modbus rtu slave not responding to request and C-ERR light coming on slave

Question

Situation I have a oriental motors LSD-KD Stepper motor driver, I'm connecting Through a PC -> USB -> RS232 -> RS485 -> Driver. The Driver uses RS485 Modbus RTU, and is sent with transmision speed of 38400, databits of 8, stopbits of 1, parity of even, and slave number of 2.

Im sending trying to send out 0x02,0x06,0x02,0x4b,0x00,0x50,0xf8,0x6b which should right a register. and im not getting any response, and the C-DAT/C-ERR goes red.

I have this bit of Javascript code

var crc = require('crc');
var SerialPort = require("serialport").SerialPort
var serialPort = new SerialPort("/dev/cu.usbserial", {
  baudrate: 38400,
  databits: 8,
  stopbits: 1,
  parity: 'even'
});

var buff = new Buffer([0x02,0x06,0x02,0x4b,0x00,0x50,0xf8,0x6b]);

console.assert(crc.crc16modbus(buff) == 0);

serialPort.open(function () {

   serialPort.on('data', function(data) {
      console.log("recieving:", data);
    });

  setInterval(function() {
    console.log("writing", buff)
   serialPort.write(buff);
  },1000);

});

When running the code I see:

writing <Buffer 02 06 02 4b 00 50 f8 6b>
recieving: <Buffer 02>
recieving: <Buffer 06>
recieving: <Buffer 02>
recieving: <Buffer 4b>
recieving: <Buffer 00>
recieving: <Buffer 50>
recieving: <Buffer f8>
recieving: <Buffer 6b>

which is excepted as the RS485 has an echo. but im not receiving any thing back from the slave.

EDIT: more on the configuration. on the RS232 <-> RS485 convertor its set to 'T.ON R.ON' and 'DCE' it is this device. a device page.

on the driver it is set as so:

SW1 is set to 2, SW1 corresponds to slave number

SW2 is set to 2, SW2 with a value of two indicates a transmission rate of 38400

SW3 is set to '1: off, 2: on, 3: off, 4: on'

 No.1: Set the address number, this causes the slave address to be 16 values higher
 No.2: Set the protocol, this sets it to use the ModBus Protocol
 No.3: Not used 
 No.4: Set the termination resistor (120 Ω)

Output port of RS232 <-> RS485 convertor is connected to driver. the output port is also connect to the input port of the converter. hence the echo.