5 ms·
Inside the 76477 Space Invaders sound effect chip
- phab 8y agoThis is a fascinating article. Footnote 8 is an especially fascinating insight; > One puzzling feature of the shift register is that there is no wiring between the stages! > How do bits get from one stage to the next? Did the chip have another layer of wiring that wasn't in > the photos? Was there some sort of hidden connection? Eventually I noticed that there wasn't an isolation > ring between the stages—a silicon barrier that separated most I2L circuits. Without this isolation ring, > an "invisible" PNP transistor exists between the stages, apparently allowing one stage to flip the next > stage to the right value. Each shift-register stage is constructed from two NAND-gate latches. When the > clock is low, the first latch is forced into an indeterminate state. When the clock goes high, the latch > ends up as 0 or 1 based on the bias it receives from the previous stage through the "invisible" PNP > transistors. Thus, the latch becomes edge-sensitive since it will change right on the clock's rising edge. > I found a paper ("Injection-Coupled Synchronous Logic", 1978) that describes a similar technique for an I2L > shift register9, so I think this is the right explanation, even though the circuit seems a bit sketchy.
- sjwright 8y agoA direct link to the footnote, as the above is unreadable. (Hint: don’t use code formatting for quotes. It is semantically wrong and is unreadable on many devices.) http://www.righto.com/2018/05/inside-76477-space-invaders-sound.html?m=1#fn:connection http://www.righto.com/2018/05/inside-76477-space-invaders-so...
- digi_owl 8y agoThe basic problem is that it is "labeled" as a form of quote...
- phab 8y agoI'm curious as to why you find this unreadable... it renders pretty readably for me? (https://pasteboard.co/HlW8oMh.png https://pasteboard.co/HlW8oMh.png). As far as I can tell, formatdoc[0] doesn't provide a "semantically correct" method for formatting quotes. Hence, the age-old usenet quote (as codified in RFC3676[1]) seems to me to be the best way of indicating a quotation, and rendering it via a verbatim block ensures that the line-based quotation indication isn't disrupted by the text all being in a <p> tag when rendered in HTML. [0] https://news.ycombinator.com/formatdoc https://news.ycombinator.com/formatdoc [1] http://www.ietf.org/rfc/rfc3676.txt http://www.ietf.org/rfc/rfc3676.txt
- CamperBob2 8y agoSemantically wrong or not, it's all the HN developers have chosen to give us for blockquoting. That's not the users' fault. For mobile, it helps if you manually truncate lines, like so: One puzzling feature of the shift register is that there is no wiring between the stages! How do bits get from one stage to the next? Did the chip have another layer of wiring that wasn't in the photos? Was there some sort of hidden connection? Eventually I noticed that there wasn't an isolation ring between the stages—a silicon barrier that separated most I2L circuits. Without this isolation ring, an "invisible" PNP transistor exists between The site is called "Hacker News," after all. Apparently that's because we're expected to, well, hack.
- scarface74 8y agoItalics are more readable.
- CamperBob2 8y agoAnd semantically just as broken. Would it be that hard for the '1337 h4x04s at YC to support '>' blockquote markup like so many other forums?
- scarface74 8y agoSo what's more important "semantic correctness" or having a readable post?
- CamperBob2 8y agoThat question excludes an obvious middle ground, which is supporting a reasonable feature set in the BBS software so that the question never even comes up. Let's stop carrying water for lazy programmers. The lack of a proper quoting syntax has been a problem on HN for a long time.
- scarface74 8y ago
- pasbesoin 8y agoOn HN, you can just "star" the paste at the beginning and end. One puzzling feature of the shift register is that there is no wiring between the stages! How do bits get from one stage to the next? Did the chip have another layer of wiring that wasn't in the photos? Was there some sort of hidden connection? Eventually I noticed that there wasn't an isolation ring between the stages—a silicon barrier that separated most I2L circuits. Without this isolation ring, an "invisible" PNP transistor exists between the stages, apparently allowing one stage to flip the next stage to the right value. Each shift-register stage is constructed from two NAND-gate latches. When the clock is low, the first latch is forced into an indeterminate state. When the clock goes high, the latch ends up as 0 or 1 based on the bias it receives from the previous stage through the "invisible" PNP transistors. Thus, the latch becomes edge-sensitive since it will change right on the clock's rising edge. I found a paper ("Injection-Coupled Synchronous Logic", 1978) that describes a similar technique for an I2L shift register9, so I think this is the right explanation, even though the circuit seems a bit sketchy.
- deleted 8y ago[deleted]
- 2sk21 8y agoBrought back great memories. In the early 80s, I used this chip to build a small analog synthesizer. My dream was to build an Elektor Formant but had to settle for the 76477. But I learned a lot from that exercise
- _delirium 8y agoFor background, link to a discussion about the previous article [1] in the series: https://news.ycombinator.com/item?id=14232499 https://news.ycombinator.com/item?id=14232499 [1] http://www.righto.com/2017/04/reverse-engineering-76477-space.html http://www.righto.com/2017/04/reverse-engineering-76477-spac...
- kens 8y agoLast year's article described the analog parts of the sound chip The new article discusses the digital circuits and how they are implemented using I2L logic, a competitor to TTL.
- jacquesm 8y agohttps://news.ycombinator.com/item?id=14232499 https://news.ycombinator.com/item?id=14232499 Covered this material to some extent, there are quite a few comments. This is a different article though by the same author.
- deleted 8y ago[deleted]
- vatys 8y agoThis reminded me I have two of this chip sitting in my parts bin, with nice little DIP format adapter boards even. It bugs me that I bought the chips ~18 years ago and still haven't done anything with them. My project queue needs some reshuffling. I should start making synth modules again. Or I should find myself a Blacet Dark Star Chaos module. I should have bought one when I had the chance.
- scoot 8y agoHere's a home made synth: https://www.youtube.com/watch?v=nCsiJ8o3BEo https://www.youtube.com/watch?v=nCsiJ8o3BEo
- watmough 8y agoLol, I have a couple lying around I had earmarked for building a midi interface for. Maybe my 8-y/o daughter will 'grow into them' as she is the only person in the house with any ability to play keyboards.
- martyvis 8y agoI definitely bought this chip and a bunch of pots and caps and twiddled with it. While I had a full sized Yamaha organ at home to make music with, being able to invent my own sounds was almost more satisfying. I'm definitely more an engineer than an artist, but continually struggle to keep focused on bringing projects to conclusion as they interfere with each other.
- drudru11 8y agoOh man - loved that sound! This will be a great read this weekend.
- teilo 8y agoWow. I didn't realize that an analog synthesizer-in-a-chip was a thing that far back. Pretty remarkable. All the basics are there: oscillator, noise generator, filter, envelopes, lfo. Although it's not quite everything. The VCF is for noise only, and there's no way to insert a filter into the VCO audio path externally. However, that pretty much defines the "chip tune" genre.