What kind of USB to RS485 converter are you using? If it is a Trinamic USB-2-485, the connections should be as follows:
PD-013 pin 15 (RS485+) to pin 7 of the USB-2-485
PD-013 pin 16 (RS485-) to pin 2 of the USB-2-485
optional GND (pin 14) to pin 3 of the USB-2-485.
The Trinamic USB-2-485 is already equipped with a RS485 termination network, so there is no needto add those resistors then. But with most other converters this is needed (for example we have also tried an USB to RS485 converter cable from FTDI).
Connection speed is 9600 baud, 8 data bits, one stop bit, no parity. After opening the connection, first press CR some times. Then try to enter e.g. AX and hit CR to display the firmware revision number.