H8SLASH3021 datasheet(402/712 Pages) RENESAS

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11. Serial Communication Interface

Rev.2.00 Mar. 22, 2007 Page 378 of 684

REJ09B0352-0200

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

Bit 0

Bit 1

Bit 2

Bit 3

Bit 4

Bit 5

Bit 6

Bit 7

LSB

MSB

Don't care

One unit (character or frame) of serial data

Transfer direction

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.

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