I need to connect the TRB255 to an ARM computer with a 2-wires RS485 connection. I short-circuited R+/D+ and R-/D- as per your manual.
Now I'm trying to send AT commands from the ARM computer but I get no answer from the modem. I'm simply doing an
echo AT > /dev/ttyS1
and, on another terminal,
Current configuration is 9600, databits 8, parity None stopbits 1, flow control None, serial type Console, Full Duplex OFF