"muktabh" <m_anchlia@hotmail.com> wrote in message 
news:cdGdnb0bHvpf9zbanZ2dnUVZ_sGvnZ2d@giganews.com...
> Hi,
> I have an advantech PCM-4153 board with 4 com ports. The user guide 
> says
> 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 
> jumper
> to switch from rs232 to rs485. Will I need to change the serial comm 
> code
> 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 
> read
> in the output in using hyperterminal.
>
> Will the above work?

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
http://www.fivetrees.com 

Hi,
I have an advantech PCM-4153 board with 4 com ports. The user guide says
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 jumper
to switch from rs232 to rs485. Will I need to change the serial comm code
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 read
in the output in using hyperterminal. 

Will the above work?

Thanks...