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16.3.4
Operation in Clocked Synchronous Mode
In clocked synchronous mode, data is transmitted or received in synchronization with clock
pulses, making it suitable for high-speed serial communication.
Inside the SCI, the transmitter and receiver are independent units, enabling full-duplex
communication by use of a common clock. Both the transmitter and the receiver also have a
double-buffered structure, so that data can be read or written during transmission or reception,
enabling continuous data transfer.
Figure 16-14 shows the general format for clocked synchronous serial communication.
*
Serial
clock
Serial
data
Don't care
Note: * High except in continuous transfer
Figure 16-14 Data Format in Synchronous Communication
In clocked synchronous serial communication, data on the transmission line is output from one
falling edge of the serial clock to the next. Data confirmation is guaranteed at the rising edge of
the serial clock.
In clocked serial communication, one character consists of data output starting with the LSB and
ending with the MSB. After the MSB is output, the transmission line holds the MSB state.
In clocked synchronous mode, the SCI receives data in synchronization with the rising edge of the
serial clock.
Data Transfer Format: A fixed 8-bit data format is used.
No parity or multiprocessor bits are added.
Clock: Either an internal clock generated by the on-chip baud rate generator or an external serial
clock input at the SCK pin can be selected, according to the setting of the C/A bit in SMR and the
CKE1 and CKE0 bits in SCR. For details of SCI clock source selection, see table 16-9.
When the SCI is operated on an internal clock, the serial clock is output from the SCK pin.
One unit of transfer data (character or frame)
LSB
Bit 0
Bit 1
Bit 2
Bit 3
Bit 4
Bit 5
*
MSB
Bit 6
Bit 7
Don't care
637
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