New guy here and I apologize in advance if I'm breaking etiquette. I submitted this to a prior thread (https://www.raspberrypi.org/forums/view ... x&start=50), but this strikes me as a slightly different problem and so I'm starting a new one. My issue is related to the SC16IS752 expansion hat. I'm trying to construct a simple device to test upwards of 17 serial connections quickly and thought the SC16IS752 would be the answer. I've read every thread I can find on the topic and while no doubt a ton of things have been ironed out I haven't found a solution to this particular hiccup.
My setup - Pi Zero W w/ full Buster update + rpi update. I have two SC16IS752 expansion hats currently. The two hats are addressed for 0x48 and 0x49. The additional serial ports appear in 'ls /dev/ttySC*' as ttySC0-3. They are enabled via the overlay entry of 'dtoverlay=sc16is752-i2c,int_pin=XX,addr=0xXX', where my int_pins used are 23 and 24. When running a 'i2cdetect -y 1' they both appear as UU in their respective columns. No other I2C device is attached.
The problem - full functionality follows which ever overlay is assigned int_pin=24. While I can Tx on the other board, (as checked by sending messages to the AMA0 port), I cannot receive anything. While looking at the signal with a meter, I can see the IRQ leg is high when I do not have a terminal open watching it. As soon as I establish a miniterm or puTTY session, the IRQ falls low and stays low. Through a fluke occurrence I noticed that if I apply and disconnect a load to the Pi's 5v bus I can inadvertently trigger the IRQ to go high which causes messages to appear, but then the IRQ goes back low a moment later and I'm back to where I was. I ran a 'gpio readall' to get a list of default low pins and have tried several with no success. As I mentioned earlier, I can move int_pin=24 between 0x48 and 0x49 and which ever board has it, works perfectly so I don't feel like its a hardware issue.
Any help with this would be greatly appreciated. Thank you!