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