Freescale Semiconductor, Inc.
Serial Communications Interface (SCI)
SCI Operation
Addr.
Register Name
Bit 7
6
5
SCP1
0
4
SCP0
0
3
2
SCR2
U
1
SCR1
U
Bit 0
SCR0
U
Read:
Baud Rate Register
$000D
(Baud) Write:
See page 136.
Reset:
Read:
U
R8
U
U
T8
U
WAKE
U
SCI Control Register 1
M
$000E
$000F
$0010
$0011
(SCCR1) Write:
See page 130.
Reset:
Read:
U
U
SCI Control Register 2
TIE
TCIE
RIE
ILIE
TE
RE
RWU
SBK
0
(SCCR2) Write:
See page 131.
Reset:
0
0
0
0
0
0
0
Read: TDRE
TC
RDRF
IDLE
OR
NF
FE
SCI Status Register
(SCSR) Write:
See page 133.
Reset:
Read:
1
1
0
0
0
0
0
U
SCI Data Register
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
(SCDR) Write:
See page 129.
Reset:
Unaffected by reset
U = Unaffected
= Unimplemented
Figure 10-3. SCI Transmitter I/O Register Summary
Writing a logic 1 to the TE bit in SCI control register 2 (SCCR2) and
then writing data to the SCDR begins the 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, the control logic transfers the SCDR data into
the shift register. A logic 0 start bit automatically goes into the least
significant bit (LSB) position of the shift register, and a logic 1 stop
bit goes into the most significant bit (MSB) position.
When the data in the SCDR transfers to the transmit shift register,
the transmit data register empty (TDRE) flag in the SCI status
register (SCSR) becomes set. The TDRE flag indicates that the
SCDR can accept new data from the internal data bus.
When the shift register is not transmitting a character, the
PD1/TDO pin goes to the idle condition, logic 1. If software clears
the TE bit during the idle condition, and while TDRE is set, the
transmitter relinquishes control of the PD1/TDO pin.
MC68HC705C8A — Rev. 3
MOTOROLA
Technical Data
Serial Communications Interface (SCI)
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