The USCI is reset by a PUC or by setting the UCSWRST bit. After a PUC,  the UCSWRST bit is automatically set, keeping the USCI in a reset condition.

To select I2C operation, the UCMODEx bits must be set to 11. After module initialization, it is ready for transmitting or receiving operation. Clearing UCSWRST releases the USCI for operation.

To avoid unpredictable behavior, configure or reconfigure the USCI module only when UCSWRST is set. Setting UCSWRST in I2C mode has the following effects:

  • I2C communication stops.
  • SDA and SCL are high impedance.
  • UCBxI2CSTAT, bits 6–0 are cleared.
  • Registers UCBxIE and UCBxIFG are cleared.
  • All other bits and registers remain unchanged.