Functional Description
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).
INTERNAL BUS
SCI DATA
REGISTER
SCI DATA
REGISTER
RECEIVE
SHIFT REGISTER
TRANSMIT
SHIFT REGISTER
RxD
TxD
TXINV
SCTIE
TCIE
SCRIE
ILIE
R8
T8
DMARE
DMATE
TE
SCTE
TC
RE
RWU
SBK
SCRF
IDLE
OR
NF
FE
PE
ORIE
NEIE
FEIE
PEIE
LOOPS
ENSCI
LOOPS
RECEIVE
CONTROL
FLAG
CONTROL
TRANSMIT
CONTROL
WAKEUP
CONTROL
SCIBDSRC
FROM
CONFIG
M
BKF
RPF
ENSCI
WAKE
ILTY
PEN
PTY
SL
A
PRE-
SCALER
BAUD
DIVIDER
CGMXCLK
BUS CLOCK
÷ 4
X
B
SL = 0 => X = A
SL = 1 => X = B
DATA SELECTION
CONTROL
÷ 16
CGMXCLK is from CGM module
Figure 11-2. SCI Module Block Diagram
MC68HC908AP Family Data Sheet, Rev. 4
Freescale Semiconductor
157
FREESCALE [ Freescale ]
