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CHAPTER 15
SERIAL INTERFACE SIO3
User’s Manual U12790EJ2V0UD
15.4.2 3-wire serial I/O mode
The 3-wire serial I/O mode is useful for connecting a peripheral I/O or display controller equipped with a clocked
serial interface.
In this mode, communication is executed by using three lines: a serial clock (SCK3), serial output (SO3), and serial
input (SI3).
(1) Register setting
The 3-wire serial I/O mode is set by using serial operating mode register 3 (CSIM3).
(a) Serial operation mode register 3 (CSIM3)
This register is set by a 1-bit or 8-bit memory manipulation instruction.
The value of this register is initialized to 00H after reset.
CSIE3
Enable/disable of SIO3 operation
Shift register operation
Serial counter
Port
0
Operation disabled
Cleared
Port functionNote 1
1
Operation enabled
Counter operatio enabled
Serial function + port functionNote 2
MODE
Transfer operation mode flag
Operating mode
Transfer start trigger
SO3 output
0
Transmit or transmit/receive mode SIO3 write
Serial output
1
Receive-only mode
SIO3 read
Fixed to low levelNote 3
SCL31 SCL30
Selection of clock
0
External clock input to SCK3
01
fX/24 (394 kHz)
10
fX/25 (197 kHz)
11
fX/26 (98.4 kHz)
Notes 1. The SI3, SO3, and SCK3 pins can be used as port pins when CSIE3 = 0 (when SIO3 operation
is stopped).
2. When CSIE3 = 1 (when SIO3 operation is enabled), the SI3 pin can be used as a port pin if only
the transmission function is used, and the SO3 pin can be used as a port pin in the receive mode.
3. This pin can be used as a port pin (P71).
Remarks 1. fX: System clock oscillation frequency
2. ( ): fX = 6.3 MHz
Symbol
CSIM3
<7>
CSIE3
6
0
5
0
4
0
3
0
2
MODE
1
SCL31
0
SCL30
R/W
After reset
00H
Address
FF6FH