Raspberry Pi - UART - disable TX and enable RX in program C

Question

I need connect my raspberry pi 4 model b with a servo via UART, but it is possible only via 1 wire. That means I must connect pin TX and RX together. In order to do so, I must have a way how to manually disable only TX or RX in my C program.

I am able to easily disable RX thanks to termios.h library, but I didn't find any way how to disable TX.

I was trying to disable it through this

tcflow(fd_myUART, TCOOFF); // it should suspend output

But that didn't work, so I thought that maybe if I change the pin of TX to INPUT, it will change the pin from UART to GPIO, but that didn't work either.

Do you have a way, how to do that, please?

Answer 1

First of all, just "randomly" connecting both wires is a bad idea. Below image shows how to do it better for a prototype. Slave devices are able to pull the IO line low during a read bit or a reset while the TX signal is high.

When used in this configuration, you should not disable RX nor TX. You can use "normal" UART operation.

More information can be found here (maxim integrated tutorial 214 "USING A UART TO IMPLEMENT A 1-WIRE BUS MASTER")

Answer 2

Since you will have a lot of connected slave, you should consider using a dedicated chip:

I use a DS2482S-100 over I2C.