TTL to RS422


Firstly, sorry for my English is not my native language.

Regarding my question, I work on an Arduino project on which I have to use an RS422 link.
The microcontroller only coming out of the UART TTL, I must turn this nivau TTL to RS232 converter then I utiliose 232/422 to drive my peripheral.

The connection TTL> 232 is made with a MAX232 (Pololu 23201a)
I supplies 5v and I connect Rx and Tx. (and GND of course)
Then I plug in a standard RS232/RS422 converter, but this arrangement does not work.
If I replace the MAX232 with a standard RS232 PC connection, everything works perfectly with HyperTerminal connection.
So I guess it does not come from my wiring.

If I do not use my converter 232/422 and I loop the Tx and Rx output Max232 (Pololu 23201a) I have sent the return of give on either HyperTerminal Serial Monitor is on the Arduino IDE.

It is therefore obvious that the PC sends a signal that the microcontroller does not send or I miss a signal to open the side RS422 connection.

Have you ever used this type of link (TTL> RS422) and if so, how did you handle this setup?

Thank you for your help


Hello, astondb8.

The Pololu 23201a Serial Adapter does NOT have a MAX232 chip on it. The MAX232 serves a similar purpose, but it is not what we put on our serial adapter.

Please clarify what TTL-to-RS232 adapter you have. Do you have a Pololu 23201a Serial Adapter?

Pololu 23201a Serial Adapter

Please tell me more about your wiring. What did you connect the Arduino’s RX to? What did you connect the Arduino’s TX to? It sounds like you are successfully powering the adapter, but just in case: how you are supplying 5V to the serial adapter?

I don’t know much about RS-422 and I know nothing about this peripheral you are connecting to. Is it possible that the peripheral requires a particular handshaking line to be in a particular state before it will turn on and communicate? Typical terminal programs will do things with the DTR and RTS line when you open a connection. I recommend doing some experiments with Br@y Terminal. It allows you to control the RTS and DTR lines, so you can see if those have an effect. Another thing you could to is measure the voltages on different pins on the standard PC RS-232 output (which works) and compare those to the voltages on the output of your serial adapter.