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CHAPTER 14 SERIAL INTERFACE SIO2
Preliminary User’s Manual U14581EJ3V0UM00
14.4.2 3-wire serial I/O mode
The 3-wire serial I/O mode is useful when connecting to devices such as peripheral I/Os and display controllers,
which incorporate a clocked serial interface.
This mode executes data transfer via three lines: a serial clock line (SCK2), a serial output line (SO2), and a serial
input line (SI2).
(1) Register settings
The 3-wire serial I/O mode is set with the serial operation mode register 2 (CSIM2).
CSIM2 is set with a 1-bit or 8-bit memory manipulation instruction.
RESET input clears CSIM2 to 00H.
Address: FF98H After Reset: 00H R/W
Symbol
7
6
5
4
3
2
1
0
CSIM2
CSIE2
0
0
CLPH
CLPO
MODE2
SCL21
SCL20
CSIE2
SIO2 Operation Enable/Disable Specification
Shift Register Operation
Serial Counter
Port
0
Operation disabled
Clear
Port function
1
Operation enabled
Counter operation enabled Serial fu port function
CLPH
SO2 Output Timing Sleleciton
0
Transfer starts at the first active edge of SCK2.
1
Transfer starts when SCK2 is written.
CLPO
Serial Clock Active Level Selection
0
SCK2 is high while serial transfer is stopped.
1
SCK2 is low while serial transfer is stopped.
MODE2
SIO2 Operation Mode Setting
Operation Mode
Transfer Start Trigger
SO2/P04 Pin
0
Transmit/receive mode
Writing to SIO2
SO output
1
Receive-only mode
Reading from SIO2
Port function
SCL21
SCL20
Serial Transfer Operation Clock Selection
Operation Clock (Transfer Frequency)
Master/Slave
0
0
External clock input to SCK2
Slave mode
0
1
f
X
/2
9
Master mode
1
0
f
X
/2
10
Master mode
1
1
f
X
/2
11
Master mode
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