NEC Renesas V850/SC1 User Manual page 332

(b) Communication operations
In 3-wire serial I/O mode, data is transmitted and received in 8-bit units. Each bit of data is sent or received
in synchronization with the serial clock.
Serial I/O shift register n (SIOn) is shifted in synchronization with the falling edge of the serial clock.
Transmit data is held in the SOn latch and is output from the SOn pin. Data that is received via the SIn pin in
synchronization with the rising edge of the serial clock is latched to SIOn.
Completion of an 8-bit transfer automatically stops operation of SIOn and sets the interrupt request flag
(INTCSIn).
Serial clock
SI0
SO0
INTCSIn
(c) Transfer start
A serial transfer starts when the following two conditions have been satisfied and transfer data has been set
to serial I/O shift register n (SIOn).
• The SIOn operation control bit (CSIEn) = 1
• After an 8-bit serial transfer, the internal serial clock is either stopped or is set to high level.
The transfer data is set to SIOn as follows.
• Transmit/receive mode
When CSIEn = 1 and MODEn = 0, transfer starts when writing to SIOn.
• Receive-only mode
When CSIEn = 1 and MODEn = 1, transfer starts when reading from SIOn.
Caution After data has been written to SIOn, transfer will not start even if the CSIEn bit value is
set to 1.
Completion of an 8-bit transfer automatically stops the serial transfer operation and sets the interrupt request
flag (INTCSIn).
330
CHAPTER 11 SERIAL INTERFACE FUNCTION
Figure 11-4. Timing of 3-Wire Serial I/O Mode
1 2 3 4
DI7 DI6 DI5 DI4
DO7 DO6 DO5 DO4 DO3 DO2 DO1
Transfer starts in synchronization with the falling edge of the serial clock
User's Manual U15109EJ3V0UD
5 6 7 8
DI3 DI2 DI1 DI0
DO0
Transfer completion