M
Michael Black
But surely others have followed. I can't believe with all the
growth in CPUs, and space, that there aren't any other CPUs with
such rating.
I remember the late seventies and someone with AMSAT, the Amateur Radio
Satellite Corporation, came to talk at the local ham club meeting. He
made the point that the 1802 would be used in the upcoming amateur
satellite (or maybe it had been launched by then) because of the radiaion
hardening, but also because the 1802 made it easy to load the RAM. You
didn't need a bootstrap loader, or extensive external hardware to get the
bytes into RAM, the CPU had a pin that allowed it to put address data on
the address bus, and sequence through the memory. So you'd jam the data
in, press a button, and the next address in RAM would be waiting. Really
useful for remote use, you don't waste address space on ROM, yet if
anything fails (like bad programming or even scrambled contents of RAM,
you can reload it remotely. The fact that the 1802 was CMOS at a time
when few or no CPUs were likely helped too.
There was the ever popular Cosmac Elf in Popular Electronics in the summer
of 1976. At a time when the Altair 8800 wsa still relatively new, and
most home computers were large and required lots of parts, this one was
really simple and you could load it up right away, without needing to know
software or have the ability to write an EPROM. Since it was CMOS, you
could live without buffering or much buffering so long as you used low
power RAM. There was even battery backup on the RAM, so it would keep the
program even when you turned off the computer.
Of course, for use where radiation may cause a problem, it's not just the
CPU. RAM can be affected by radiation, someone like Forest Mims once
wrote about experiments with RAM and an available source of low level
radiation.
And a check shows that there are more recent CPUs than the 1802 that
are radiation hardened. I have no idea why the 1802 was, if it wsa
deliberate or incidental, but clearly it requires some effort and it's not
worth it doing it for every CPU. The 1802 probably gets remembered
because once upon a time CPUs in space were so novel that it would be
mentioned, and passed around. Nobody remembers what came later. Indeed,
one can remember stories of Shuttle pilots taking HP calculators into
space, and how the Shuttle early on had a Grid portable computer aboard,
but nobody talks of what was used later, it becoming commonplace and thus
not worth mentioning. Of course it should be interesting, if there was a
venue for such articles, since computers are a lot fancier than 30 years
ago, yet somehow they are able to survive in space.
Michael