MC68HC705MC4 Datasheet, PDF (77/99 Pages) Motorola, Inc – Microcontrollers

MC68HC705MC4 Specification Rev. 1.5
10.3 SCI DATA FORMAT
The SCI uses the standard non-return-to-zero mark/space data format illustrated in
Figure 10-1: SCI Data Format.
START
BIT
BIT 0
BIT 1
BIT 2
8-BIT DATA FORMAT
(BIT M IN SCCR1 CLEAR)
BIT 3 BIT 4 BIT 5 BIT 6
BIT 7
NEXT
STOP
BIT
START
BIT
START
BIT ^{BIT 0}
BIT 1
9-BIT DATA FORMAT
(BIT M IN SCCR1 SET)
BIT 2 BIT 3 BIT 4 BIT 5 BIT 6 BIT 7
Figure 10-1: SCI Data Format
BIT 8
NEXT
STOP ^START
BIT
BIT
10.4 SCI OPERATION
The SCI allows full-duplex, asynchronous, RS232 or RS422 serial communication
between 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. The following paragraphs describe the operation of the SCI transmitter and
receiver.
10.4.1 TRANSMITTER
Figure 10-2: SCI Transmitter shows the structure of the SCI transmitter.
10.4.1.1 Character Length
The transmitter can accommodate either 8-bit or 9-bit data. The state of the M bit in SCI
control register 1 (SCCR1) determines character length. When transmitting 9-bit data, bit
T8 in SCCR1 is the ninth bit (bit 8).
10.4.1.2 Character Transmission
During transmission, the transmit shift register shifts a character out to the PB4/TDO pin.
The SCI data register (SCDR) is the write-only buffer between the internal data bus and
the transmit shift register.
MOTOROLA
Page 68
Section 10: Serial Communications Interface