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9 Serial Communications Interface (SCI)
The SCI, a universal asynchronous receiver transmitter (UART) serial communications interface, is one
of two independent serial I/O subsystems in the MC68HC11F1 and MC68HC11FC0. The SCI has a
standard non-return to zero (NRZ) format (one start bit, eight or nine data bits, and one stop bit) and
several selectable baud rates. The transmitter and receiver are independent but use the same data for-
mat and bit rate.
9.1 SCI Block Diagrams
TRANSMITTER
BAUD RATE
CLOCK
10 (11) - BIT Tx SHIFT REGISTER
H
(8) 7
SCCR1
SCI CONTROL 1
SCI Rx
SCI INTERRUPT
QUESTS
REQUEST
MOTOROLA
42
SCDR Tx BUFFER
6
5
4
3
2
1
0
L
TRANSMITTER
CONTROL LOGIC
SCSR1
SCI STATUS 1
TDRE
TIE
TC
TCIE
Figure 9 SCI Transmitter Block Diagram
(WRITE ONLY)
FORCE PIN
DIRECTION (OUT)
SCCR2
SCI CONTROL 2
DDD1
PIN BUFFER
PD1
AND CONTROL
TxD
INTERNAL
DATA BUS
MC68HC11F1/FC0
MC68HC11FTS/D
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