Datasheet

Functional Description
MC68HC908AP Family Data Sheet, Rev. 4
Freescale Semiconductor 157
11.4 Functional Description
Figure 11-2 shows the structure of the SCI module. The SCI allows full-duplex, asynchronous, NRZ serial
communication among the MCU and remote devices, including other MCUs. The transmitter and receiver
of the SCI operate independently, although they use the same baud rate generator. During normal
operation, the CPU monitors the status of the SCI, writes the data to be transmitted, and processes
received data.
The baud rate clock source for the SCI can be selected via the configuration bit, SCIBDSRC, of the
CONFIG2 register ($001D).
Figure 11-2. SCI Module Block Diagram
SCTE
TC
SCRF
IDLE
OR
NF
FE
PE
SCTIE
TCIE
SCRIE
ILIE
TE
RE
RWU
SBK
R8
T8
DMATE
ORIE
FEIE
PEIE
BKF
RPF
SCI DATA
RECEIVE
SHIFT REGISTER
SCI DATA
REGISTER
TRANSMIT
SHIFT REGISTER
NEIE
M
WAKE
ILTY
FLAG
CONTROL
TRANSMIT
CONTROL
RECEIVE
CONTROL
DATA SELECTION
CONTROL
WAKEUP
PTY
PEN
REGISTER
DMA
INTERRUPT
CONTROL
TRANSMITTER
INTERRUPT
CONTROL
RECEIVER
INTERRUPT
CONTROL
ERROR
INTERRUPT
CONTROL
CONTROL
DMARE
ENSCI
LOOPS
ENSCI
INTERNAL BUS
TXINV
LOOPS
÷ 4
÷ 16
PRE-
SCALER
BAUD
DIVIDER
CGMXCLK
BUS CLOCK
A
B
SL
X
SCIBDSRC
FROM
SL = 0 => X = A
SL = 1 => X = B
CONFIG
RxD
TxD
CGMXCLK is from CGM module