I am trying to make a differential I2C bus signal that is compatible with SparkFun's QWIIC.
- OK: convert the standard I2C's SDA and SCL to TX/RX lines using P82B96D
- NOT WORKING: convert TX/RX to differential signals using PCA82C251
Below is the schematic for transforming between the TX/RX signal and the differential signal.
And this is the waveform at SDA1_TX line when the microcontroller is trying to search the bus for a specific address:
As the waveform shows, the SDA1_TX is correctly outputting a 5 V pulse. The other SCL1_TX was also outputting a clock signal in the same way to another PCA82C251, but the differential lines are not outputting any signal. They are just kept at a steady 2.5 V without changing.
What could be causing this problem?
Full schematic of the I2C to dI2C conversion part: