I measured my SCL at 1 MHz using an HP logic analyzer. It should have seen 100 KHz. I see the Start pattern, the address followed by a 1 which means read. No ACK from the slave which is to be expected because the clock is way too fast. A 6 uS wait and then a valid Stop pattern. See attached picture.
Starting with button.ino (from Adafruit and uses the MCP23017) I worked my way down through Wire to twi plus matched it up with the ATmega32U4 spec sheet. I see nothing wrong.
I then modified the twi_init() code with constants that should have changed the bit rate as per the equation in the spec sheet (section 20.5.2). No joy. I intentionally left off a ";" in twi_init() and the compiler found it so I was changing the correct file.
I have been asking both on the Sparkfun and Adafruit forums with no response.
Has anyone successfully used the I2C interface on the Pro Micro or on an ATmega32U4?
Thanks in advance!
Rick
