Serial communication with a slave board

Hello Guys,

I have a board that is analyzing a modulator and is controlled with computer by opening a port (baud-rate: 19200). It is connected to a computer by a mini usb cable, and has an interface (I use Tera Term for opening a port), such as you can set the voltage limits it should give by writing "vmin 05.00" to the serial port.

It works fine when I change the features through computer connection or using MATLAB to read and write the data. However, when I try using an Arduino Nano to send serial data it fails. Such as using the code below;

void setup() {

  Serial.println("VMIN 0");
  Serial.println("VMAX 11");

I believe that is caused by trying a slave to slave connection. So somehow I guess I should make Arduino master. So far, I tried connecting a PL2303 to the board, PL2303's Rx, Tx, Power, Gnd connections are made with Arduino. I also tried connecting both directly by cable using a usb to mini usb converter.
I ask for your help on how can I make them communicate with each other.

Thanks in advance.

It's probably an error in the part of the code that is missing.Are you using the software serial in the Nano program? I understand it can't function at the speed you posted.