Quick Command Mode

With Quick Command mode, the R/W bit from the address packet denotes the command. This mode is enabled by writing ‘1’ to the Quick Command Enable (QCEN) bit in the Host Control A (TWIn.MCTRLA) register. There are no data sent or received.

The Quick Command mode is SMBus specific, where the R/W bit can be used to turn a device function on/off or to enable/disable a low-power Standby mode. This mode can be enabled to auto-trigger operations and reduce software complexity.

After the host receives an ACK from the client, either the Read Interrupt Flag (RIF) or Write Interrupt Flag (WIF) will be set, depending on the value of the R/W bit. When either the RIF or WIF flag is set after issuing a Quick Command, the TWI will accept a Stop command by writing the Command (MCMD) bit field in the Host Control B (TWIn.MCTRLB) register.

The RIF and WIF flags, together with the value of the last Received Acknowledge (RXACK) flag, are all located in the Host Status (TWIn.MSTATUS) register.

Figure 1. Quick Command Frame Format