CM68HC05C4ACFB Motorola / Freescale Semiconductor, CM68HC05C4ACFB Datasheet - Page 65

• Manufacturer Part Number: CM68HC05C4ACFB
• Description: Microcontroller
• Manufacturer: Motorola / Freescale Semiconductor

9.5 SCI Operation
9.5.1 Transmitter
9.5.1.1 Character Length
9.5.1.2 Character Transmission
MC68HC05C4A
MOTOROLA
—
Rev. 4.0
The SCI allows full-duplex, asynchronous, RS232 or RS422 serial
communication between the MCU and remote devices, including other
MCUs. The SCI’s transmitter and receiver operate independently,
although they use the same baud-rate generator. The following
paragraphs describe the operation of the SCI transmitter and receiver.
Figure 9-2
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).
During transmission, the transmit shift register shifts a character out to
the PD1/TDO pin. The SCI data register (SCDR) is the write-only buffer
between the internal data bus and the transmit shift register.
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 position of the
shift register, and a logic 1 stop bit goes into the most significant bit
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.
Serial Communications Interface (SCI)
shows the structure of the SCI transmitter.
Serial Communications Interface (SCI)
General Release Specification
SCI Operation
65