H8SLASH3028F datasheet(528/923 Pages) RENESAS

528 / 923 page

Rev. 2.00, 09/03, page 498 of 890

13.3.4

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 the 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 13.14 shows the general format in synchronous serial communication.

Don't care

One unit (character or frame) of transfer data

MSB

Bit 0

Bit 1

Bit 3

Bit 2

Bit 4

Bit 5

Bit 6

Bit 7

LSB

Don't care

Serial clock

Serial data

Note: * High except in continuous transmitting or receiving

Figure 13.14 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 transferred 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

An internal clock generated by the on-chip baud rate generator or an external clock input from the

SCK pin can be selected by means of the C/

A bit in SMR and the CKE1 and CKE0 bits in SCR.

See table 13.9 for details of SCI clock source selection.

When the SCI operates on an internal clock, it outputs the clock source 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. If receiving in single-character units is

required, an external clock should be selected.

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