write data to a register using wire library

Just commenting out the write portion, ie, Wire.beginTransmission(0x74) Serial.print('Return data length doesn't match : ') Serial.println(requestDataLength) The code is fairly straightforward: int UpbeatLabs_MCP39F521::registerReadNBytes(int addressHigh, int addressLow, I’m not sure definitively if there is any internal pullup enabled on the I2C pins of the Particle Photon (the older version), and if so, how I may be able to disable the pullup (seeing as pinMode above has no effect when using Wire library). I thought I2C has internal pullups enabled by default, and I also tried to set pinMode differently to disable any internal pullups, but getPinMode always returns 5. Used internally for Alternate Function Output Drain(I2C etc). setting the pinMode on the I2C pins (to disable any pullups) seems to have no effect - getPinMode always returns 5 (AF_OUTPUT_DRAIN) The comments say I’ve tried with external pullups (above the 10k of the bidirectional level shifters) - 2k, 10k, no pullups. If I pull the SCL wire and reconnect it, I can get a response (whose data also looks ok), but subsequent calls fail in the same way as described above (Wire.available gives 0), which seems to suggest issues with pulling down the signal to low? Logic analyzer shows proper message being sent by Particle, but then there’s no response. After writing to some registers to request data, I call Wire.requestFrom to read the data, followed by Wire.available(), which returns 0. However, with the Particle Photon (running DeviceOS 3.3.0), I’m not getting any data response from the device. The board is powered by 3.3v and the MCU side has a VIN for logic level voltage to pull up to - 3.3v or 5v. The device works fine with Arduino Uno (5v), Arduino Pro Mini 3.3v, Raspberry Pi (3.3v with an equivalent Python library), Arduino Nano 33 BLE Sense, Raspberry Pi Pico (3.3v) with CircuitPython. The board has bidirectional level shifters for the SDA/SCL lines using BSS138. I have an Arduino library called UpbeatLabs_MCP39F521 that I ported to Particle. Wattson and is based on Microchip’s MCP39F521.

Write data to a register using wire library