The disable I2C user bus program program is a simple “rescue program”, that you can upload to your RFzero, in case you uploaded a program that uses I2C, but you forgot to connect the I2C pull-up resistors.

All the program does is to set the I2C addresses of the SX1509,  MCP23017 and PCF8574 port expanders to zero (0) in the EEPROM. Thus when you upload the program, that uses the I2C user bus, it doesn’t try to enable or use the I2C user bus.

If you connect a serial monitor program to the USB port on the RFzero you will see if the operation was successful or not.

The output on the serial monitor after a successful operation.

If the uploading fails try to upload again and be prepared to double click the reset button on the RFzero when the upload is about to start. You may have to try this a couple of times.