MC68HC08AS32A Datasheet, PDF (176/296 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
Serial Communications Interface (SCI)
INTERNAL BUS
CGMXCLK
÷4
PRE- BAUD
SCALER DIVIDER
÷ 16
SCP1
SCP0
SCR2
SCR1
SCR0
TXINV
SCI DATA REGISTER
11-BIT
TRANSMIT
SHIFT REGISTER
H876543210L
PTE0/TxD
M
PEN
PARITY
PTY
GENERATION
T8
TRANSMITTER CPU
INTERRUPT REQUEST
TRANSMITTER
CONTROL LOGIC
SCTE
SCTIE
TC
TCIE
SCTE
SCTIE
TC
TCIE
Figure 13-5. SCI Transmitter
SBK
LOOPS
ENSCI
TE
13.4.2.2 Character Transmission
During an SCI transmission, the transmit shift register shifts a character out to the
PTE0/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 by first reading SCI status register 1
(SCS1) and then writing to the SCDR.
4. Repeat step 3 for each subsequent transmission.
At the start of a transmission, transmitter control logic automatically loads the
transmit shift register with a preamble of logic 1s. After the preamble shifts out,
control logic transfers the SCDR data into the transmit shift register. A logic 0 start
Data Sheet
176
Serial Communications Interface (SCI)
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MC68HC08AS32A — Rev. 1
MOTOROLA