Datasheet

Section 15 Serial Communication Interface (SCI)
Rev. 6.00 Mar. 18, 2010 Page 602 of 982
REJ09B0054-0600
15.6 Operation in Clocked Synchronous Mode
Figure 15.17 shows the general format for clocked synchronous communication. In clocked
synchronous mode, data is transmitted or received synchronous with clock pulses. In clocked
synchronous serial communication, data on the transmission line is output from one falling edge of
the serial clock to the next. In clocked synchronous mode, the SCI receives data in synchronous
with the rising edge of the serial 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 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)
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 15.17 Data Format in Synchronous Communication (For LSB-First)
15.6.1 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 CKE0 and
CKE1 bits in SCR. When the SCI is operated on an internal clock, the serial clock is output from
the SCK pin. Eight serial clock pulses are output in the transfer of one character, and when no
transfer is performed the clock is fixed high.
15.6.2 SCI Initialization (Clocked Synchronous Mode)
Before transmitting and receiving data, the TE and RE bits in SCR should be cleared to 0, then the
SCI should be initialized as described in a sample flowchart in figure 15.18. When the operating
mode, or transfer format, is changed for example, the TE and RE bits must be cleared to 0 before
making the change using the following procedure. When the TE bit is cleared to 0, the TDRE flag
is set to 1. Note that clearing the RE bit to 0 does not change the contents of the RDRF, PER,
FER, and ORER flags, or the contents of RDR.