MC9S08RC8 Datasheet, PDF (162/234 Pages) Freescale Semiconductor, Inc – Microcontrollers

Serial Communications Interface (S08SCIV1)
internally connected to the receiver input and the RxD1 pin is not used by the SCI, so it reverts to a
general-purpose port I/O pin.
12.3.5.4 Single-Wire Operation
When LOOPS = 1, the RSRC bit in the same register chooses between loop mode (RSRC = 0) or
single-wire mode (RSRC = 1). Single-wire mode is used to implement a half-duplex serial connection.
The receiver is internally connected to the transmitter output and to the TxD1 pin. The RxD1 pin is not
used and reverts to a general-purpose port I/O pin.
In single-wire mode, the TXDIR bit in SCI1C3 controls the direction of serial data on the TxD1 pin. When
TXDIR = 0, the TxD1 pin is an input to the SCI receiver and the transmitter is temporarily disconnected
from the TxD1 pin so an external device can send serial data to the receiver. When TXDIR = 1, the TxD1
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.
MC9S08RC/RD/RE/RG Data Sheet, Rev. 1.11
162
Freescale Semiconductor