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On 2012-06-30, Peter Humphrey <peter@××××××××××××××.org> wrote: |
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> On Friday 29 June 2012 21:46:20 Grant Edwards wrote: |
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> |
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>> Things have been going steadily downhill since the days of V7 on a |
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>> PDP-11 with 256K words of RAM, a 20MB hard drive and uucp via dial-up |
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>> modems for "networking". Real programmers didn't _need_ more that |
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>> 64k of text and 64k data to get the job done. |
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> |
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> Sorry, but that's just bloat. When I joined the software development |
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> effort on the national grid control system in 1980 (I was the third of |
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> three) we had two Ferranti Argus 500 computers, one on-line and one |
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> standby, each with 32KB RAM (twice as much as the same machines had at |
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> the newly commissioning AGR power stations) |
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Touche! |
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> The displays were graphic stroke writers, as used in submarines and |
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> other warships - none of that nasty raster technology. I think the |
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> display drivers were more complex than the CPUs - all that D-A |
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> conversion of multiple values at once. Can you imagine X and Y |
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> amplifiers to drive a spot in a circle - and meet up? |
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That's actually pretty trivial: Feed a sine wave into X and cosine |
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into Y. AC amplitude controls size, DC offsets control position. |
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Hint: cosine is just sine phase shifted by 90 degrees, so you can do |
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that with a single resistor and capacitor. |
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> Then a display full of them. |
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Been there, done that. :) |
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It was one of the standard junior-level homework lab assignements when |
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I was in College back around 1980: design, build, and demonstrate a |
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circuit that would display the contents of a 2716 EPROM (in binary) on |
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an X-Y vector display (e.g. oscilloscope). It's not as hard as you |
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might think. All it takes is a a counter, a half-dozen gates, and |
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about three op-amps. It fit on one of these proto-boards: |
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http://www.busboard.us/photos/BPS-IMG-BB830.jpg |
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IIRC, it displayed one byte per line (eight '1' or '0' characters), |
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eight bytes per "page". It used a dip-switch to select what "page" |
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from the EPROM to display. Expanding the 8x8 display to something |
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like 128x64 would just require slightly longer counters. |
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-- |
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Grant |
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