Table of Contents
Advertisement
Functional description
22.5.6.3 Loop mode
When SCI_C1[LOOPS] is set, the SCI_C1[RSRC] bit in the same register chooses
between loop mode (SCI_C1[RSRC] = 0) or single-wire mode (SCI_C1[RSRC] = 1).
Loop mode is sometimes used to check software, independent of connections in the
external system, to help isolate system problems. In this 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.
22.5.6.4 Single-wire operation
When SCI_C1[LOOPS] is set, SCI_C1[RSRC] chooses between loop mode
(SCI_C1[RSRC] = 0) or single-wire mode (SCI_C1[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 SCI_C3[TXDIR] bit controls the direction of serial data on the
TxD pin. When SCI_C3[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 SCI_C3[TXDIR] is set, the TxD pin is an
output driven by the transmitter. In single-wire mode, the transmitter output is 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.
MC9S08SU16 Reference Manual, Rev. 5, 4/2017
420
NXP Semiconductors
Advertisement
Table of Contents
