On 2025-01-31 4:25 a.m., Frank Leonhardt via cctalk wrote:
A couple of points you might like to consider, which you may already
know but stuff you've said above doesn't spell it out:
RS232 is not serial - make yourself clear. Before RS232 the same data
format was used in current loop (often 20mA or 60mA).
RS232 (AKA V.24) is only understandable when you realise it was
connecting a terminal (or later computer) to a modem. It's very
specific, yet like most technology has been subverted for other
purposes. I've kept at last one full RS232 modem in my loft (it was
government surplus, and I used to to run a BBS in 1980). Things got
weird later, particularly with the Hayes Smartmodem, but modems were
dumb devices. The lines went straight through. There were two
oscillators (for FM) and the appropriate one was switched in by the TX
line being high or low. Likewise the data separator looked for a high or
low tone and flipped RX between -12V and +12V. These were all individual
boards!
I always wondered why one needed a 25 pin connector?
Now every thing seems to be just 3 wire TTL.
Before RS232, how many wires where needed for the current loop
and did they have standard connector?
I can see 2 wire pairs, and ground.
