UART Questions

[cebersp]

1. I have to invert an UART output- How can I do this?

Code: Select all

# Test UART for Midi Input
# https://docs.micropython.org/en/latest/library/machine.UART.html
import utime
from machine import UART, Pin
rxPin=Pin(1,Pin.IN,Pin.PULL_UP)
txPin=Pin(0,Pin.OUT)
#uart=UART(0,31250, rx=rxPin, tx=txPin, invert=UART.INV_TX) # does not work       #init with given baudrate
uart=UART(0,31250, rx=rxPin, tx=txPin) # does work       #init with given baudrate
while True:
    uart.write("hello")     #write "hello"
    utime.sleep(1)

2. Is there an example, how to use interrupts with UART?

Many thanks in advance, Christof

[Roberthh]

At the rp2040 port the invert keyword is not supported. Maybe yet. So you have to use an external inverter. A single 2n7000 transistor + resistor may be sufficient, or a CMOS inverter (e.g. 74hc04). Or you could try one of the PIO examples for UART, where you can control the pin levels yourself.

[cebersp]

Thanks!
I will use hardware then.

[dhylands]

There is a uart _tx PIO example for the pico. You could modify this to produce an inverted uart output.

[fdufnews]

In the datasheet, chapter 2.19 table 296 concerning GPIOs, there are GPIOx_CTRL registers (one for each GPIO) in wich you can change the behavior of the GPIO. The OUTOVER bits allow to modify the polarity of the output.

[cebersp]

Setting registers: Yes, I had seen, that the hardware can do it. I have not yet done inline assembler in MicroPython, so I don't know how to access the registers directly.

PIO: Well, I can understand some of the PIO examples, but I do not feel able to make this quickly...

In my case, this serial line is going to an optocoupler for Midi, so here it is really simple to do it with hardware...
Thanks!

[Roberthh]

I have made a PR for setting invert mode. https://github.com/micropython/micropython/pull/6870
It provides the timeout setting as well.