rs232rs485sharedbus
I have 2 pins and primary function should be A/B RS485, but is possible that I also put RS232 (Rx/Tx) chip on same bus and then control which one I want to use from microcontroller.
I was thinking about MAX232 and MAX481 and enabling and disabling them trough power on/off controlled by microcontroller driving transistor.
Is there any single device that does this?
It looks like the opto-cable is resuing DTR and RTS as it's own power input pins.
Your MAX3222 uses charge pumps to generate the high positive and negative voltages for signalling over RS-232.
To me, if your cable doesn't draw a lot of current, the easiest thing to do would be to connect the positive supply (DSR) to V+ (pin 3) and the negative supply (RTS) to pin 7 of the MAX3222. Voila, power.
If your cable needs more juice, you'll need to provide it by some other means (a separate power supply or charge pump).
The problem was an undocumented even parity bit required by the device I need to control (a Bentel Kyo300 alarm security panel), but even if I found which the problem was a limitation in the serial wireless modules prevents to re-generate the parity bit on the destination end-point.
Those serial-wireless adapters have, in fact, fixed serial-side configuration of 8N1... I solved buying better and configurable serial wireless modules (APC220) :)
I've learned a lot about hardware-level serial communication during this discussion so I'm happy even if I spent few more euros ;)
Best Answer
Exar has the SP331 programmable RS-232/RS-485 transceiver which may suit your needs.