Secondary UART interfers with GPIO Pin: Write is not possible while changing the state of GPIO Pin

[Space-Dream-42]

Hello,

Firmware Version: 11721
Product: Digi XBee 3 Low-Power LTE-M/NB-IoT
Part number: XB3-C-GM1-UT-XXX

When I run this code everything is fine and the Module does write the string "TEST" on the secondary UART TX Pin (physical Pin: 11) as excepted.

import time
from machine import UART, Pin
from xbee import relay
import xbee

uart = UART(1, baudrate=19200, bits=8, parity=None, stop=1)

while True:
    uart.write("TEST")
    time.sleep(3)

However, when I also try to define and use the GPIO Pin P0 (Physical Pin: 6), then the module doesn't write the string "TEST" anymore to the secondary UART TX pin. I validated that by measuring the Pin with an oscilloscope, there was no signal. uart.write is silently doing nothing:

import time
from machine import UART, Pin
from xbee import relay
import xbee

uart = UART(1, baudrate=19200, bits=8, parity=None, stop=1)

led = Pin("P0", Pin.OUT, value=0) # HW_Pin: 6

led.value(1)

while True:
    uart.write("TEST")
    time.sleep(3)

This is unexpected behaviour. What I would at least to expect is an exception. Is it possible to make secondary UART and the GPIO Pin working concurrently?

best regards from Berlin!

[mikewadsten]

Hi Armin,

Thank you for the report! I have filed a ticket internally to look into this and try to reproduce the finding. If what you've reported is found to be reproducible, I would agree that it is unexpected behavior; at first glance I do not know why manipulating DIO10, a pin unrelated to the Secondary UART, would cause the behavior you see.

In the meantime, can you tell me what sort of hardware or development board you are using? Is it possible that some external hardware is pulling pin 11 (high or low) when DIO10 is high?

For future reference, please know that this GitHub issue tracker is not monitored by Digi technical support, and if you encounter any more problems with built-in functionality like this, you should post on the Digi Support Forum.

[Space-Dream-42]

Hey Mike,

thank you for your answer. I thought it would be a concern of the micro python interpreter that's why I wrote the issue here, but thank you for the hint! Although you going to answer here when the problem is resolved?

Development board: SparkFun Digi XBee® Explorer USB-C

Is it possible that some external hardware is pulling pin 11 (high or low) when DIO10 is high?
I don't think so. I couldn't observe that when I measured correctly.