Interfacing (DSI, CSI, I2C, etc.) • Re: How to change RTS pin in CM5 overlay file

Hi,

I have followed your advice and DI and RO are pulled HIGH and DE/!RE are shorted and pulled LOW on the next version of my prototype. I have also replaced the CM5 to account for possibly damaged GPIO pins with the 5V version.

I am using the following wiring:
RO - GPIO15 (pull-up 10K to 3.3V)
DE/!RE - GPIO16 + GPIO17 (shorted via 0R resistor) (pull-down to GND)
DI - GPIO14 (pull-up 10K to 3.3V)

To confirm the basic config: I am using UART0 on the RaspCM5, I have added the following to my config.txt:I am getting a serial port ttyAMA10, which is also mapped correctly to serial0:Communication is somehow still not working. I have connected a sensor that I know is working properly on other devices and I cannot connect via the exact same parameters through the CM5 + ISL32455EIBZ-T setup. I am also using the exact same python script for reading out the sensor, except that I have changed from COM6 on Windows to /dev/ttyAMA10 on Linux. I also swapped A/B lines on the sensor to account for miss wiring on that end - without success.

Moreover, I have shorted A/B lines to attempt a looped communication to see whether the ISL32455EIBZ-T is working properly, I cannot receive any respose.

This is the config of the pins:One thing I observed:
If GPIO 16 is set to low, and I confirm on GPIO16 and 17 is 0V, AND GPIO15 is set LOW, then GPIO 15 has 0.7V. Why is it 0.7V - should it not be 0V when set to LOW? Maybe there is a problem here?
If GPIO15 is driven high or configured as an input it has 3.3V.

I have tried sending via a python script that controls DE/!RE via software.
Upon transmission (when I set DE/RE) manually high before I send something on the bus I do not observe any change in voltage on GPIO14/15, they always remain at 3.294V, maybe it is too quick for my multimeter to react.
Looping over my send command gives me a voltage of 3.278 on DE/RE. I can see with " pinctrl poll 14-17" that the state of GPIO16 is changing all the time, therefore I assume that the multimeter averages over the measurements and since it is sending most of the time I see 3.278.

For that reason I assume that DE/RE control is working correctly.

Another thing I have attempted is to use CTS/RTS via Then, GPIO16 and GPIO17 are assigned CTS/RTS functionality. But communication is still not possible.


Do you have any more ideas for troubleshooting this setup?

What am I doing wrong?

Thanks,
Nils

Statistics: Posted by Nils1234 — Fri Jun 06, 2025 1:01 pm

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