MC68HC908AT32 Datasheet, PDF (142/378 Pages) Freescale Semiconductor, Inc – Microcontrollers

Serial Communications Interface Module (SCI)
INTERNAL BUS
÷4
PRE- BAUD
SCALER DIVIDER
÷ 16
SCI DATA REGISTER
SCP1
SCP0
SCR1
SCR2
SCR0
11-BIT
TRANSMIT
SHIFT REGISTER
H876543210L
TxD
TXINV
M
PEN
PARITY
PTY
GENERATION
T8
TRANSMITTER
CONTROL LOGIC
SCTE
SCTE
SCTIE
TC
TCIE
SCTIE
TC
TCIE
Figure 16-4. SCI Transmitter
SBK
LOOPS
ENSCI
TE
16.4.2.1 Character Length
The transmitter can accommodate either 8-bit or 9-bit data. The state of the M bit in SCI control register 1
(SCC1) determines character length. When transmitting 9-bit data, bit T8 in SCI control register 3 (SCC3)
is the ninth bit (bit 8).
16.4.2.2 Character Transmission
During an SCI transmission, the transmit shift register shifts a character out to the TxD pin. The SCI data
register (SCDR) is the write-only buffer between the internal data bus and the transmit shift register. To
initiate an SCI transmission:
1. Enable the SCI by writing a logic 1 to the enable SCI bit (ENSCI) in SCI control register 1 (SCC1).
2. Enable the transmitter by writing a logic 1 to the transmitter enable bit (TE) in SCI control register
2 (SCC2).
3. Clear the SCI transmitter empty bit (SCTE) by first reading SCI status register 1 (SCS1) and then
writing to the SCDR.
4. Repeat step 3 for each subsequent transmission.
MC68HC908AT32 Data Sheet, Rev. 3.1
142
Freescale Semiconductor