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(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.
The 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 an interrupt request flag (CSIIF3).
SCK3
SI3
SO3
CSIIF3
(3) Transfer start
A serial transfer starts when the following two conditions have been satisfied and transfer data has been set to
(or read from) serial I/O shift register 3 (SIO3).
• SIO3 operation control bit (CSIE3) = 1
• After an 8-bit serial transfer, the internal serial clock is either stopped or SCK3 is set to high level.
• Transmit or transmit/receive mode
When CSIE3 = 1 and MODE3 = 0, transfer starts when writing to SIO3.
• Receive-only mode
When CSIE3 = 1 and MODE3 = 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 sets an interrupt request flag
(CSIIF3).
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CHAPTER 15 SERIAL INTERFACE SIO3
Figure 15-3. 3-Wire Serial I/O Mode Timing
1
2
3
4
5
DI7
DI6
DI5
DI4
DI3
DO7 DO6 DO5 DO4 DO3 DO2 DO1
Transfer starts in synchronized with the falling edge of SCK3
Preliminary User's Manual U14581EJ3V0UM00
6
7
8
DI2
DI1
DI0
DO0
Transfer completion
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