Datasheet

For coherent writes to the transmit data buffer, write to the SCI_C3[T8] bit before writing
to SCI_D.
If the bit value to be transmitted as the ninth bit of a new character is the same as for the
previous character, it is not necessary to write to SCI_C3[T8] again. When data is
transferred from the transmit data buffer to the transmit shifter, the value in SCI_C3[T8]
is copied at the same time data is transferred from SCI_D to the shifter.
The 9-bit data mode is typically used with parity to allow eight bits of data plus the parity
in the ninth bit, or it is used with address-mark wakeup so the ninth data bit can serve as
the wakeup bit. In custom protocols, the ninth bit can also serve as a software-controlled
marker.
15.3.5.2 Stop mode operation
During all stop modes, clocks to the SCI module are halted.
No SCI module registers are affected in stop3 mode.
Because the clocks are halted, the SCI module resumes operation upon exit from stop,
only in stop3 mode. Software must ensure stop mode is not entered while there is a
character being transmitted out of or received into the SCI module.
15.3.5.3 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 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.
15.3.5.4 Single-wire operation
When SCI_C1[LOOPS] is set, the RSRC bit in the same register 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.
Chapter 15 Serial communications interface (SCI)
MC9S08PA60 Reference Manual, Rev. 1, 9/2012
Freescale Semiconductor, Inc. 423