HD643303x Hitachi, HD643303x Datasheet - Page 371

• Manufacturer Part Number: HD643303x
• Description: Hitachi Microcomputer
• Manufacturer: Hitachi

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.
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: An internal clock generated by the on-chip baud rate generator or an external clock input
from the SCK pin can be selected by clearing or setting the CKE1 bit in SCR. 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. When the SCI is only receiving, it receives in
units of two characters, so it outputs 16 clock pulses. To receive in units of one character, an
external clock source must be selected.
Serial data
Serial clock
Note:
*
High except in continuous transmitting or receiving
Don’t care
Figure 11-14 Data Format in Synchronous Communication
*
Bit 0
LSB
Transfer direction
Bit 1
One unit (character or frame) of serial data
Bit 2
356
Bit 3
Bit 4
Bit 5
Bit 6
MSB
Bit 7
Don’t care
*