MC908AP8CFBE Datasheet, PDF (157/324 Pages) Freescale Semiconductor, Inc – Microcontrollers

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