6 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 MC68HC11A8. It has a standard NRZ format (one start,
eight or nine data, and one stop bit) and several baud rates available. The SCI transmitter and receiver
are independent, but use the same data format and bit rate.
TRANSMITTER
BAUD RATE
CLOCK
(WRITE ONLY)
SCDR Tx BUFFER
DDD1
10 (11) - BIT Tx SHIFT REGISTER
PIN BUFFER
AND CONTROL
PD1
TxD
H
(8)
7
6
5
4
3
2
1
0
L
8
FORCE PIN
DIRECTION (OUT)
TRANSMITTER
CONTROL LOGIC
8
SCCR1 SCI CONTROL 1
SCSR INTERRUPT STATUS
8
TDRE
TIE
TC
TCIE
SCCR2 SCI CONTROL 2
SCI Rx
REQUESTS
SCI INTERRUPT
REQUEST
INTERNAL
DATA BUS
11 SCI TX BLOCK
Figure 6 SCI Transmitter Block Diagram
MC68HC11A8
MC68HC11A8TS/D
MOTOROLA
23
MOTOROLA [ MOTOROLA ]
