--- Philip Pemberton <philpem_at_dsl.pipex.com> wrote:
> Do any of your docs say what "COSMAC" actually means? I was thinking
> along the lines of "Chip On Sapphire MAChine" or something like that...
Never thought of the origins, but that's an astute guess. I just
figured it was a catchy name invented by marketing.
> IIRC NASA used 1802s on some deep-space probes).
Voyager I and II, and Galileo (a recycled Voyager spare).
In addition to radiation resistance, the 1802 works down to 0 Hz - it
can be statically clocked - a buddy of mine built an Elf in high-school
and didn't own an oscilloscope - for debugging it, he used a debounced
switch and an analog VOM. He followed along the timing diagram in the
RCA docs and manually toggled it through the states (8 clocks per cycle,
2 or 3 cycles per instruction).
Unlike lots of modern processors, you can have an arbitrary amount
of time between clock ticks, providing for serious power savings
when a spacecraft is in cruise-along-and-ignore-things-for-weeks
mode. Just set an "alarm" to speed up the clock when an event comes
in, or every so often, then conserve for the rest of the trip (the
Voyager frame uses plutonium RTGs (radio-isotope thermal generators?)
for power, so it's not like you save on the batteries, but the principle
is the same - don't stress the equipment if you have nothing to do.
The 1802 is one of my 3 favorite microprocessors. As everyone else has
said, nice find.
-ethan
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Received on Mon Jun 17 2002 - 11:59:54 BST