36.4.1.2 General Call Addressing Support

The I²C Specification reserves the address 0x00 as the General Call address. The General Call address is used to address all client modules connected to the bus at the same time. When a host issues a General Call, all client devices may, in theory, respond with an ACK. The General Call Enable (GCEN) bit determines whether client hardware will respond to a General Call address. When GCEN is set (GCEN = 1), client hardware will respond to a General Call with an ACK, and when GCEN is clear (GCEN = 0), the General Call is ignored, and the client responds with a NACK.

When the module receives a General Call, the ADRIF bit is set and the address is stored in I2CxADB0. If the ADRIE bit is set, the module will generate an interrupt and stretch the clock after the 8th falling edge of SCL. This allows the client to determine the acknowledgement response to return to the host (see the figure below).