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22.3
Operation
22.3.1
Overview
The SCI can carry out serial communication in two modes: asynchronous mode in which
synchronization is achieved character by character, and synchronous mode in which
synchronization is achieved with clock pulses.
Selection of asynchronous or synchronous mode and the transmission format is made using SMR1
as shown in table 22.8. The SCI clock is determined by a combination of the C/$ bit in SMR1
and the CKE1 and CKE0 bits in SCR1, as shown in table 22.9.
• Asynchronous Mode
Data length: Choice of 7 or 8 bits
Choice of parity addition, multiprocessor bit addition, and addition of 1 or 2 stop bits (the
combination of these parameters determines the transfer format and character length)
Detection of framing, parity, and overrun errors, and breaks, during reception
Choice of internal or external clock as SCI clock source
• When internal clock is selected:
The SCI operates on the baud rate generator clock and a clock with the same frequency
as the bit rate can be output
• When external clock is selected:
A clock with a frequency of 16 times the bit rate must be input (the built-in baud rate
generator is not used)
• Clock Synchronous Mode
Transfer format: Fixed 8-bit data
Detection of overrun errors during reception
Choice of internal or external clock as SCI clock source
• When internal clock is selected:
The SCI operates on the baud rate generator clock and a serial clock is output off-chip
• When external clock is selected:
The built-in baud rate generator is not used, and the SCI operates on the input serial
clock
Rev. 1.0, 02/00, page 422 of 1141
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