20 Aug
2005
20 Aug
'05
8:08 p.m.
On 8/17/05, infomagic <infomagic at localisp.com> wrote:
Tony wrote:
have never seen a bit-banged RS232 (or current loop) port on a
minicomputer. Anyone know of one?
On the RCA 1802, there was an output line named "Q", and there were two
instructions that directly set and reset the line. I believe the CPU had a built-in
D-flip-flop for keeping it stable.
It's my understanding that this line was often used to drive serial output. You might
be able to locate software for any of the ELF computers that would show this use. I'll
see what I can dig up...
Except that the 1802 is most decidedly a microprocessor, not a minicomputer.
I am unaware of any mini that did bit-banged serial. There were some
DEC console ports that impacted performance (11/750, 82x0/83x0), but
they were a hardware implementation AFAIK. Perhaps HP or DG might
have an example?
-ethan