re reply#11, there is no such thing as a software serial monitor.
Sorry to confuse you, but when I was saying about using Rx Tx and Serial Monitor, I was trying to say that my SoftwareSerial method doesn't work, so I have gone back to Hardware Serial, removing SoftwareSerial from the picture.
Your hand drawing does not agree with the pic in the link.
Actually I was asking you, whether I should go with method that they have used in that link, so my drawing is not built according to that.
Get rid of the useless delays in the program shown in the .jpg appended to reply #15.
The delay(50) is because PLC is sending data at every 50 milliseconds. And I send just ONE Character from PLC so ARDUINO should perfectly match with that.
The delay(1000) is because I was getting print statements in loop to quick to understand. So for now it is definitely useless. And I will get rid of them.
Then bidirectional character transmission should work, but if not, try swapping the wires connected to pins 2 & 3.
I did try swapping the pins. I think I'm frustrating you guys by complicating my replies. I'll try to keep it simple onwards.
And I will further be uploading the code after disconnecting the RS232 - TTL converter from Arduino.