CHAPTER 16 ASYNCHRONOUS SERIAL INTERFACE/3-WIRE SERIAL I/O
User’s Manual U12697EJ3V0UM
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SIn
SCKn
1
2
3
4
5
6
7
8
DI7
DI6
DI5
DI4
DI3
DI2
DI1
DI0
SOn
DO7
DO6
DO5
DO4
DO3
DO2
DO1
DO0
SRIFn
Transfer start in synchronization with falling edge of SCKn
Transfer completion
(b) Communication operation
The 3-wire serial I/O mode performs data transfer in 8-byte units. Data is transmitted and received one byte
at a time in synchronization with the serial clock.
The shift operation of the serial I/O shift register n (SIOn) is performed in synchronization with the falling
edge of the serial clock (SCKn). Transmit data is held in the SOn latch, and is output from the SOn pin. Receive
data input to the SIn pin is latched to SIOn at the rising edge of the SCKn signal.
SIOn operation is automatically stopped when 8-bit transfer ends, and an interrupt request flag (SRIFn) is
set.
Remark
n = 1, 2
Figure 16-15. 3-Wire Serial I/O Mode Timing
Remark
n = 1, 2
(c) Transfer start
Serial transfer is started by setting transmit data (or reading) to serial I/O shift register n (SIOn) when the
following two conditions are satisfied.
• SIOn operation control bit (CSIEn) = 1
• Following 8-bit serial transfer, the internal serial clock is stopped, or SCKn is high level
• Transmit/receive mode
When CSIEn = 1 and MODEn = 0, and transfer is started with SIOn write
• Receive-only mode
When CSIEn = 1 and MODEn = 1, and transfer is started with SIOn read.
Caution
After data is written to SIOn, transfer will not start even if CSIEn is set to “1”.
Serial transfer automatically stops at the end of 8-bit transfer, and the interrupt request flag (SRIFn) is set.
Remark
n = 1, 2