
Serial Communications Interface (SCI) Module
MC9S08RC/RD/RE/RG
144
MOTOROLA
11.1 Features
Features of SCI module include:
Full-duplex, standard non-return-to-zero (NRZ) format
Double-buffered transmitter and receiver with separate enables
Programmable baud rates (13-bit modulo divider)
Interrupt-driven or polled operation:
–
Transmit data register empty and transmission complete
–
Receive data register full
–
Receive overrun, parity error, framing error, and noise error
–
Idle receiver detect
Hardware parity generation and checking
Programmable 8-bit or 9-bit character length
Receiver wakeup by idle-line or address-mark
11.2 SCI System Description
The SCI allows full-duplex, asynchronous, NRZ serial communication among the MCU and remote
devices, including other MCUs. The SCI comprises a baud rate generator, transmitter, and receiver block.
The transmitter and receiver operate independently, although they use the same baud rate generator.
During normal operation, the MCU monitors the status of the SCI, writes the data to be transmitted, and
processes received data. The following describes each of the blocks of the SCI.
11.3 Baud Rate Generation
As shown in
Figure 11-2, the clock source for the SCI baud rate generator is the bus-rate clock.
Figure 11-2 SCI Baud Rate Generation
SBR12:SBR0
DIVIDE BY
Tx BAUD RATE
Rx SAMPLING CLOCK
(16
× BAUD RATE)
BAUD RATE GENERATOR
OFF IF [SBR12:SBR0] = 0
BUSCLK
BAUD RATE =
BUSCLK
[SBR12:SBR0]
× 16
16
MODULO DIVIDE BY
(1 THROUGH 8191)