TTL terminal connections (Nullmodem)
How to connect a USB to TTL converter to a TTL device?
Basically there are only 3 connections that matter
Transmit : TX
Connect the TX from the converter to the RX of the device you want to communicate with and vice versa, connect the TX from the device to the RX of the converter. And also connect the GND of both devices together. The signals of the TX are being read respectively to the GND (0 Volt) And that's the basics of how this system works.