UART with open drain

[bixb922]

Is it possible to configure a UART with open drain for output on the ESP32-S3? How can that be achieved?

[robert-hh]

Technically it may be possible, to reconfigure the Pin output driver in machine_uart.c after the UART has been configured. But this is not implemented. Until then, you can go for external hardware solution of a wired NOR built with shottky diodes and a pull-up resistor.

[bixb922]

Thank you!

[bixb922]

Finally the solution is simple. For example, this works on the ESP32/ESP32-S3:

from machine import Pin, UART
uart = UART(1, baudrate=9600, tx=Pin(10, mode=Pin.OPEN_DRAIN), rx=9  )

You can either specify a pin number, i.e. tx=10 or pass a Pin object. I measured the output and the open drain and drive= parameters work as specified for the UART.

[robert-hh]

That's indeed an easy way. I verified that by measuring the current from the output to GND. In "normal" mode, it' 50mA, when set to OPEN_DRAIN, it's about 0. Some Pins like 2, 4, 5 have an OPEN_DRAIN current of about 400µA. But that is not related to the Pin setting.

[bixb922]

Thanks! I had tested too. drain= also works well. I am trying to submit a PR updating the docs.