UART A Communication using dtr signal

I am looking to write and read data using DTR signal (RS485) from UART A port.
Please check below given settings :

c# Code part :

serialPort1.PortName = "COM1";
serialPort1.BaudRate = 9600;
serialPort1.ReadTimeout = 2000;
if (!serialPort1.IsOpen)
   serialPort1.Open();
serialPort1.DtrEnable = true;
serialPort1.Write(sendbytes, 0, sendbytes.Length);
serialPort1.ReadTimeout = 2000;
byte[] readBytes = new byte[10];
serialPort1.DtrEnable = false;
Thread.Sleep(500);
serialPort1.Read(readBytes, 0, readBytes.Length);
serialPort1.DtrEnable = true;

Error : The operation has timed-out.

Registery setting for VF50 module :

HKEY_LOCAL_MACHINE\Drivers\BuitIn\UARTA
default setting nothing changes

Note : Same code is running quite ok on IMX6 module

Registory Settings for IMX6 :

HKEY_LOCAL_MACHINE\Drivers\BuitIn\COM1
RTSToggleAlwaysOn = dword:1 
RTSPol = dword:1
RTSPin = dword:27
TXPin = dword:35
RXPin = dword:33
CTSPin = dword:25
DTRPin = dword:23
DSRPin = dword:29

please help if there is any pin or function code need to add in UART_A registry setting for DTR toggle or may be its required some extra code for DTR toggle using GPIO

We are using 485 transreceiver MAX13442 and 23 sodimm pin for DTR.
DTR is connected to pins RE and DE of MAX13442 transreceive.

Usually, the RTS signal is used to toggle RS485, as described here:

http://developer.toradex.com/knowledge-base/rs485

and RTSToggleAlwaysOn setting is supported also on Vybrid.
If you need to use DTR you need to configure what pin is used for DTR signal as described here:

http://developer.toradex.com/knowledge-base/serial-port-registry-settings#Colibri_VFxx_Registry_Settings

And then you should be able to toggle it in your code.