I'm debugging a single I2C master (Raspberry Pi Compute Module) connected to a single slave (a TLV320AIC23B audio codec on separate board)
They are connected by 3" jumper wires (4 wires SDA, SCL, PWR, GND). There are 4k7 pull up resistors on the master side.
About 20% of the time the slave doesn't successfully pull the line low for ACK and I can observe the following pulse in the scope:
And up close:
Does anyone know what would cause a condition like this?
When I add 220 Ohm series resistors to SCL and SDA at the slave side, the problem goes away completely, but trying to understand why.