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Rev. 1.00, 05/04, page 264 of 544
12.6 Operation in Clocked Synchronous Mode
Figure 12.14 shows the general format for clocked synchronous communication. In clocked
synchronous mode, data is transmitted or received in synchronization with clock pulses. One
character in transfer data consists of 8-bit data. In data transmission, the SCI outputs data from one
falling edge of the synchronization clock to the next. In data reception, the SCI receives data in
synchronization with the rising edge of the synchronization clock. After 8-bit data is output, the
transmission line holds the MSB state. In clocked synchronous mode, no parity or multiprocessor
bit is added. 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 the next transmit data can be written during transmission or the
previous receive data can be read during reception, enabling continuous data transfer.
Don’t
care
Don’t
care
One unit of transfer data (character or frame)
Bit 0
Serial data
Synchronization
clock
Bit 1
Bit 3
Bit 4
Bit 5
LSB
MSB
Bit 2
Bit 6 Bit 7
*
*
Note: * High except in continuous transfer/reception
Figure 12.14 Data Format in Clocked Synchronous Communication (LSB-First)
12.6.1 Clock
Either an internal clock generated by the on-chip baud rate generator or an external
synchronization clock input at the SCK pin can be selected, according to the setting of the CKE1
and CKE0 bits in SCR. When the SCI is operated on an internal clock, the synchronization clock
is output from the SCK pin. Eight synchronization clock pulses are output in the transfer of one
character, and when no transfer is performed the clock is fixed high.