj7z3aoumachm/s9999/prepress.jpg
contralto http://www.livingcomputermuseum.org/online-systems/press.aspx
- https://lh3.googleusercontent.com/-1a1kjzzd5oc/waf39qr7cyi/aaaaaaaa9ay/jtidbmzkwkglbzosbwglarcnsqwcyr3ogchm/s9999/mouse.jpg
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patented https://www.google.com/patents/us4751505
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kenshirriff https://twitter.com/kenshirriff
hardware manual http://www.mirrorservice.org/sites/www.bitsavers.org/pdf/xerox/alto/altohwref.part2.pdf
bitsavers http://bitsavers.informatik.uni-stuttgart.de/pdf/xerox/alto/schematics/
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details http://www.righto.com/2016/09/restoring-ycs-xerox-alto-day-8-it-boots.html
y combinator https://blog.ycombinator.com/harc
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carl claunch http://rescue1130.blogspot.com/
ed thelen http://ed-thelen.org/
here http://www.righto.com/search/label/alto
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stack frames https://en.wikipedia.org/wiki/call_stack#structure
data general nova http://users.rcn.com/crfriend/museum/doco/dg/nova/base-instr.html
wrote https://news.ycombinator.com/item?id=11845369
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found a bad chip http://www.righto.com/2016/09/restoring-ycombinators-xerox-alto-day-6.html
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kenshirriff https://twitter.com/kenshirriff
living computer museum http://www.livingcomputermuseum.org/
contralto http://www.livingcomputermuseum.org/online-systems/press.aspx
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ken shirriff's blog chargers, microprocessors, arduino, and whatever superbeta transistors inside: die photos and analysis of the lm108 op amp the lm108 op amp is an interesting chip to examine under a microscope because it uses special superbeta transistors for high performance. photos of the die reveal the tiny circuitry of the chip as well as unused components that make the chip more complex than necessary. surprisingly, these extra components allow the same die to be reused for two totally different chips! in this article i examine the internals of the lm108 in detail, explain how it works and reveal how the die can take on two roles. i've written about the famous 741 op amp, which came out in 1968. a year later, the improved lm108 op amp was invented by eccentric analog ic design genius bob widlar.[1] the main claim to fame of the lm108 is it uses a very small input current, orders of magnitude smaller than the 741.[2] to attain this low input current, the lm108 contains special transistors called "superbeta" transistors, with about 25 times the amplification of a regular transistor.[3] the downside is the superbeta transistors are delicate and require special circuitry to protect them from damage. the lm308 op amp in an 8-pin metal can. the photo above shows the lm108 op amp in a metal can. (the lm308 is the commercial-grade version of the lm108.[4] ) i opened up the can and photographed the die (below). the chip's metal layer is clearly visible, with thin metal traces connecting the different parts of the chip. the square bonding pads around the edge of the chip are connected by thin wires to the chip's external pins. under the metal layer, you can see the silicon that forms the basis of the chip. to form transistors and resistors, a process called doping treats regions of the silicon with elements such as phosphorus or boron. in the die photo, these regions have a slightly different color, which makes the structure of the chip visible under the metal. die photo of the lm308 op amp. the lm308 is the commercial version of the lm108. while the chip seems incomprehensible at first, close examination reveals the different components and their connections. by carefully studying the die photo, i reverse engineered the circuit for the op amp. surprisingly, this chip has an unusual circuit design, more modern than national semiconductor's "classic" lm108 design. although the package has the national semiconductor logo, the internal circuitry matches the motorola lm308 datasheet.[5] you might expect that lm108's would all be the same internally, but as with many ics, the part number doesn't indicate as much as you expect. different manufacturers have widely differing implementations of the chip, so you can't expect two chips to behave the same just because they have the same name.[6] even so, it's puzzling that a national semiconductor chip doesn't match the national semiconductor schematic. why op amps are important the function of an op amp is to take two input voltages, subtract them, multiply the difference by a huge value (100,000 or more), and output the result as a voltage. if you've studied analog circuits, op amps will be familiar to you, but otherwise this may seem like a bizarre and pointless device. how often do you need to subtract two voltages? and why would you want to amplify by such a huge factor? would amplifying a 1 volt input result in lightning shooting from the op amp? it turns out that op amps are extremely useful and versatile, making them a key component in analog circuits. with simple feedback circuits, you can use an op amp as an amplifier, a filter, integrator, differentiator, or a variety of other circuits.[7] when an op amp is in use, the voltages on the two inputs will normally be almost identical, so multiplying by the huge amplification factor yields a reasonable output of a few volts. the point of the high amplification is it improves accuracy, even if the amplification of the overall circuit is small. transistors inside the ic transistors are the key components in a chip. the lm108 op amp uses npn and pnp bipolar transistors, while many newer op amps use low-power cmos transistors instead. if you've studied electronics, you've probably seen a diagram of an npn transistor like the one below, showing the collector (c), base (b), and emitter (e) of the transistor. a transistor is usually illustrated as a sandwich of p silicon in between two symmetric layers of n silicon; the n-p-n layers make an npn transistor. but it turns out that transistors on a chip look nothing like this, and the base often isn't even in the middle! symbol and oversimplified structure of an npn transistor. the photo below shows an npn transistor on a 741 op amp die. the different brown and purple colors are regions of silicon that has been doped differently, forming n and p regions. the whitish-yellow areas are the metal layer of the chip on top of the silicon—these form the wires connecting to the collector, emitter, and base. underneath the photo is a cross-section drawing showing approximately how the transistor is constructed. there's a lot more than just the n-p-n sandwich, but if you look carefully at the vertical cross section below the 'e', you can find the n-p-n that forms the transistor. the emitter (e) wire is connected to n+ silicon. below that is a p layer connected to the base contact (b). and below that is an n+ layer connected (indirectly) to the collector (c). structure of an npn transistor in the 741 op amp the innovative feature of the lm108 is the superbeta transistor, seen below. it has a much thinner base region below the emitter. this gives the superbeta transistor a much higher beta (i.e. amplification), but makes the transistor much more delicate: just 4 volts between the collector and emitter can "punch through" the thin base and destroy the transistor. this image shows one of the superbeta transistors in the lm108 op amp. note the large, round emitter. the green rectangle below the transistor is a resistor. how the op amp works in this section, i'll give a simplified overview of how the op amp works.[8] first i'll explain the differential pair, the important circuit that subtracts and amplifies the two input voltages. the next section explains the different parts of the lm108 op amp. the final section describes the current mirror that provides precise currents to the op amp's circuits. the differential pair the key component of an op amp is the differential pair, which is the most common two-transistor subcircuit used in analog ics.[9] you may have wondered how the op amp subtracts two voltages since it's not obvious how to make a subtraction circuit. this is the job of the differential pair. schematic of a simple differential pair circuit. the current sink sends a fixed current i through the differential pair. if the two inputs are equal, the current is split equally between the two branches. otherwise, the branch with the higher input voltage gets most of the current. the schematic above shows a simple differential pair. the current sink at the bottom provides a fixed current i, which is split between the two input transistors. if the input voltages are equal, the current will be split equally into the two branches (i1 and i2). if one of the input voltages is a bit higher than the other, the corresponding transistor will conduct more current, so one branch gets more current and the other branch gets less. a small input difference is enough to direct most of the current into the "winning" branch, providing the amplification. the lm108 op amp circuit in this section, i'll give a brief explanation of the lm108 circuit, based on a detailed discussion by bob widlar, the chip's designer.[10] the schematic below is simplified to show the key features. the superbeta transistors q1 and q2 are the heart of the chip. these form the input stage, and are connected as a differential pair. resistors r1 and r2 provide the load for the two branches of the differential pair. by using superbeta transistors for the input, the lm108 achieves high performance with very low input currents. the problem with superbeta transistors is they will break down and be destroyed by a small voltage difference, just 4 volts. the lm108 uses a couple interesting circuits to protect the superbeta transistors. the first protection mechanism is the two diodes across the inputs, ensuring the voltage difference is small. (on the chip, these diodes are implemented with transistors.) the second protection mechanism is transistors q5 and q6, which ensure that the collector-emitter voltage across the superbeta transistors is essentially zero, preventing an overload. transistors q3 and q4 "bootstrap" the desired voltage from q1/q2's emitters to q5 and q6.[11] simplified schematic of the lm108 op amp from the chip's application notes.[10] the second stage of amplification is provided by pnp transistors q9 and q10. they form a second differential amplifier that amplifies the output of the first stage. instead of resistors, q15 and q16 form the load for the second stage differential amplifier. transistors q7 and q8 bias the inputs of q9 and q10 to the right level. the output of the op amp is driven by a high-current class ab amplifier with power transistors q13 and q14. that is, q13 will pull the output high and q14 will pull the output low. to ensure that the right output transistor turns on at the right time, q11 and q12 bias the output transistors (by two diode drops). ic component: the current mirror the schematic above uses a symbol that you may not be familiar with: the double circles that indicate a current source. a current source may seem like a strange concept, but it is very common in analog integrated circuits. the idea is that instead of controlling currents with resistors (which are inconveniently large and inaccurate on ics), currents are generated from a current mirror.[12] once you have one fixed current, you can use a current mirror to generate copies of this current. simple modifications can scale the current or even invert it. detail of the lm108 op amp schematic, showing the current source symbol. the diagram below shows how a current mirror is implemented.[12] a reference current passes through the transistor on the left. (in this case, the current is set by the resistor.) since both transistors have the same emitter voltage and base voltage, they source the same current, so the current on the right matches the reference current on the left. thus, the current mirror provides a mirror image on the right of the fixed current on the left. current mirror circuit. the current on the right copies the current on the left. in the lm108, the initial current is generated not by a resistor, but by a patented four-transistor circuit that depends on one transistor having 10 times the emitter area of the others. the photo below shows the transistor that combines 10 square emitters into one large emitter, as well as an unusual transmitter with two separate emitters.[13] the lm108's current source contains some interesting transistors. the transistor on the left has 10 emitters wired together, creating a transistor with an effective emitter size of 10 times normal. the transistor on the right has two separate emitters, providing two current outputs. interactive chip viewer the image and schematic[5] below are an interactive exploration of the lm108. click a component to see its location on the die and in the schematic highlighted. the box below will give an explanation of the component. the schematic below is the full schematic for the lm108; the component numbers don't match the earlier simplified schematic. click components in the image below for more information. how i photographed the op amp die usually getting the die out of an ic requires concentrated acid to dissolve the epoxy package. but some ics, such as op amps, are available in metal cans (for shielding) which can be easily opened with a hacksaw (or even better a jeweler's saw). i used a metallurgical microscope for my die photos, but you can use even a basic middle-school microscope to see many of the chip features. the photo below shows the lm108 op amp after removing the top. the tiny die is visible in the center, with thin wires connecting the die to the pins that surround it. the metal tab on the right indicates pin 8. to create the high-resolution die photo, i composited multiple photographs into one image (details). the lm308 op amp has been cut open revealing the tiny die inside. pads on the die are connected to the pins with thin bond wires. some strange things in the lm108 die the lm108 die is more complex than i expected and has some strange circuitry. if you compare the 741 op amp (below) with the lm108, you'll notice that the 741 is much simpler. part of this is the lm108 has 30 transistor versus 22 in the 741, but this small increase in components doesn't explain the large increase in the intricacy of the lm108. after examining the lm108 closely, i realized that it has many components on the die that aren't used. more investigation revealed that the lm108 die can be reused to create an entirely different op amp, the lm11![14] the manufacturer can use the same die (with a few changes to the metal wiring layer) to produce two different integrated circuits, which presumably saves them money. die photo of the 741 op amp. this chip is much simpler than the lm108. the photo below shows some of the unused components on the lm108 die. on the left are two unused transistors, including one with two emitters. next is a larger transistor. the small component is a resistor that is shorted out by the metal on top of it, making it nonfunctional. seven diodes are connected in an undulating chain, but the chain isn't connected to anything. finally, the chip has two large unused capacitors, one of which is shown below. i was puzzled by the amount of space wasted on the die for these unused components. the lm108 integrated circuit contains an unusual number of unused components. this image shows some of them: two transistors, a larger transistor, a resistor that is shorted out, a chain of diodes, and a capacitor. another puzzle on the lm108 die is it has several resistors that are made up of multiple segments. by shorting out some of these segments with the metal layer, the resistance can be tuned to a desired value.[15] the mystery is why the lm108 die has so many resistances that need to be customized. the lm108 op amp contains several resistors with resistance than can be modified by changing the metal layer. this image shows one resistor with about 20 segments. a few of the segments are shorted out with metal, reducing the resistance. another strange feature of the lm108 die is the protection transistors are unusually large and have extra unused structures (below). the transistor has two emitters: one is a regular emitter, and the second is a large, oval superbeta transistor emitter. the superbeta emitter is not wired to anything, which raises the question of why it exists. the die has other strange, unused transistors.[16] this unusual transistor from the lm108 has two emitters: one has a regular base and one has a supertransistor base. the second emitter is not connected to anything. by studying the schematics closely, i think i solved the puzzle of these strange and unused components. i determined that the lm108 i examined is a combination of the "classic" lm108 and the lm11 op amp introduced in 1980. the diagram below shows that my chip uses the input stage from the classic lm108 (blue). but the second stage (yellow) and the current source (red) matches the lm11. all chips use the same output stage (green). the lm108 i examined (bottom) is a combination of the 'classic' lm108 and the more modern lm11 op amp. it takes the input stage from the classic (blue) and the second stage (yellow) and the current source (orange) from the lm11. all three op amps use the same output stage (green). my conclusion is the die is designed so it can be used both as an lm11 and an lm108, by just making some changes to the metal layer. thus, when configured as an lm11, the chip uses the components that are unused in the lm108. the lm11 schematic shows a zener diode for protection: this is the unused chain of diodes shown earlier. the lm11 makes use of the other unused resistors, transistors, and capacitors described above. finally, the two protection transistors in my lm108 look like a combination of a regular transistor and an unused superbeta transistor. the lm11 schematic shows weird transistors that are half regular and half superbeta, an exact match for these puzzling transistors. conclusion every ic die has its own interesting puzzles and features, and the lm108 is no exception. the lm108 is an interesting chip since it uses superbeta transistors for high performance, but requires internal protective circuitry to keep the delicate transistors safe from damage. the most unusual thing about this lm108 is that the same chip die is used for both the lm108 and the lm11 op amps, just by tweaking the metal layer. while this makes the die more complex, presumably it saves money for the manufacturer. thanks to bil herd (famed designer of the commodore 128) for suggesting the lm108 as an interesting chip to examine. /r/askelectronics had an informative discussion of the lm108's strange transistors; thanks to crb3 for pointers to relevant documents. i announce my latest blog posts on twitter, so follow me at kenshirriff. notes and references [1] by all reports, robert widlar was an amazing analog engineer, as well as an alcoholic crazy guy. widlar invented key analog ic circuits such as the widlar current source as well as groundbreaking ics such as the µa702 and µa723. in 1970 he sold his stock options for a million dollars (about 6 million adjusted for inflation) and retired to mexico at 33. some entertaining stories about him are here, on wikipedia, and with pictures of his sheep. [2] the 741 has up to 1.5µa input bias current, while the lm108's maximum input bias current is orders of magnitude lower at 3na. [3] the base of a regular transistor is 0.5 to 1^micro;m thick, while a superbeta transistor has a much thinner base of 0.1 to 0.2µm. according to an application note on the lm108, the superbeta transistor has a gain of 5000, compared to 200 for a regular npn transistor. the downside is the superbeta transistors have a breakdown voltage of 4 volts, compared to 80 for regular transistors. [4] the first digit of the part number specifies the temperature range. the lm108 is the military-grade chip that can handle the widest temperature range, the lm208 is the industrial-grade chip, and the lm308 is the commercial-grade chip with the narrowest temperature range. the "h" in lm308ah indicates the metal can package. [5] the lm108 schematic that matches my die photo is from the motorola lm108 datasheet. it is strange that my chip is labeled national semiconductor but its circuit does not match the national semiconductor datasheet. instead it matches the motorola datasheet. another variant of the lm108 is the raytheon design (datasheet). this version has a totally different second stage, output stage, and current biasing. it uses many more transistors: 48 transistors including 6 superbeta devices. [6] the lm108 is used in distortion pedals; people search out this op amp to get its specific sound quality when overdriven. since different manufacturers have different internal designs for the lm108, this raises the question of whether people may unexpectedly end up with different op amps that produce different sound effects. [7] to see the variety of circuits that can be built from an op amp, see this op amp circuit collection. the book op amp applications handbook has a ton of useful information about op amp types (including the lm108), applications, and history; it is also available as a pdf. [8] ic op-amps through the ages. op amp history (walt jung) page h.52 (also here) discusses the lm108 in more detail. [9] differential pairs are also called long-tailed pairs. according to analysis and design of analog integrated circuits the differential pair is "perhaps the most widely used two-transistor subcircuits in monolithic analog circuits." (p214) for more information about differential pairs, see wikipedia, any analog ic book, or chapter 4 of designing analog chips. the latter is an excellent book written by hans camenzind, the inventor of the 555 timer, so definitely check out the pdf version. [10] widlar wrote a detailed explanation of the lm108 in ic op amp beats fets on input current (national semiconductor application note 29, dec 1969). [11] to protect the input transistors, transistors q3 and q4 boost the input transistor emitter voltage by two diode drops to make the voltages match. transistors q5 and q6 are in a cascode configuration. the result is the collector-base voltage of the input transistors is effectively zero, protecting them. [12] a current mirror is a very useful way of connecting transistors so the current through the second transistor matches the current through the first transistor. for more information about current mirrors, you can check wikipedia or any analog ic book such as chapter 3 of designing analog chips. [13] the lm108's four-transistor current source is configured so the four base-emitter junctions cancel out, except that one transistor has 10 times the base area of the remainder. the voltage generated across r20 is kt/q * ln(10), which is approximately 60mv at room temperature, but proportional to absolute temperature. (the principle of using emitters of different areas is similar to a bandgap voltage reference. however, the bandgap reference is configured so the temperature dependency cancels out and the voltage is stable.) the resistance of r20 controls the current into the current mirror. the temperature dependence is used to counteract temperature dependence of other parts of the circuit. a field-effect transistor (q30) generates the small current that powers the lm108's current source. the current source circuit turns the unpredictable current from q30 into a stable output current. for a full explanation, see patent 3930172. [14] the lm11 op amp is discussed in detail in reducing dc errors in op amps (national semiconductor technical paper 15) by widlar. [15] in some precision chips, the resistance can be tuned on a per-chip basis, for instance by laser-trimming the resistor or using zener zapping. this is not the case in the lm108; the resistances are controlled by the metal layer, which requires a new mask if it is changed. [16] two more strange transistors are shown below, with unconnected oval emitters. closeup of two strange transistors on the lm108 die. the schematic symbol (below) is even more puzzling, showing transistors with two emitters and two bases. while transistors with two emitters are common in integrated circuits, i've never seen two bases in one transistor. after discussion on /r/askelectronics, my theory is the second emitter is tied off on the lm108 but used on the lm11 for the balance inputs. symbol on the schematic for two strange transistors inside the lm108 op amp. no comments: links to this post email thisblogthis!share to twittershare to facebookshare to pinterest labels: electronics, reverse-engineering inside a rfid race timing chip: die photos of the monza r6 i recently watched a cross-country running race that used a digital timing system, so i investigated how the rfid timing chip works. each runner wears a race bib like the one below. the bib has two rfid tags, consisting of a metal foil antenna connected to a tiny rfid (radio-frequency identification) chip. at the finish line, runners pass over a pad that reads the chip and records the finish time. (i'm not sure why there are two rfid tags on each bib; perhaps for reliability of detection.) this race bib has two rfid chips and antennas for timing the race. the rfid chips are tiny black specks in the small loop of each antenna. the die photo below shows the rfid chip used on these tags. to create it, i took 22 photos of the chip with my metallurgical microscope and stitched them together to create a high resolution photo. (click the image for a larger version.) to prepare the chip, i removed it from the plastic carrier with goof off, dissolved the antenna with pool acid (hcl), and burnt off the mounting adhesive over a stove. this process left the chip visible with just a bit of debris that wouldn't come off. i'd probably get better results with boiling sulfuric acid, but that's too hazardous for me. i described the image stitching process in this article. die photo of the impinj monza r6 rfid chip. the chip turns out to be the monza r6 rfid chip built by impinj, a leading rfid chip company. the chip datasheet includes a die photo of the chip (below), but it is mostly obscured for some reason. even so, it is clear that the chip in the datasheet matches the one i photographed. die photo of the monza r6 rfid chip from the datasheet. most of the chip is obscured; the antenna contacts are visible at the top. how rfid timing works the basic idea of rfid timing is the finish line has an rfid reader connected to a directional antenna. when the runner crosses the finish line, the reader communicates with the rfid chip on the runner's tag, determines the runner's id number, and records the elapsed time. you might expect that the rfid chip simply returns the runner's number as the runner crosses the finish line, but there's a complex two-way protocol at work here. the chip uses the industry-standard epc standard, and supports about a dozen commands: select, query, read, write, lock, and various others. (while some rfid chips include cryptography, the r6 does not.) the chip receives commands from the reader and responds according to the protocol. the chip's memory includes an electronic product code (epc), which is a 96-bit universal identifier. in this case, the epc value is returned to identify the runner. one interesting thing is the rfid chip has no power source other than the radio signal; it is passive and doesn't need a battery. the reader transmits a radio signal (between 860 and 960 mhz), which is picked up by the antenna on the tag. the tiny amount of power received by the tag is what powers the rfid chip. to send data to the rfid chip, the reader pulses the radio signal it emits. the chip detects these pulses and converts them into bits, using various modulation schemes (details). you might expect the chip transmits a radio signal to send data back to the reader, but it doesn't have enough power to do that. instead, the chip dynamically changes load on the antenna (basically a transistor shorts out the antenna) while the reader is sending the radio signal. this causes a tiny change in the signal strength at the reader (about 1 part in 1000), which the reader can detect. this process, called backscatter, allows the chip to send data back to the reader without using power. you might wonder how the system works if two runners cross the finish line at the same time—how do both tags get read without interference? rfid tags are designed for inventory systems, so they are designed to handle environments where there are hundreds of tags in range of the reader. they use an efficient anti-collision protocol. the reader can minimize collisions by querying a subset of tags at a time ("i only want to hear from tags whose ids start with 123.") by rapidly iterating through subsets, a large number of tags can be queried with minimal conflicts. collisions are handled using a protocol called the q-algorithm. essentially, each tag waits a random amount before responding, so hopefully there won't be a collision. if there is a collision, tags wait a longer random amount next time until they can respond without collisions. this is based on the aloha protocol, which was also used to handle collisions on ethernet networks. inside the chip below is another die photo. i took this one earlier in the cleaning process, so there is more debris on the chip surface. the colors are slightly different in this photo due to different microscope camera settings. die photo of the monza r6 rfid chip. because the chip is complex and has multiple layers of metal, i was unable to analyze its circuitry in detail. however, i can make some informed speculation about it. the top part of the chip is the analog circuitry, extracting power from the antenna, reading the transmitted signal, and modulating the return signal. the two antenna contacts are the large gold pads at the top (on the left and right). the rectangles between the antenna contacts are probably transistors and capacitors forming a charge pump to extract power from the radio signal (see patent). the voltage received from the radio signal is about 200 millivolts, while the chip's circuitry requires about 1 volt. the charge pump boosts the incoming voltage to the higher voltage required. the middle of the chip has the logic circuitry. given the complex protocol that the chip handles, you might expect a microprocessor to control the chip. but it uses a complex state machine instead, presumably to keep the chip small and reduce power consumption. this is probably build from cmos standard digital logic cells, connected by the visible wiring (horizontal lines). this logic includes a pseudo-random number generator to support the anti-collision algorithm. the chip has the label "impinj kelso". it's unclear why it is labeled "kelso" and not "r6". i couldn't find any references to a "kelso" chip, so this could be an internal name. the impinj company is in seattle, washington and kelso is a small city in washington, so perhaps that's the connection. the bottom third of the chip likely contains the storage. the black rectangles above and below the impinj kelso text are probably the 12 bytes of non-volatile memory (nvm) that hold the tag identification. (this is essentially flash memory.) this impinj patent discusses the nvm system. writing the memory requires about 12 volts, which is provided by another charge pump. the gold squares scattered across the chip are probably test points used to program the chip and verify proper operation during manufacturing. these chips are really small let me emphasize how tiny the rfid chips are—they are specks, about the size of a grain of salt. according to the datasheet, the chip is 464.1µm x 400µm (about 1/64 inch on a side). this is much smaller than a typical ic, and explains why the rfid chip doesn't break if the tag is flexed. the biggest problem i had with the die photos was making sure i didn't lose the chip. if i brushed against the chip it could stick to my finger and vanish until i carefully searched my hands to find it. the image below shows the monza 4, a similar but slightly larger rfid chip, on top of a penny, next to a grain of salt. (a couple months ago, i wrote about the monza 4 chip and how it is times the bay to breakers race.) the rfid chip used to identify runners is very small, about the size of one of the letters on a penny. a grain of salt (next to r) and the rfid chip (on top of u). this chip has four antenna contacts. the antenna closeup of the rfid antenna and chip. the chip is the black speck in the center above dogbone, below the + sign. the two halves of the antenna are seemingly shorted together, but that's an important part of the rf impedance matching. the antenna seems straightforward at first—two metal strips connected to the chip. but if you look more closely, you'll notice that the strips are joined together above the chip, which would short out the signal. how does this work? the short answer is it's rf magic. the longer answer is the antenna is carefully designed to match impedance between the transmitter and the chip, so as much power as possible is received by the chip. the central part of the antenna is the "loop" and the two long parts of the antenna are the "dipole". the loop doesn't short out the dipole, but instead they work together. the area of the loop acts as an antenna, and the dipole provides the appropriate impedance so the system resonates at the right frequency. the "dogbone" antenna shape isn't artistic but helps fit a longer dipole into the available area. rfid antennas are explained in more detail in this application note. the tag (combining the antenna and chip) is produced by smartrac (whose name is barely visible under the black text), and sells for about 13 cents. the rfid system is similar in some ways to the nfc (near-field communication) that smart phones use for tap-and-pay. the following infographic summarizes the differences (full size). this infographic is courtesy of atlasrfidstore. conclusion the rfid chips used for race timing are very small but include a lot more complexity than you'd expect. i took some die photos of the monza r6 chip that show the analog and digital circuitry crammed into a piece of silicon the size of a grain of salt. the chip manages to power itself off the radio signal, allowing it to operate without a battery. this circuitry supports a complex communication protocol between the rfid tag and the reader. the foil antenna is carefully designed to maximize power transfer to the chip. all this is combined into a tag that sells for under 13 cents. i announce my latest blog posts on twitter, so follow me at kenshirriff. 5 comments: links to this post email thisblogthis!share to twittershare to facebookshare to pinterest labels: electronics, reverse-engineering simulating a xerox alto with the contralto simulator: games and smalltalk the revolutionary xerox alto computer came out in 1973 and set the direction for personal computing. if you want to try out the alto's software, the easiest approach is the contralto simulator. this article describes how to set up the contralto simulator, explains where to find alto disk images, and shows some of the programs you can run on it. if you're just joining this series, the alto was designed at xerox parc in 1973 to investigate personal computing. it introduced the gui, ethernet, high-quality computer typography and laser printers to the world, among other things. the alto was used to build smalltalk, which was one of the first object-oriented programming languages and had a huge influence on modern programming languages. y combinator received an alto from computer visionary alan kay, who led the smalltalk research at parc. i'm helping restore the system, along with marc verdiell, carl claunch luca severini, ed thelen, and ron crane. the contralto simulator (developed by josh dersch at the living computer museum in seattle) has been very helpful in our restoration—we can debug by comparing our real system to the simulator. if you're in the seattle area, you can see a couple running altos at this museum. using contralto contralto is written in c# and only works on windows. to install contralto, download the zip file. open the zip file and click on contraltosetup.msi to run the standard installer. next, you'll need a xerox alto disk image. the real alto uses 14" removable disk packs that hold 2.5 megabytes, as shown in the photo below. a disk pack is loaded into the alto, the system boots off the disk, and then disks can be swapped as necessary. the simulator replaces this process by loading a disk image file into the simulator. there are several archived disk images that you can use. one source is bitsavers.org. download an image file, such as allgames.dsk. inserting a disk into the xerox alto's disk drive. the alto's video display is visible at the back. next, run contralto and tell it to load the disk image: select "system -> drive 0 -> load". select allgames.dsk. then start the simulator with: "system -> start" (or reset if its already running). (also see the readme file.) after a few seconds, the contralto simulator should start up and show you the alto boot screen and command line prompt. at the > prompt, hit ? to see the list of files on the disk. files ending with .~ or .run are programs you can execute (by typing the file name). note that the simulator takes control of your mouse. to release the mouse cursor, press alt. click the mouse inside the window to give focus back to the alto simulation. the easiest way to stop a program is to hit alt and then select system -> reset. typing a question mark at the xerox alto executive prompt displays the contents of the disk. the "file / system / help" menu items are for the contralto simulator, not part of the alto gui. one of the games on the disk is space invaders, which can be run by simply typing "invaders". the game is controlled by using the three mouse buttons for left, shoot, and right. this game illustrates the bitmapped graphics of the alto, an unusual feature for that era due to the high price of memory. the xerox alto has a space invaders game, controlled by the mouse buttons. star trek was clearly popular with the alto programmers. the allgames disk lets you battle klingons with the spacewar game (below). it also includes trek, one of the first networked multiplayer games, which took advantage of the system's ethernet. the spacewar game on the (simulated) xerox alto lets you battle klingons. smalltalk smalltalk is a highly-influential programming language and environment that introduced the term "object-oriented programming" and was the ancestor of modern object-oriented languages. smalltalk was developed on the xerox alto by alan kay, dan ingalls, adele goldberg and others. the alto's smalltalk environment is also notable for its creation of the graphical user interface with the desktop metaphor, icons, scrollbars, overlapping windows, popup menus and so forth. when steve jobs famously visited xerox parc, the smalltalk gui inspired him on how the lisa and macintosh should work; the details of the visit are highly controversial but the description in dealers of lightning seems most accurate. to start up smalltalk, download st80.dsk. load the disk image into contralto, reset, and then run "resume small.boot". (a second smalltalk disk is xmsmall.zip; "resume xmsmall.boot" starts smalltalk from this disk.). i should mention that the smalltalk system is fairly slow, so be patient. smalltalk-80 running on the xerox alto simulator. the large window is the class browser. the smalltalk environment includes a class browser window (center) that lets you explore all the classes in smalltalk. reflection, being able to examine all the structures of a running system, was a key feature of smalltalk. programming in smalltalk is too complex to explain here, so i'll just give a simple example of executing an expression. in the upper-left window, type 355.0/113.0 followed by the cursor down key. (cursor down simulates the alto's line feed (lf) key, which ends a command. return will not work.) while this looks like a simple expression, it is object-oriented. the message "/113.0" is sent to the float object "355.0" (a subclass of number), executing the division method. (see this document for more information on alto smalltalk.) smalltalk also includes an image editor called bitrect. to start it, enter "bitrect new fromuser; edit" (and then cursor down) into the upper-left window, and select the size of the editor window with rubber-banding. the editor includes various tools, brush sizes and gray levels. note that the drawing window can overlap other windows. using the bitrect class in smalltalk to draw an image. the workspace window in the upper right has useful smalltalk commands to select and execute. writing bcpl code you can use the simulator to write code in the bcpl language. (bcpl was the precursor to c and is essentially c with a different syntax and no data types.) for the bcpl environment, download and uncompress the tdisk4.dsk.z">tdisk4.dsk.z image. code is edited using bravo, the first wysiwyg document editor. one consequence of using this editor is that code on the alto can have all the formatting and styling of a document: a variety of proportionally-spaced fonts, bolding, italics, and so forth. (being able to style code is a nice feature that can make code easier to understand, so the modern approach of writing programs with plain unformatted text seems like a step backwards.) the image below shows some bcpl code with formatting applied; the styling has no effect on the code's operation. i wrote an article earlier explaining how to use the bravo editor and the bcpl compiler, so see that article for details on writing bcpl programs. the bravo editor provides wysiwyg formatting of text. this bcpl program prints "hello world", using the ws (write string) function. the diagnostics disk if you want to follow along with our alto restoration, we're currently using a copy of the diagnostic disk diags.zip. (you'll need to unzip the disk image before loading it.) this disk includes the keyboard test, madtest microcode test, crt test and other diagnostics we have used in our blog posts and videos. the contralto debugger the contralto simulator includes an extensive debugger that lets you examine the running state of the (simulated) alto. this feature was very helpful for us when debugging the real alto, since we could compare what was supposed to happen with what was really happening. if you want to see what the alto does internally, or how microcode interprets machine instructions, give the debugger a try. you'll find that it takes many micro-instructions to execute one machine instruction, and many machine instructions to do anything useful. to start the debugger, select "system -> show debugger". this opens up a debugger window, as seen below. the left panel shows the source code for alto's microcode. the upper center panel shows disassembled machine instructions (using the nova instruction set). clicking "step" will single-step through the microcode. clicking "nova step" will step through nova code. click "run" to return to normal execution debug window for the contralto simulator. the left pane shows the microcode. the upper center pane shows the nova program instructions that are running. conclusion if you don't have a xerox alto available, the contralto simulator is the best way to get the alto experience. i should emphasize that i didn't write contralto; i'm just a user. josh dersch at the living computer museum wrote it. the museum also has a couple running altos, so stop by the museum if you're in seattle. for updates on the alto restoration, follow me on twitter at kenshirriff. 4 comments: links to this post email thisblogthis!share to twittershare to facebookshare to pinterest restoring yc's xerox alto day 10: new boards, running programs, mouse problems last week our vintage alto was crashing; we traced the problem to an incompatibility between two of the processor boards. today we replaced these boards and now we can run all the programs on the disk without crashes. unfortunately our mouse still doesn't work, which limits what we can do on this gui-based computer. we discovered that the mouse has the wrong connector; even though it plugs in fine, it doesn't make any electrical connection. if you're just joining, the alto was a revolutionary computer designed at xerox parc in 1973 to investigate personal computing. it introduced the gui, ethernet and laser printers to the world, among other things. y combinator received an alto from computer visionary alan kay and i'm helping restore the system, along with marc verdiell, carl claunch luca severini, ed thelen, and ron crane, incompatibility in the alto's circuit boards the xerox alto was designed before microprocessor chips, so its processor is built from three boards full of ttl chips: the alu (arithmetic-logic unit) board, the control board, and the cram (control ram) board. the control board and the cram board are the ones that we dealt with today. last week we traced through software execution, microcode, and hardware circuitry to figure out why some programs on the alto crashed. we discovered that the problem happened when a program attempted to execute microcode stored in the control ram. the microcode ram select circuit malfunctioned due to some wiring added to the back of the control board (the white wires in the photo below). why had this wiring been added to the board? and why did it break things? at the end of last episode, we briefly considered ripping out this wiring, but figured we should understand what was going on first. this is the xerox alto control board, one of three boards that make up the cpu. the board has been modified with several white wires which trigger our crashes. a bit of explanation will help understand what's going on. like most computers, the xerox alto's instruction set is implemented in microcode. the alto is more flexible than most computers, though, and allows user programs to actually change the instruction set by modifying the microcode, actually changing the instruction set. to achieve this, the alto stores microcode in a combination of ram and rom.[1] the default microcode (used for booting and for standard programs) is stored in 1k of rom on the control board. some programs use custom microcode, which allows them to modify the computer's instruction set for better performance. this microcode is stored in high-speed ram on the control ram (cram) board. our alto came with a 1k cram board, but some programs (such as smalltalk) required the larger 3k cram board.[2] (this microcode ram is entirely different from the 512 kbyte ram used by alto programs; you didn't need to fit an alto program into 3k.) inconveniently, the 1k and 3k ram boards have incompatible connections, and the control board needs to be wired to work with one or the other. we determined that the white-wire modifications on our control board converted it from working with a 1k ram board to working with a 3k ram board.[3] unfortunately, our alto had a 1k ram board so the two boards were incompatible and programs that attempted to use the microcode ram crashed, as we saw last week. it's a mystery why our alto had two incompatible board types, but at least we knew why the modifications are there. (since our alto also came with the wrong disk interface card and an unbootable hard disk, we wonder what happened to the alto since it was last used. it clearly wasn't left in a usable state.) fortunately al kossow of bitsavers came to our rescue and supplied us with some 3k control ram boards and the control boards to go with them. this saved us from needing to rewire the board we had. al also provided the strange but necessary connector (visible below on the left) that goes between the control board and the cram board. we swapped these boards with our boards and everything worked without crashing! we could now run all the programs on the disk without crashes. the alto's control board is part of the cpu. this board contains 2k words of microcode rom, as well as control circuitry. our original board had 1k of rom (and 8 empty sockets), while this board has the full 2k of rom. the rom chips are in the lower left, with labels. the chip labeled sw3k (upside down) is the prom that selects the hardware configuration. the spare prom (labeled sw1) is in the upper left. the edge connector on the right plugs into the backplane, while the two connectors on the left are cabled to the cram board. some alto software with the alto running reliably, we could try out the various programs on the hard disk that had crashed before. draw, the alto's mouse-based drawing program, apparently uses microcode for optimizing performance, so last week it immediately dropped into the swat debugger. with the compatible boards, draw ran successfully. unfortunately, since our mouse isn't working, we couldn't actually draw anything, but you can still see the icon-based gui below. i've tried draw on the alto simulator, and despite the icons, it's not exactly intuitive to use. 'draw' is the alto's mouse-based drawing program. clicking an icon on the left selects an operation. we also tried bravo, the first wysiwyg (what you see is what you get) text editor. again, functionality is limited without the mouse. but i could enter text and change the font to a larger, bold font with proportional spacing. xerox parc also invented the laser printer and ethernet, so one could create documents in bravo and then print them on a networked laser printer. charles simonyi, one of the co-authors of bravo, later created microsoft word, so there's a direct connection between the alto's editor and word. i've written more about how to use bravo here. 'bravo' is the alto's wysiwyg text editor. it supports multiple fonts, among other features. the alto included a gui file manager called neptune, allowing files and directories to be manipulated with the mouse. neptune has an invisible scroll bar to the left of the file list that appears when you mouse-over it; apparently the alto also invented the scroll bar. the alto includes a graphical file system browser. a rather complex gui is in prepress, a program that converted a spline-based font to a bitmapped font for display or printing. (you can think of this as a forerunner of truetype fonts.) high-quality fonts were created for the alto using the fred font editor. as you would expect from a document company, these fonts included proportional spacing, ligatures such as "ffl" and "fl", and multiple styles and sizes. 'prepress' is used to convert a spline-based font into a bitmap suitable for display or printing. most importantly, we were able to run madtest, the microcoded alto diagnostic test, which runs a suite of low-level diagnostics using microcode. this test ran successfully, increasing our confidence that there are no obscure problems in the processor. if you want to try these alto programs for yourself, you can use the contralto simulator, built by the living computer museum. this simulator has been very useful to use for learning how the software is supposed to work. the mouse the biggest problem remaining at this point is the mouse doesn't work, so we investigated that next. although the mouse was invented prior to the alto, the alto was the first computer to include the mouse as a standard input device. the alto uses a three-button mouse that plugs into the back of the keyboard. the three-button optical mouse. some altos had a mechanical mouse, while others had an optical mouse. our alto came with an optical mouse, but we couldn't get it to work at all. the mouse uses a special mousepad with a specific dotted pattern (which we didn't have), so at first we suspected that was the problem. however, the mouse didn't respond at all when we used a printed copy of the pattern. we also didn't see any light (visible or ir) from the three illumination leds on the mouse, so we suspected bigger problems than a missing mousepad. underside of the mouse. the sensor (right) consists of three illumination leds surrounding the optical sensor. opening up the mouse shows the simple circuitry inside, with a single chip controlling it. the chip is rather unusual since it includes a 16-pixel optical sensor, with a light guide that goes from the bottom of the chip to the bottom of the mouse. the pixel-based optical mouse was invented at xerox parc in 1980 (and later patented), so this mouse is somewhat more modern than the original alto (1973). the handwritten markings on the chip suggest this may have been a prototype of some sort. inside the optical mouse. in the middle are the three buttons. at top is the ic that contains the optical sensor. when we closely looked at how the mouse was wired up, we discovered the problem. the mouse plugs into a 19-pin socket (de-19), while the mouse used a 9-pin plug (usually called db-9, but technically de-9), so the connectors are entirely incompatible. the de-19 has three rows of pins: 6/7/6 (with the middle row empty on the alto), and the db-9 has two rows of pins (7/6). the bizarre thing is that the mouse plugged into the socket just fine: the connector shells are physically the same size, and the mouse plug's pins went between the alto socket's connections. so the mouse was plugged in, but not actually connected to anything! it's surprising the connectors could go together without bending any pins. (several people have suggested sources for a db-19 connector. unfortunately the de-19 (three rows) has a totally different shape from the db-19 (two rows).) the alto's mouse plugs into the 19-pin connector on the keyboard housing (above). unfortunately our mouse has a 9-pin connector (below). after some investigation, we learned that the alto was missing the mouse when it came from alan kay. ycombinator picked up a replacement mouse on ebay, but it wasn't compatible with our alto. we're still trying to figure out if the mouse is an alto mouse with a nonstandard connector or if it is for a different machine. the xerox star used a 2-button mouse, so the mouse isn't from a star. tim curley at xerox parc loaned us a compatible alto mouse, so we'll give that one a try next episode. we're also looking into making an adapter cable, but de-19 connectors appear to be obsolete and difficult to find. conclusion last week we discovered that the control board in our alto was incompatible with the microcode ram board. al kossow loaned us some compatible boards, and with those boards our alto has been functioning without any crashes or malfunctions. we discovered that our mouse wasn't working because it had the wrong connector—although it plugged into the alto, it didn't make any electrical connection. since the mouse is necessary for many alto programs, we hope to get the mouse working soon. for updates on the restoration, follow me on twitter at kenshirriff. thanks to al kossow for helping us out again. notes and references [1] the table below shows the three microcode configurations the alto supported. details are in section 8.4 of the hardware manual. the desired configuration is selected by inserting a particular prom in the control board: sw1, sw2, or sw3k. each control board has one prom in use and an unused prom in the upper left corner; switching proms switches the configuration. the control board has sockets for 2k of rom; these sockets are left empty for systems with 1k of rom. configuration nameromram 1k 1k 1k 2k 2k 1k 3k 1k 3k [2] the alto introduced the 3k ram board to take advantage of the new 4 kilobit ram chips, replacing the 1 kilobit chips on the 1k board. both boards required 32 ram chips for the 32-bit micro-instructions, showing that back then you needed a lot of chips for not much memory. the microcode required high-speed static memory, so density was worse with microcode than with regular ram. [3] the 3k ram board requires a few additional signals from the control board, such as the task id. the 1k ram board grounds one of the lines used for these signals, so using the 3k control board with the 1k ram board (as our alto did) shorts out one of the bank select lines. this causes bank switching to fail and explains the crashes we saw last week. schematics for the boards are available at bitsavers. 13 comments: links to this post email thisblogthis!share to twittershare to facebookshare to pinterest labels: alto, electronics restoring yc's xerox alto day 9: tracing a crash through software and hardware last week, after months of restoration, we finally got the vintage xerox alto computer to boot (details) and run programs. however, some programs (such as the mouse-based draw program) crashed so we knew there must still be a hardware problem somewhere in the system. in today's session we traced through the software, microcode and hardware to track down the cause of these crashes. for background, the alto was a revolutionary computer designed at xerox parc in 1973 to investigate personal computing. it introduced the gui, ethernet and laser printers to the world, among other things. y combinator received an alto from computer visionary alan kay and i'm helping restore the system, along with marc verdiell, luca severini, ron crane, carl claunch and ed thelen. the full collection of alto restoration posts is here. when the xerox alto encounters a problem, it drops into the swat debugger. to assist with debugging, the alto includes a debugger called swat. if a program malfunctions, it drops into the swat debugger, as seen above. the debugger lets you examine memory and set breakpoints. it is more advanced than i'd expect for 1973, including a feature to disassemble machine instructions from memory and view them with names from the symbol table. in our case, the debugger showed that when we ran the madtest test program, the alto had jumped to address 2, which triggered the debugger. the first 8 memory locations in the xerox alto contain trap instructions to catch erroneous jumps to a zero address (or near-zero address) which can happen if a subroutine return address is clobbered. by examining the stack frames, i determined which subroutine had been called when the system crashed. the problem occurred when the program was jumping to microcode that had been loaded into microcode ram, since this is an unusual operation, it would explain why most programs ran successfully and only a few crashed. microcode microcode is a low-level feature of most processors, but i should explain what it means for a program to jump to microcode, since this is a strange feature of the alto. computers execute machine code, the simple, low-level instructions that the cpu can understand; on modern computers this may be the x86 instruction set, while the alto used the data general nova instruction set. most processors, however, don't run machine instructions directly, but have a microcode layer that is invisible to the programmer. while the processor appears to be running machine instructions, it internally executes microcode, a simpler, low-level instruction set that is a better match for the hardware. each machine instruction may turn into many micro-instructions. the xerox alto uses microcode much more extensively than most computers, with microcode performing tasks such as device control that most computers do in hardware, resulting in a cheaper and more flexible system. (as alan kay wrote, "hardware is just software crystallized early.") on the alto, programmers have access to the microcode—a user program can load new microcode into special control ram. this microcode can implement new machine instructions, optimize particular operations (analogous to gpu programming), or obtain low-level control over the system. the xerox alto's cram board (control ram) stores 1024 microcode instructions. the 32 memory chips in the lower left provide the 1024x32 storage. foreshadowing: the connector at the lower left connects the cram board to the microcode control board. our alto has 1024 words of microcode in rom (for the standard microcode) and 1024 words in ram (for software-controlled microcode). the photo above shows the cram (control ram) board that holds the user-modifiable microcode. this board illustrates the incredible improvements in memory density since 1973—this board required 32 memory chips to hold the 1024 32-bit words (4 kbytes) of microcode. the alto's microcode uses a 1k (10-bit) address space. since altos can support up to 2k of microcode in rom and 3k in ram, bank switching is used to switch between different 1k memory banks. bank switching is triggered by a special micro-instruction called swmode (switch mode). getting back to our crash, the madtest test program loads special test microcode into the control ram. then it executes the jmpram machine instruction to switch execution from machine instructions to the microcode in ram. the microcode that implements jmpram performs a swmode to switch execution to the ram microcode bank and the microcode in ram will execute. when the microcode is done, it is supposed to return execution to the machine code emulator, and execution of the user-level program (madtest) will continue. but somehow execution ended up at address 2, causing the program to crash. to track down a problem with the xerox alto's bank switching circuit, we attached many probes to the cpu control board. we used a logic analyzer to record every micro-instruction and memory access, so we could determine exactly what went wrong. after a few tries, we captured a trace showing what the alto was executing until it crashed. over the past week, i've been using the living computer museum's contralto simulator of the xerox alto to understand how the alto's software and microcode work. with this background, i could interpret the logic analyzer output and map it to the madtest code and the microcode. everything proceeded fine until the jmpram instruction was executed. instead of switching to the microcode in ram, it was still running microcode from the rom. since the micro-address was intended for the ram code, the processor was running essentially random microcode. through pure luck, this microcode routine completed and returned control to the regular machine code emulator rather than hanging the system. unfortunately this code didn't load the return address register, resulting in a jump to address 2 and the swat crash we saw. to summarize, everything was working fine except instead of switching to the microcode ram bank, execution stayed in the microcode rom bank. this was pretty clearly a hardware problem, so we started looking at the bank switch circuit, which consists of multiple integrated circuits. the bank switch hardware the alto was built at the dawn of the microprocessor age, so instead of using a microprocessor chip, it used three boards of ttl chips for the cpu. the control board interprets the microcode, including performing bank switching, so that's where we started our investigation. bank switching in the alto happens when the swmode micro-instruction is executed. the destination bank is selected following complex rules that depend on the hardware configuration and the current bank. rather than implement these rules with a complex hardware circuit, the alto designers used the short cut of encoding all the logic into a 256x4 prom chip. (this also has the advantage that a different hardware configuration can be supported simply by replacing the prom.) the schematic below shows the prom (left) generating the bank select signals (yellow), which pass through various chips to create the current bank select signals (right), which are fed back into the prom for the next cycle. this schematic shows the xerox alto's bank switching circuit, allowing microcode to run from rom or ram banks. (click for larger image.) we connected logic analyzer probes so we could trace each chip in the bank select circuit. the prom correctly generated the ram bank signals when the swmode micro-instruction executed, but in the next step its inputs had reverted to the rom bank for some reason. this showed the prom worked, so we continued probing through the circuit. each chip had the proper output until we got to the multiplexer chip that feeds back to the prom. (this chip, on the right, handles microcode task switching by selecting either the current task's bank, or the new tasks's bank, which is recorded in a ram chip.) the input signal to the multiplexer pulsed high for the new bank, but the output stayed low, blocking the bank switch signal. the oscilloscope trace below shows the problem: the input signal (bottom trace) is not passed to the output (middle trace). a multiplexer ic in the xerox alto was failing to pass the bank switch signal from its input (bottom trace) to its output (middle trace). we found a bad chip on the disk interface board a few weeks ago, so had we located a second bad chip? we pulled out the suspicious chip (a 74s157 multiplexer) and tested it in a breadboard to prove that it was faulty. surprisingly, it worked just fine. perhaps the problem only showed up at high frequency? we swapped it with an identical chip on the board and the crash still happened. clearly there was nothing wrong with the chip. but its output stayed low when it should go high. why was this? we thought this 74s157 multiplexer ic from the xerox alto was faulty. however, the chip worked fine when tested in a breadboard. our next theory was that something was grounding the chip's output signal, forcing the output to remain low. to test this, we disconnected the chip's output pin from the rest of the circuit by bending the pin so it didn't go into the socket, with the output not connected to the circuit, the output went high as expected. (see oscilloscope trace below.) this proved that the chip worked and something else was pulling the signal low. since the chip's output was connected to the prom chip, the obvious suspect was the prom, which might have an input shorted low. we hoped the prom chip wasn't at fault, since locating a 1970s-era d3601 prom chip and reprogramming it would be inconvenient. we pulled the prom chip out of the board and the short to ground remained, demonstrating the prom chip was not the culprit. with the multiplexer's output disconnected from the circuit, the input signal (bottom) appears on the output (top) as expected. we removed the control board from the alto to examine it for short circuits. on the back of the circuit board, we noticed that two white wires were connected to the multiplexer chip that was causing us problems. (wires are added to printed circuit boards to fix manufacturing problems, support new features, or support new hardware.) these wires went to the connector that was cabled to the cram (control ram) board shown earlier. with the cram board disconnected, the short to ground went away. thus, the cause of our crashes was these two wires that someone had added to the board! could we simply cut these wires and have the system work correctly? we figured we should understand why the wires were there, rather than randomly ripping them out. maybe our control board and cram board were incompatible? maybe these wires were to support the trident disk drive we aren't using? it was the end of the day by this point, so further investigation will wait until next time. this is the xerox alto control board, one of three boards that make up the cpu. the board has been modified with several white wires which trigger our crashes. conclusion after a bunch of software, microcode and hardware debugging we found that the crashes are due to some wires added to one of the circuit boards. these wires messed up microcode bank switching, causing programs that used custom microcode to crash. fixing this should be straightforward, but we want to understand the motivation behind these wires. on the whole, the processor is working reliably other than this one issue. once it is fixed, we can run madtest (the microcode test program) to stress-test the processor. if there are no more processor issues, we'll move on to getting the mouse working. for updates on the restoration, follow me on twitter at kenshirriff. thanks to the living computer museum for the extender board and the contralto simulator. 3 comments: links to this post email thisblogthis!share to twittershare to facebookshare to pinterest labels: alto, electronics, oscilloscope older posts home popular posts intel x86 documentation has more pages than the 6502 has transistors a multi-protocol infrared remote library for the arduino a dozen usb chargers in the lab: apple is very good, but not quite the best a new multi-branch algorithm to render rational-exponent mandelbrot fractals: part i apple iphone charger teardown: quality in a tiny expensive package the z-80 has a 4-bit alu. here's how it works. fixing the core memory in a vintage ibm 1401 mainframe macbook charger teardown: the surprising complexity inside apple's power adapter labels 6502 8085 alto apple arc arduino arm beaglebone bitcoin c# calculator css electronics f# fractals genome haskell html5 ibm1401 ipv6 ir java javascript math oscilloscope photo power supply random reverse-engineering sheevaplug snark spanish teardown theory unicode z-80 power supply posts iphone charger teardown a dozen usb chargers magsafe hacking inside a fake iphone charger power supply history blog archive ▼  2016 (33) ▼  december (1) superbeta transistors inside: die photos and analy... ►  october (5) ►  september (8) ►  august (2) ►  july (3) ►  june (4) ►  may (1) ►  april (1) ►  march (1) ►  february (4) ►  january (3) ►  2015 (12) ►  december (2) ►  november (1) ►  october (3) ►  august (1) ►  may (2) ►  march (2) ►  february (1) ►  2014 (13) ►  december (1) ►  october (1) ►  september (3) ►  may (2) ►  march (1) ►  february (5) ►  2013 (24) ►  november (2) ►  september (4) ►  august (4) ►  july (4) ►  june (2) ►  april (1) ►  march (2) ►  february (2) ►  january (3) ►  2012 (10) ►  december (1) ►  november (5) ►  october (1) ►  may (1) ►  march (1) ►  february (1) ►  2011 (11) ►  december (2) ►  july (2) ►  may (2) ►  april (1) ►  march (1) ►  february (3) ►  2010 (22) ►  december (2) ►  november (4) ►  october (3) ►  august (1) ►  june (1) ►  may (2) ►  april (3) ►  march (4) ►  january (2) ►  2009 (22) ►  december (2) ►  november (5) ►  september (1) ►  august (3) ►  july (1) ►  june (3) ►  april (1) ►  march (3) ►  february (2) ►  january (1) ►  2008 (27) ►  july (3) ►  june (1) ►  may (3) ►  april (4) ►  march (10) ►  february (6) amazon.com widgets--> quick links arduino ir library 6502 reverse-engineering simple template. powered by blogger.


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