read data from controller via RS485 Modbus rtu Arduino
I can't say if this is your problem or not but I don't like this bit of code:

   RS485Serial.write(request, sizeof(request));

   digitalWrite(Pin13LED, LOW);  
   delay(10);
   digitalWrite(SSerialTxControl, RS485Receive);


You're sending the request then waiting 10ms and switching to receive mode.  That might be enough of a delay, but it's hard to say (best case, 960Bps at 9600 baud gives about 1ms per byte, which is 8ms for the request, but with software serial it may not be that simple).

Instead you should be using the flush method of the Stream class to wait for the data to be transmitted:

   RS485Serial.write(request, sizeof(request));

   digitalWrite(Pin13LED, LOW);  
   RS485Serial.flush();
   digitalWrite(SSerialTxControl, RS485Receive);