Bit banger /analog modem

infomagic infomagic at
Wed Aug 17 12:35:07 CDT 2005

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...

-John M.

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