Modbus between PC and Laptop using USB-A to USB-B Cable

[curious_mal]

Hi.
I am trying to set up a control system on an Arduino Mega 2560. As part of this a PC (master) needs to read/write to coils and holding registers on the Arduino.
To keep wiring simple I have connected the two with a standard serial USB-A to USB-B Cable.

I have tried to get the system working using the following libraries & examples:

1. GitHub - epsilonrt/modbus-serial: A library that allows your Arduino to communicate via Modbus protocol, acting as a slave. Over serial line implementation (OSI 2/OSI 1)
   modbus-serial/examples/Lamp/Lamp.ino at master · epsilonrt/modbus-serial · GitHub
   Lamp.ino (1.4 KB)

Arduino_Modbus_RTU_example.ino (668 Bytes)

3. GitHub - CMB27/ModbusRTUSlave: This is an Arduino library that implements the slave/server logic of the Modbus RTU protocol.
   ModbusRTUSlaveExample.ino (4.6 KB)

On the PC I have installed Modscan. I match the baud rate, and Device ID, connect, and Poll the Arduino but do not receive any 'Valid Slave Responses' using these programs.

There are lots of discussions/examples about using RS485 (eg https://www.youtube.com/watch?v=zTanigwP5ow&ab_channel=MYSONACADEMY%26TECHNOLOGY) but I can't find any about this simple issue.

Has anyone been successful in doing this?
Do I need additional hardware, or wiring changes?

Thanks in advance for your help.

[vishnu_raut_001818]

I am facing same issue do not receive any 'Valid Slave Responses please give any solution....