internally connected to the receiver input and the RxD pin is not used by the SCI, so it reverts to a general-purpose port I/O pin.

15.3.5.4Single-Wire Operation

When LOOPS is set, the RSRC bit in the same register chooses between loop mode (RSRC = 0) or single-wire mode (RSRC = 1). Single-wire mode implements a half-duplex serial connection. The receiver is internally connected to the transmitter output and to the TxD pin. The RxD pin is not used and reverts to a general-purpose port I/O pin.

In single-wire mode, the TXDIR bit in SCIxC3 controls the direction of serial data on the TxD pin. When TXDIR is cleared, the TxD pin is an input to the SCI receiver and the transmitter is temporarily disconnected from the TxD pin so an external device can send serial data to the receiver. When TXDIR is set, the TxD pin is an output driven by the transmitter. In single-wire mode, the internal loop back connection from the transmitter to the receiver causes the receiver to receive characters that are sent out by the transmitter.

MCF51QE128 MCU Series Reference Manual, Rev. 3

Freescale Semiconductor

311

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Freescale Semiconductor MCF51QE128RM manual Single-Wire Operation, Freescale Semiconductor 311