RS232 interface

The computer has two serial ports. One RS232 and one RS485. Both ports are optically isolated from the main computer circuit, but are not isolated from each other.


The RS232 port includes CTS and RTS signals in addition to TX and RX signals. The baudrate range for the RS232 port is 1200 bps ~ 921600 bps. The port is protected by high-power TVS diodes against electrical surges.

We can access this using "/dev/ttyS2" port which you can check using "ls /dev/ttyS*" command.

Hardware requirement for testing

  • RS232 to USB cable (recommended ADI-501
  • RS232 cable

Testing setup

Download the Testing Script from below mentioned link and unzip the "" file in any folder.

Connect one end of RS232 to USB cable with any laptop and other end with AG-1621 with cables as shown below.

RS232 cable pinout AG1621 Pinout
Rx RS232 - OUT
Tx RS232 - IN

Open any serial terminal application like hercules, terminal, in laptop with default configuration 115200 baud rate.

Go to AG1621_Script folder


Run modem start script

 sudo sh

If asked for password, then type "atreyo" and press enter. It starts printing output as per below screenshot.

Once Script starts running then it will ask to enter any input from "send" or "receive" which user needs to enter using keyboard.

If you are typing "send" then it will again ask to enter any string like "Hello there!" and press enter. After this check in externally connected laptop if the serial port application received same message or not.

 If you are typing "receive" then it will be wait to receive an input from other end so at that time send a string from externally connected laptop's serial port application and then check whether the same string is received in AG-1621 or not.

 If both ways receive proper string then your RS232 communication working fine.

To stop running this script press ctrl + c shortcut.