MC68HC05B6_13 Datasheet, PDF (73/302 Pages) Freescale Semiconductor, Inc – Microcontrollers

6
SERIAL COMMUNICATIONS INTERFACE
A full-duplex asynchronous serial communications interface (SCI) is provided with a standard
non-return-to-zero (NRZ) format and a variety of baud rates. The SCI transmitter and receiver are
functionally independent and have their own baud rate generator; however they share a common
baud rate prescaler and data format.
The serial data format is standard mark/space (NRZ) and provides one start bit, eight or nine data
6
bits, and one stop bit.
The SCLK pin is the output of the transmitter clock. It outputs the transmitter data clock for
synchronous transmission (no clocks on start bit and stop bit, and a software option to send clock
on last data bit). This allows control of peripherals containing shift registers (e.g. LCD drivers).
Phase and polarity of these clocks are software programmable.
Any SCI bidirectional communication requires a two-wire system: receive data in (RDI) and
transmit data out (TDO).
‘Baud’ and ‘bit rate’ are used synonymously in the following description.
6.1
SCI two-wire system features
• Standard NRZ (mark/space) format
• Advanced error detection method with noise detection for noise duration of up to 1/16th bit time
• Full-duplex operation (simultaneous transmit and receive)
• 32 software selectable baud rates
• Different baud rates for transmit and receive; for each transmit baud rate, 8 possible receive
baud rates
• Software selectable word length (eight or nine bits)
• Separate transmitter and receiver enable bits
• Capable of being interrupt driven
• Transmitter clocks available without altering the regular transmitter or receiver functions
• Four separate enable bits for interrupt control
MC68HC05B6
Rev. 4.1
SERIAL COMMUNICATIONS INTERFACE
Freescale
6-1