[HN Gopher] The Apple-1's unusual MOS clock driver chip
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The Apple-1's unusual MOS clock driver chip
Author : picture
Score : 71 points
Date : 2022-03-21 17:46 UTC (5 hours ago)
(HTM) web link (www.righto.com)
(TXT) w3m dump (www.righto.com)
| russellbeattie wrote:
| Wow. I hadn't realized before today that the Apple I was
| basically a computer with a built-in character-only ASR-33
| teletype terminal for interacting with it. Or, said another way,
| it was a teletype terminal which happened to have its own
| computer inside to talk to.
|
| So, how did the Apple II end up using standard graphics memory
| which enabled games and such? From a 1984 Byte interview:
|
| > _Steve got intrigued with all these ideas and one day he asked
| me, "Why don't you use these new 16-pin dynamic RAMs?" I had
| looked at them in my work at Hewlett-Packard, but they were new
| and I couldn't afford any parts that didn't come my way almost
| free. I'm a little bit shy, and I didn't know any of the reps,
| but Steve just called them up and talked them into giving us
| samples. I jumped on it. I thought it was a great part because
| you could replace 32 chips on a board with just eight. It was a
| little more difficult to use because you had to multiplex the row
| and column addresses and that cost me one or two chips. But I was
| very happy because it was TTL [transistor-transistor 1ogic]
| compatible and I could save a lot of board space because the
| parts were so much smaller._
|
| I guess this also answers the question of what Jobs was doing
| while Woz was being a genius. These guys were 26 and 22 - the
| hacker and the hustler. Sooooo amazing.
| bitwize wrote:
| Without deep dives like this, it's easy to underestimate how much
| of a wizard Wozniak is.
| joezydeco wrote:
| The pinnacle of Wozniak hacks was the floppy disk controller,
| but this comes pretty close.
| jhallenworld wrote:
| I worked at a company that made video titlers in the 80s. They
| tried all kinds of interesting memory technology including bubble
| memory and CCD memory. I remember they deployed CCD shift
| register memory to customers, but it was pretty error prone- your
| text would get corrupted over time.
|
| They made a 68000-based high resolution titler with fast SRAM for
| the display refresh memory. This would have been crazy expensive
| except that the image was stored in compressed format, and
| decompressed on the fly during display, so they only needed
| something like 64KB. It looked great, but composing the image
| (from annotated text) was very slow. I think Chyron just used
| lots of DRAM in their similar products (pretty sure they used
| 8086).
| hughrr wrote:
| Philips used CCD shift registers in their very early digital
| oscilloscopes (PM3310/PM3311) as well. This was then shifted
| into an 8085 based computer which rendered it out to the
| display. Absolutely horrible scopes to use and repair however.
| Was the only way to get 50MS/s though in the 80s!
| LocalH wrote:
| I'm not sure what the earlier Chiron units used for a CPU (I
| think I read somewhere that the Chiron II used the DataMate-70
| minicomputer), but I'm pretty sure that Chyron's iNFiNiT!
| series used 68k CPUs (possibly a 68060 in the higher end
| units?).
|
| I think I've said this on HN before, but professional character
| generators are _woefully_ underdocumented. In a lot of ways,
| they were at the pinnacle of computing power (generating
| quality NTSC imagery is much more easier said than done). I 'd
| love to see something like an emulated Datavision D-3000 one
| day. Modern computers can push around video well enough that
| such things could actually be shoehorned into a modern workflow
| (make the emulator into an NLE plugin that is scriptable and
| you'd be much of the way there).
| randall wrote:
| Can we be friends? hn@randallb.com
| kens wrote:
| Author here if anyone has questions...
| kragen wrote:
| Did it use the Intel 1405 shift register chip, like the
| Datapoint 2200, or a different chip? I can't read the part
| numbers in the briefcase photo, and if the text names the shift
| register used, I missed it.
|
| With regard to serial memories, you mentioned the EDSAC and the
| IBM 2260, but maybe it's worth expanding on how common serial
| memories were; I don't know if you think it's worth mentioning
| in this context, but delay-line analog memory was in use in PAL
| TVs and VCRs up to at least the 01980s and I think the 01990s,
| often made from piezoelectrics and fused quartz, and 01960s
| digital calculators like the Olivetti Programma 101 used
| magnetostrictive wire-torsion digital delay lines for their
| memory https://www.nzeldes.com/HOC/DelayLine.htm, which is
| possibly something I originally learned from your own blog.
| Turing's Pilot ACE and the UNIVAC I used mercury delay lines
| http://ed-thelen.org/comp-hist/vs-univac-mercury-memory.html,
| and the LGP-30 used a magnetic drum as a sort of
| magnetoelectromechanical delay line for its 31-bit
| "architectural" registers. Also, coaxial and lumped-element
| analog delay lines (similar to Pupinized telephone lines)
| enabled analog oscilloscopes to plot signals from _before_ the
| trigger fired rather than only afterwards.
|
| More generally we could get into bubble memory, CCDs, SPI
| interfaces to RAM, hard disk tracks, etc., as some of the other
| commenters have mentioned.
| kens wrote:
| Thanks for the details on serial memories :-)
|
| The Apple-1 display used the Signetics 2504 shift register:
| https://www.applefritter.com/files/signetics2504.pdf
|
| It also used a Signetics 2519 6x40 shift register to hold one
| line: https://www.applefritter.com/files/signetics2519.pdf
| kragen wrote:
| Thanks! Maybe their PMOS nature (P-ness?) is the reason for
| the annoying voltages? I mean a (contemporary) four-phase-
| logic shift register wouldn't need those voltages, and of
| course neither do CMOS shift registers. Though I guess a
| 1024-bit CMOS shift register would still need a pretty good
| clock drive current, especially if fabbed at those sizes.
| hughrr wrote:
| No question, just a thank you and appreciation for your
| excellent articles.
| tenebrisalietum wrote:
| I think I saw it on an 8-bit Guy YouTube video - there's a
| screen clearing circuit. How did that work? If you can't access
| the shift registers in any method but sequentially how could
| the circuit clear the screen instantly?
| jandrese wrote:
| According to the article the chip was clocked at 1 Mhz and
| only had 1 kilobit of storage, so you should be able to zero
| it out in a millisecond, less time than it takes to blit a
| single frame.
| tlb wrote:
| How did the firmware modify the data in the shift register to
| write text? Did it require cycle-accurate delay loops to hit it
| at just the right cycle?
| kens wrote:
| It's pretty clever. One shift register held a bit to indicate
| the current cursor position. To write a character, the
| circuit waited until the cursor bit appeared and then updated
| the character shift registers. At the same time, the cursor
| bit was delayed to advance it to the next character. Note
| that you could only write characters sequentially; you
| couldn't write to arbitrary locations on the screen.
| JKCalhoun wrote:
| I thought Woz basically used Don Lancaster's TV Typewriter
| circuitry (also shift-register based memory).
|
| https://en.wikipedia.org/wiki/TV_Typewriter
| kens wrote:
| The Apple-1 display uses some ideas from the TV Typewriter
| (shift-register storage, another shift-register for a line,
| 2513 character ROM). But it is different in many ways, much
| simpler (the TV typewriter is 4 boards), and improved (24x40
| display instead of 16x32 for instance).
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