CHAPTER 10 SERIAL INTERFACE FUNCTION
User’s Manual U13850EJ4V0UM
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(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.
Transmission 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).
Figure 10-6. Timing of 3-Wire Serial I/O Mode
SI0
DI7
DI6
DI5
DI4
DI3
DI2
DI1
DI0
INTCSIn
Serial clock
1
SO0
DO7
DO6
DO5
DO4
DO3
DO2
DO1
DO0
2
3
4
5
6
7
8
Transfer completion
Transfer starts in synchronization with the serial clock’s falling edge
(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 to SIOn is set 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).