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14.3
Operation
SCI3 can perform serial communication in two modes: asynchronous mode in which
synchronization is provided character by character, and synchronous mode in which
synchronization is provided by clock pulses. The serial mode register (SMR) is used to select
asynchronous or synchronous mode and the data transfer format, as shown in table 14.8.
The clock source for SCI3 is determined by bit COM in SMR and bits CKE1 and CKE0 in SCR3,
as shown in table 14.9.
14.3.1
Asynchronous Mode
• Data length is selectable: 7 or 8 bits.
• Parity and multiprocessor bits are selectable. So is the stop bit length (1 or 2 bits). These
selections determine the communication format and character length.
• In receiving, it is possible to detect framing errors, parity errors, overrun errors, and the break
state.
• An internal or external clock can be selected as the SCI clock source.
When an internal clock is selected, the SCI operates using the on-chip baud rate generator,
and can output a serial clock signal with a frequency matching the bit rate.
When an external clock is selected, the external clock input must have a frequency 16 times
the bit rate. (The on-chip baud rate generator is not used.)
14.3.2
Synchronous Mode
• The communication format has a fixed 8-bit data length.
• In receiving, it is possible to detect overrun errors.
• An internal or external clock can be selected as the SCI clock source.
When an internal clock is selected, the SCI operates using the on-chip baud rate generator,
and outputs a serial clock signal to external devices.
When an external clock is selected, the SCI operates on the input serial clock. The on-chip
baud rate generator is not used.
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