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CHAPTER 18 SERIAL INTERFACE CHANNEL 1
18.4.2 3-wire serial I/O mode operation
The 3-wire serial I/O mode is valid for connection of peripheral I/O units and display controllers which incorporate
a conventional synchronous serial interface such as the 75X/XL, 78K and 17K series.
Communication is carried out with three lines of serial clock (SCK1), serial output (SO1) and serial input (SI1).
(1) Register setting
The 3-wire serial I/O mode is set with the serial operating mode register 1 (CSIM1).
CSIM1 is set with a 1-bit or 8-bit memory manipulation instruction.
RESET input sets CSIM1 to 00H.
Note If the external clock input has been selected with CSIM11 set to 0, set bit 1 (BUSY1) and bit 2 (STRB)
of the automatic data transmit/receive control register (ADTC) to 0, 0.
Remark ×: Don't care
Notes 1. Can be used freely as port function.
2. Can be used as P20 (CMOS input/output) when only transmitter is used (clear bit 7 (RE) of ADTC
to 0).
Remark × : Don't care
PM×× : Port mode register
P×× : Port output latch
6<5>43210<7>
Symbol
CSIM1 CSIE1 DIR ATE 0 0 0
CSIM11 CSIM10
CSIM11
0
1
Serial Interface Channel 1 Clock Selection
Clock externally input to SCK1 pin
Note
8-bit timer register 2 (TM2) output
1 Clock specified with bits 4 to 7 of timer clock select register 3 (TCL3)
CSIM10
×
0
1
FF68H 00H R/W
Address After Reset R/W
ATE
0
1
Serial Interface Channel 1 Operating Mode Selection
3-wire serial I/O mode
3-wire serial I/O mode with automatic transmit/receive function
DIR
0
1
Start Bit
MSB
LSB
SO1 Pin Function
SI1/P20
(Input)
SO1 Pin Function
SO1
(CMOS output)
Operation
enable
SCK1
(Input)
CSIE1
0
CSIM11
P20 PM21 P21 PM22
Note 2
Shift Register 1
Operation
Serial Clock Counter
Operation Control
SI1/P20 Pin
Function
SCK1/P22
Pin Function
×
1
0
1
0
× 00
1×
1
Note 1 Note 1
Note 1 Note 1
Count
operation
SI1
(Input)
×××××
Operation
stop
Clear P20 (CMOS
input/output)
P22 (CMOS
input/output)
×
PM20
SO1/P21 Pin
Function
SO1 (CMOS
output)
P21 (CMOS
input/output)
SCK1
(CMOS
output)
1
Note 1
Note 1
Note 2Note 2
P22