MC68HC812A4 Datasheet, PDF (258/342 Pages) Motorola, Inc – 16-bit device composed of standard on-chip peripheral modules connected by an intermodule bus. Modules include

Serial Communications Interface Module (SCI)
R8 — Received Bit 8
R8 is the ninth data bit received when the SCI is configured for 9-bit
data format (M = 1).
T8 — Transmitted Bit 8
T8 is the ninth data bit transmitted when the SCI is configured for 9-bit
data format (M = 1).
R7–R0 — Received Bits 7–0
T7–T0 — Transmitted Bits 7–0
NOTE:
If the value of T8 is the same as in the previous transmission, T8 does
not have to be rewritten. The same value is transmitted until T8 is
rewritten.
In 8-bit data format, only SCI data register low (SCDRL) needs to be
accessed.
When transmitting in 9-bit data format and using 8-bit write instructions,
write first to SCI data register high (SCDRH).
14.8 External Pin Descriptions
This section provides a description of TXD and RXD, the SCI’s two
external pins.
14.8.1 TXD Pin
TXD is the SCI transmitter pin. TXD is available for general-purpose I/O
when it is not configured for transmitter operation.
14.8.2 RXD Pin
RXD is the SCI receiver pin. RXD is available for general-purpose I/O
when it is not configured for receiver operation.
MC68HC812A4 — Rev. 3.0
258
Serial Communications Interface Module (SCI)
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