I have worked with Arduino UNO but recently I bought a new Arduino Pro mini 5v 16M and a CH340G converter to work with. I have searched google to connect pins but I found examples that explains this way :
Converter RDX to Arduino Pro Mini TXO
Converter TDX to Arduino Pro Mini RXI
My problem is that my Arduino Pro Mini (328p) has pins TXD and RXD (not RXI , not TXO) or maybe I have no knowledge about TX,RX, IN and OUT.
Can someone please help me to connect these wires?

2 Answers 2


Generally, lines with names like TX, TXO, and TDX are for serial-data transmit, and lines with names like RX, RXI, and RDX are for serial-data receive.

Connect transmit on the CH340G board to receive on the Pro Mini, and vice versa.

For typical serial-converter programmers (I don't know specifically about the CH340) you need to connect CTS (Clear to Send, if the programmer has it) to the pin next to BLK on the Pro Mini, and RTS to GRN (DTR). The RTS-to-DTR (Request to Send, Data Terminal Ready) connection lets the programmer auto-reset the Pro Mini to start programming.

See yourduino.com's ProMiniPinout.png diagram.

  • Thank you very much for this detailed answer. RTS-to-DTR connection helped me so much :) May 17, 2016 at 23:47

try reversing the tx/rx lines, if the PRO Mini and serial adapter are chinese, you may want to try using your UNO as ISP programmer. See here for a hint/ex: https://www.arduino.cc/en/Tutorial/ArduinoISP

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