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CHAPTER 14
SERIAL INTERFACE SIO1
User’s Manual U12790EJ2V0UD
14.4.2 3-wire serial I/O mode operation
The 3-wire serial I/O mode is effective for connection of peripheral I/O units and display controllers that incorporate
a conventional synchronous serial interface such as the 75XL, 78K and 17K Series.
Communication is carried out with three lines, one each for the serial clock (SCK1), serial output (SO1), and serial
input (SI1).
(1) Register setting
The 3-wire serial I/O mode is set using serial operating mode register 1 (CSIM1), port mode register 2 (PM2),
and port 2 (P2).
(a) Serial operating mode register 1 (CSIM1)
CSIM1 is set by a 1-bit or 8-bit memory manipulation instruction.
Reset input sets CSIM1 to 00H.
CSIE1
Enable/disable of operation of serial interface SIO1
Shift register operation
Serial counter
PortNote 1
0
Operation stopped
Cleared
Port function
1
Operation enabled
Count operation enabled
Serial function + port function
DIR1
Start bit
0
MSB
1
LSB
ATE
Selection of operating mode of serial interface SIO1
0
3-wire serial I/O mode
1
3-wire serial I/O mode with automatic transmit/receive function
LSCK1
Chip enable control of SCK1 pin
0
SCK1 is used as port (P22) when CSIE1 = 0.
SCK1 is used for clock output when CSIE1 = 1.
1
SCK1 is fixed to high level when CSIE1 = 0.
SCK1 is used for clock output when CSIE1 = 1.
SCL11 SCL10
Selection of serial clock of serial interface SIO1
0
External clock input to SCK1 pinNote 2
01
fX/24 (394 kHz)
10
fX/25 (197 kHz)
11
fX/26 (98.4 kHz)
<7>
CSIE1
6
DIR1
<5>
ATE
4
LSCK1
3
0
2
0
1
SCL11
0
SCL10
Symbol
CSIM1
R/W
After reset
00H
Address
FF68H