SLUSDQ4 April 2019 BQ79606A-Q1
Use the Communication Clear command to clear the receiver and instruct it to look for a new start of frame. The next byte following the Break is considered a "start of frame" byte. The receiver continuously monitors the RX line for break condition. A communication clear is detected when the RX line is held low for a least a min value of tUART(BRK) bit periods. Ensure that the break does not exceed the max value of tUART(BRK) bit periods, as this may result in recognition of a SLEEPtoACTIVE and/or communication reset (if RX held low long enough to satisfy tUART(RST). When detected, a communication clear sets the COMM_UART_FAULT[COMMCLR_DET] flag. The host must wait at least tUART(RXMIN) after the communication clear to start sending the frame. It should be noted that in addition to the COMM_UART_FAULT[COMMCLR_DET] flag, the COMM_UART_FAULT[STOP] flag is also set because the communication clear timing violates the typical byte timing and the STOP bit is seen as '0'.
While using the daisy-chain configuration (CONFIG[MULTIDROP_EN] = 0), if a communication clear is received (Base or Bridge) while waiting to respond to a read command, the device response is discarded and the COMM_UART_TR_FAULT[WAIT] or COMM_UART_TR_FAULT[SOF] bit is set (depending on the timing of receiving the communication clear). The stack devices do NOT see the communication clear and continue to send their responses which are forwarded to the host. In the stack configuration, the host should avoid this condition by waiting until all responses are received from the stack before sending a communication clear. Failure to do so results in the host receiving unexpected response frames.
When using the multi-drop configuration (CONFIG[MULTIDROP_EN] = 1), a communication clear must be used before every frame to ensure consistent communication. If a communication clear is received during a response, or while waiting to respond, the responses are immediately discarded (if waiting to transmit) or stopped (if currently transmitting) and the COMM_UART_TR_FAULT[WAIT] bit is set.
Note that for a device in sleep mode, sleep to active causes only communication clear detect COMM_UART_FAULT[COMMCLR_DET], but no COMM_UART_FAULT[STOP]. For a device in active mode, sleep to active causes both communication clear detect and STOP