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CHAPTER 11 SERIAL INTERFACES SIO30 TO SIO32
User’s Manual U15104EJ2V0UD
11.4.2 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: serial clock (SCK3n), serial output (SO3n), and serial
input (SI3n) lines.
(1) Register setting
The 3-wire serial I/O mode is set using serial operating mode register 3n (CSIM3n).
These registers are set with a 1-bit or 8-bit memory manipulation instruction.
Reset input clears these registers to 00H.
CSIE3n
Enable/disable of SIO3n operation
Shift register operation
Serial counter
Port
0
Disables operation
Cleared
Port function
Note 1
1
Enables operation
Enables counter operation
Serial fu port function
Note 2
MODE3n
Transfer operation mode flag
Operating mode
Transfer start trigger
SO3n output
0
Transmit or transmit/receive mode
SIO3n write
Serial output
1
Receive-only mode
SIO3n read
Fixed to low level
Note 3
SCL3n1 SCL3n0
Clock selection
0
0
External clock input to SCK3n
0
1
f
X
/2
4
(281 kHz)
1
0
f
X
/2
5
(141 kHz)
1
1
f
X
/2
6
(70.3 kHz)
Notes 1. The SI3n, SO3n, and SCK3n pins can be used as port pins when CSIE3n = 0 (when SIO3n operation
is stopped).
2. When CSIE3n = 1 (when SIO3n operation is enabled), the SI3n pin can be used as a port pin if
only the transmission function is used, and the SO3n pin can be used as a port pin in the receive
mode.
3. The SO3n pin can be used as a port pin.
Remarks 1. f
X
: System clock oscillation frequency
2. ( ): f
X
= 4.5 MHz
Symbol
CSIM30
<7>
CSIE30
6
0
5
0
4
0
3
0
2
MODE30
1
SCL301
0
SCL300
R/W
R/W
After reset
00H
Address
FF6FH
R/W
FF6DH
00H
CSIM31
<7>
CSIE31
6
0
5
0
4
0
3
0
2
MODE31
1
SCL311
0
SCL310
R/W
FF6BH
00H
CSIM32
<7>
CSIE32
6
0
5
0
4
0
3
0
2
MODE32
1
SCL321
0
SCL320