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RS 485 on advantech PCM-4153 board

Hi, I have an advantech PCM-4153 board with 4 com ports. The user guide say port 2 can be configured as a RS485 port. I have a few doubts. I am using linux on this board. Will I need special drivers to use RS485 (the board uses sch3112 chip for IO) The user guide says to set a jumpe to switch from rs232 to rs485. Will I need to change the serial comm cod too? Is it OK if i do this:

1) COM 2 is configured as a serial port right now. 2) I dont change the code, just set the jumper to RS485. 3) I run the code, connect COM 2 to a RS485 to RS232 convertor, and rea in the output in using hyperterminal.

Will the above work?

Thanks...

Reply to
muktabh
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I don't know that specific board (have dealt with other PCM cards), but typically RS-485 needs some line discipline. Strictly speaking, RS-485 is half-duplex (3-wire: 2 for comms, 1 for ground); you either tx, or you rx. Not both. Something (often the RTS output) needs to enable/disable the drivers.

Again strictly speaking, the 5-wire version (full duplex) is RS-422, but the distinction is getting a bit blurred - people talk about FDX RS-485 links these days (which is mostly ok - RS-485 drivers are way more robust than RS-422 drivers). If your board has a distinct pair of RS-485 outputs and another distinct pair of inputs, you'll be fine. Otherwise, you'll need to enable the drivers while you tx (and for a short while afterwards, long enough for the last character to leave), and disable the drivers when you rx or when you're idle.

HTH,

Steve

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Reply to
Steve at fivetrees

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