Does RS422/RS485 work on Advantech PCM-5820?

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I just received an unpleasant surprise when trying to use differential
serial on the Advantech PCM-5820. The system has jumpers for the
second serial port; RS232, RS422 or RS485. In either RS422 or RS485
mode, I see no activity at all on the TxD+/- pins.

My software is asserting DTR and RTS, so I don't know what else I
could possibly do to enable the drivers (and they should always be
enabled in RS422 mode anyway, right?) I know I'm talking to the right
I/O port and IRQ because when I jumper it back to RS232 I see activity
on the TxD pin. I'm giving the board both +5 and +12, so it can't be
missing an input voltage. I have ritually waved a White Castle
hamburger over the machine and threatened it with a steak knife, with
no discernible effect.

I have jury-rigged the system to work on the port in RS232 mode by
connecting Rx- on my DCE to gnd and Rx+ to TxD on the DTE, but
although this proves my device is working, it is not deployable.

Any ideas? Does this feature even work? Advantech's stellar
documentation doesn't tell you how to use it at all, they just give
you the pinout of the 14-pin connector on the board. You have to pull
off the backshell to work out which pins go where on the "RS422/485"
DB9M.

Re: Does RS422/RS485 work on Advantech PCM-5820?
I have a 5823, but I thought the com2 had a standard serial output connector
for 232 and a seperate header for RS485.
I'd have to check though.


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Re: Does RS422/RS485 work on Advantech PCM-5820?
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The 5820 has a 14-pin 2mm (7x2) header for COM2, and the board comes
with a cable that has two DE9Ms on it; one for RS232, and one for
RS422/485.

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