With Quick Command enabled (QCEN in MCTRLA), the R/W# bit of the slave address denotes the command. This is a SMBus specific command where the R/W# bit may be used to simply turn a device function on or off, or enable/disable a low power standby mode. There is no data sent or received.
After the master receives an acknowledge from the slave, either RIF or WIF flag in MSTATUS will be set depending on polarity of R/W#. When either RIF or WIF flag is set after issuing a Quick Command, the TWI will accept a stop command through writing the CMD bits in MCTRLB.
Figure 1. Quick Command Frame Format
