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CHAPTER 14 SERIAL INTERFACE SIO3
User’s Manual U15798EJ2V0UD
(2) Communication operations
In the 3-wire serial I/O mode, data is transmitted and received in 8-bit units. Each bit of data is transmitted or
received in synchronization with the serial clock.
Serial I/O shift register 3 (SIO3) is shifted in synchronization with the falling edge of the serial clock. Transmission
data is held in the SO3 latch and is output from the SO3 pin. Data that is received via the SI3 pin in synchronization
with the rising edge of the serial clock is latched to SIO3.
Completion of an 8-bit transfer automatically stops operation of SIO3 and sets the interrupt request flag (CSIIF3).
Figure 14-3. Timing of 3-Wire Serial I/O Mode
(3) Transfer start
A serial transfer starts when the following two conditions have been satisfied and transfer data has been set (or
read) to serial I/O shift register 3 (SIO3).
• SIO3 operation control bit (CSIE3) = 1
• After an 8-bit serial transfer, either the internal serial clock is stopped or SCK3 is set to high level.
• Transmit/transmit and receive mode
When CSIE3 = 1 and MODE = 0, transfer starts when writing to SIO3.
• Receive-only mode
When CSIE3 = 1 and MODE = 1, transfer starts when reading from SIO3.
Caution After data has been written to SIO3, transfer will not start even if the CSIE3 bit value is set to
“1”.
Completion of an 8-bit transfer automatically stops the serial transfer operation and interrupt request flag (CSIIF3)
is set.
SI3
DI7
DI6
DI5
DI4
DI3
DI2
DI1
DI0
CSIIF3
SCK3
1
SO3
DO7
DO6
DO5
DO4
DO3
DO2
DO1
DO0
2
3
4
5
6
7
8
Transfer completion
Transfer starts in synchronization with the SCK3 falling edge