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11.3.4 Synchronous Operation
In synchronous mode, the SCI transmits and receives data in synchronization with clock pulses.
This mode is suitable for high-speed serial communication.
The SCI transmitter and receiver share the same clock but are otherwise independent, so full
duplex communication is possible. The transmitter and receiver are also double buffered, so
continuous transmitting or receiving is possible by reading or writing data while transmitting or
receiving is in progress.
Figure 11-14 shows the general format in synchronous serial communication.
*
Serial clock
Serial data
Don't care
Note: * High except in continuous transmitting or receiving
Figure 11-14 Data Format in Synchronous Communication
In synchronous serial communication, each data bit is placed on the communication line from one
falling edge of the serial clock to the next. Data is guaranteed valid at the rise of the serial clock.
In each character, the serial data bits are transmitted in order from LSB (first) to MSB (last). After
output of the MSB, the communication line remains in the state of the MSB. In synchronous mode
the SCI receives data by synchronizing with the rise of the serial clock.
Communication Format: The data length is fixed at 8 bits. No parity bit or multiprocessor bit
can be added.
Clock: Either an internal clock generated by the built-in 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 on SCI clock source selection, see table 11-9. When the
SCI operates on an internal clock, it outputs the clock signal at the SCK pin. Eight clock pulses are
output per transmitted or received character. When the SCI is not transmitting or receiving, the
clock signal remains in the high state.
368
Transfer direction
One unit (character or frame) of serial data
LSB
Bit 0
Bit 1
Bit 2
Bit 3
Bit 4
Bit 5
*
MSB
Bit 6
Bit 7
Don't care
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