14.4.6.3 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.
14.4.6.4 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.
Chapter 14 Serial communications interface (SCI)
MC9S08PA4 Reference Manual, Rev. 5, 08/2017
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Summary of Contents for MC9S08PA4
Page 1: ...MC9S08PA4 Reference Manual Supports MC9S08PA4 Document Number MC9S08PA4RM Rev 5 08 2017 ...
Page 2: ...MC9S08PA4 Reference Manual Rev 5 08 2017 2 NXP Semiconductors ...
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Page 28: ...System clock distribution MC9S08PA4 Reference Manual Rev 5 08 2017 28 NXP Semiconductors ...
Page 150: ...Port data registers MC9S08PA4 Reference Manual Rev 5 08 2017 150 NXP Semiconductors ...
Page 196: ...Human machine interfaces HMI MC9S08PA4 Reference Manual Rev 5 08 2017 196 NXP Semiconductors ...
Page 224: ...Instruction Set Summary MC9S08PA4 Reference Manual Rev 5 08 2017 224 NXP Semiconductors ...
Page 232: ...Functional Description MC9S08PA4 Reference Manual Rev 5 08 2017 232 NXP Semiconductors ...
Page 258: ...FTM Interrupts MC9S08PA4 Reference Manual Rev 5 08 2017 258 NXP Semiconductors ...
Page 294: ...Functional description MC9S08PA4 Reference Manual Rev 5 08 2017 294 NXP Semiconductors ...
Page 398: ...Resets MC9S08PA4 Reference Manual Rev 5 08 2017 398 NXP Semiconductors ...
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