I've got some equipment here that has RS422 serial on it - i.e. it uses
differential signal pairs rather than RS232's reference against ground.
Question is, can I wire up a cable so that I can use an RS232 terminal with
this RS422 equipment? (running over a short distance)
Looking at the schematics, I think it's possible, with signals mapping to:
TXD- no connection?
BSY- no connection
... but I don't know if I should ground TXD-, or indeed one web site I saw
suggested that TXD- should be used as the signal and TXD+ is actually the
reference. I suspect that one or other should be left floating and the other
pin of the pair forms the 'real' TXD in RS232-speak.
Obviously I need to swap signals for communications to work (RX -> TX, TX ->
RX etc.) :-)
CTS- and BUSY- aren't actually brought out to the comms port on the equipment
at all; CTS- is currently jumpered to ground internally, and BUSY- is left
floating and brought to a test point on the PCB.
RXD- is also currently jumpered to ground, which suggests that I can indeed
connect TX on the RS232 terminal to RXD+ on the equipment and expect that side
of things to work - I'm just not sure what I need to do with the TXD+/TXD-
signal pair (which one actually connects to RX on the terminal end)
(the actual comms chip is a 6551A, then the receiver for RXD and CTS is a
26LS32 and the driver for TXD and BSY is 26LS30)