H8SSLASH2218 datasheet(467/750 Pages) RENESAS

467 / 750 page

Section 12 Serial Communication Interface

Rev.6.00 Jun. 03, 2008 Page 419 of 698

REJ09B0074-0600

12.6

Operation in Clocked Synchronous Mode

Figure 12.17 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 from or written during transmission or reception, enabling

continuous data transfer.

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 12.17 Data Format in Synchronous Communication (For 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 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.

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