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P3H2840 debugging issues consultation

Currently, I'm debugging based on the official P3H2840 demo and found that the temperature sensor readings on the demo differ between I2C and I3C modes (as shown in the image below). Is this normal?

Re: p3h2840调试问题咨询

Hi,

The 0xff second byte you are seeing on every I3C mode register read is not correct and points to a hub configuration issue. For reference, the on-board temperature sensors on the P3H2x4xHN-ARD are NXP P3T1755DP devices, which are fully I3C-capable, so the readings should be identical in both modes once the hub is correctly set up.

Please check the following three items:

1. Dynamic address assignment — The P3T1755DP powers up in I2C mode and must receive a dynamic address (via ENTDAA, SETAASA, or SETDASA) before I3C private transfers will work. If i3c_xfer is called before this step completes, the device cannot respond correctly to I3C frames, and the second byte will read as 0xff. Confirm that the address assignment CCC ran successfully and that 0x4c is the assigned dynamic address.

2. Burst Length enable — REG#17[6] (BL_ENABLE) — If this bit is set, the I3C write phase must include a Burst Length byte after the register pointer. If your i3c_xfer call sends only 1 write byte (register address), the hub receives an incomplete frame and the read response is misaligned, causing 0xff on the second byte. Please read back REG#17 and confirm whether bit 6 is set. If it is, either add the BL byte to your write payload or clear BL_ENABLE if it is not needed.

3. Target port VCCIO — REG#22 — In I3C mode the target port uses push-pull drive levels referenced to the VCCIO setting in REG#22. If this does not match the actual P3T1755DP supply voltage, data bytes transferred in push-pull mode can be corrupted. Please confirm that REG#22 reflects the correct operating voltage for the target port the sensor is connected to.

Re: p3h2840调试问题咨询Thank you for your reply. It seemed the device didn't support SETAASA. After changing it to SETDASA and entering the I3C interface, it worked correctly. Thank you for your support.