Datasheet

Section 15 Serial Communication Interface 3 (SCI3)
Rev. 2.00 Sep. 23, 2005 Page 264 of 444
REJ09B0068-0200
15.5 Operation in Clocked Synchronous Mode
Figure 15.9 shows the general format for clocked synchronous communication. In clocked
synchronous mode, data is transmitted or received synchronous with clock pulses. A single
character in the transmit data consists of the 8-bit data starting from the LSB. In clocked
synchronous serial communication, data on the transmission line is output from one falling edge of
the synchronization clock to the next. In clocked synchronous mode, the SCI3 receives data in
synchronous 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 SCI3, the transmitter and receiver are independent units, enabling full-
duplex communication through the use of a common clock. Both the transmitter and the receiver
also have a double-buffered structure, so data can be read or written during transmission or
reception, enabling continuous data transfer.
Don't care Don't care
One unit of transfer data (character or frame)
8-bit
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
Figure 15.9 Data Format in Clocked Synchronous Communication
15.5.1 Clock
Either an internal clock generated by the on-chip baud rate generator or an external
synchronization clock input at the SCK3 pin can be selected, according to the setting of the COM
bit in SMR and the CKE0 and CKE1 bits in SCR3. When the SCI3 is operated on an internal
clock, the synchronization clock is output from the SCK3 pin. Eight synchronization clock pulses
are output in the transfer of one character, and when no transfer is performed the clock is fixed
high.
15.5.2 SCI3 Initialization
Before transmitting and receiving data, the SCI3 should be initialized as described in a sample
flowchart in figure 15.4.