Datasheet

Section 18 Serial Communication Interface 4 (SCI4)
Rev. 2.00 Jul. 04, 2007 Page 422 of 692
REJ09B0309-0200
18.4 Operation
The SCI4 is a serial communication interface that transmits and receives data in synchronization
with a clock pulse and is suitable for high-speed serial communications. The data transfer format
is fixed to 8-bit data. The internal clock or external clock can be selected as a clock source. An
overrun error during reception can be detected. The transmit and receive units are configured with
double buffering mechanism. Since the mechanism enables to write data during transmission and
to read data during reception, data is consecutively transmitted and received.
18.4.1 Clock
The eight internal clocks or an external clock can be selected as a transfer clock. When the
external clock is selected, the SCK4 pin is a clock input pin. When the internal clock is selected,
the SCK4 pin is a synchronous clock output pin. The synchronous clock is output eight pulses for
1-character transmission or reception. While neither transmission nor reception is being
performed, the signal is fixed high.
When the internal clock or external clock is not selected according to the combination of the
CKS3 to CKS0 bits in SCSR4, the SCK4 pin functions as an I/O port.
18.4.2 Data Transfer Format
Figure 18.2 shows the SCI4 transfer format.
SCK4
SO4/SI4 Bit 0 Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Bit 6
Bit 7
Figure 18.2 Data Transfer Format
In clock synchronous communication, data on the communication line is output from the falling
edge to the next falling edge of the synchronous clock. The data is guaranteed to be settled at the
rising edge of the synchronous clock. One character starts with the LSB and ends with the MSB.
After transmitting the MSB, the communication line retains the MSB level.
The SCI4 latches data at the rising edge of the synchronous clock on reception. The data transfer
format is fixed to 8-bit data. While transmission is stopped, the output level on the SO4 pin can be
changed by the SOL setting in SCR4.