
178
CHAPTER 8 SERIAL INTERFACE FUNCTION
8.3.7 Transmission/reception in 3-wire serial I/O mode
Transmission and reception can be executed simultaneously if both transmission and reception are enabled by
the clocked serial interface mode register n (CSIMn) (n = 0 to 3).
(1) Starting transmission/reception
Transmission and reception can be performed simultaneously (transmission/reception operation) when both
the CTXEn and CRXEn bits of the clocked serial interface mode registers n (CSIMn) are set to 1.
Transmission/reception can be started by writing the transmit data to the shift register n (SIOn) when both
the CTXEn and CRXEn bits of the CSIMn registers are “1” (transmission/reception enabled).
If CRXEn has already been set to 1, writing “1” to this bit does not initiate transmit/receive operation.
(2) Transmitting data in synchronization with serial clock
(a) When internal clock is selected as serial clock
When transmission/reception is started, the serial clock is output from the SCKn pin, and at the same
time, data is sequentially set to the SOn pin from SIOn register in synchronization with the falling edge
of the serial clock. Simultaneously, the data of the SIn pin is sequentially loaded to SIOn register in
synchronization with the rising edge of the serial clock.
(b) When external clock is selected as serial clock
When transmission/reception is started, the data is sequentially output from SIOn register to the SOn pin
in synchronization with the falling edge of the serial clock input to the SCKn pin immediately after
transmission/reception has been started. The data of the SIn pin is sequentially loaded to SIOn register
in synchronization with the rising edge of the serial clock. The shift operation is not performed even if the
serial clock is input to the SCKn pin when transmission/reception is not enabled, and the output level of
the SOn pin does not change.
Figure 8-9. Timing of 3-Wire Serial I/O Mode (Transmission/Reception)
Remark
n = 0 to 3
DI7 DI6 DI5 DI4 DI3 DI2 DI1 DI0
DO7 DO6 DO5 DO4 DO3 DO2 DO1 DO0
1
2
3
4
5
6
7
8
SCKn
SIn
SOn
INTCSIn
Transfer starts in synchronization with falling edge of SCKn
Execution of SIOn register write instruction
Serial transmission/
reception completion
interrupt occurs