4 ms·
As far as I understand there were actually lots of different "RS232" variations. Nowadays I believe everything is asynchronous, which makes many of the pins tha
by jchw 4y ago
As far as I understand there were actually lots of different "RS232" variations. Nowadays I believe everything is asynchronous, which makes many of the pins that used to be connected redundant; lines that carried things like clock or additional flow control related signals. I'm not an expert, I just noticed this looking at old NEC computers.
- retrac 4y agoRS232 itself is a well-defined spec. But you're right. An lot of equipment existed that was only vaguely RS232 compatible. Some of it even predates RS232. For example, the old electromechanical teletype machines send and receive something close enough to RS232 line signalling that you can connect them to a modern computer's RS232 port, if you wire up a tiny analog circuit to convert from telegraph-style current impulses to RS232-style voltage levels. Just set the UART to 50 bps with 5 bit data and 2 stop bits. And don't send anything too soon after a carriage return! Not all UARTs can handle those settings, but that's why such options were in terminal programs back in the day.
- ghaff 4y agoDB25 ports were also used for different (although related) standards like RS-422.
- dfox 4y agoOne particular thing to note is that on anything IBM PC related the DB25 RS-232 connector has the wrong gender (apparently so that it can be connected directly to modem with DB25 extension cable instead of 1:1 M-M cable as would be expected for RS-232).