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CHAPTER 17 SERIAL INTERFACE CHANNEL 1
17.4.2 Operation in 3-wire serial I/O mode
This mode is useful for connecting peripheral I/Os and display controllers that have the conventional clocked serial
interface of the 75X/XL series, 78K series, and 17K series.
In this mode, communication is established by using three signal lines: serial clock (SCK1), serial output (SO1),
and serial input (SI1).
(1) Register setting
The 3-wire serial I/O mode is set by using the serial operation mode register 1 (CSIM1).
CSIM1 is set by a 1-bit or 8-bit memory manipulation instruction.
This register is set to 00H when the RESET signal is input.
Notes 1.
When external clock input is selected by setting CSIM11 to 0, set bit 1 (BUSY1) and bit 2 (STRB)
of the automatic data transmit/receive control register (ADTC) to 0, 0.
2.
These pins can be used freely as port pins.
3.
When data is only transmitted, this pin can be used as P20 (CMOS I/O) (set bit 7 (RE) of ADTC
to 0).
Remark
×
PM
××
: Port mode register
P
××
: Output latch of port
: Don’t care
1
×
Note 3 Note 3
×
×
×
×
6
5
4
3
2
1
0
7
Symbol
CSIM1 CSIE1
DIR
ATE
0
0
0
CSIM11 CSIM10
CSIM11
0
1
Selects clock of serial interface channel 1
Clock externally input to SCK1 pin
Note 1
Output of 8-bit timer register 2 (TM2)
1
Clock specified by bits 4-7 of timer clock select register 3 (TCL3)
CSIE1
CSIM10
×
0
1
FF68H 00H R/W
Address On reset R/W
CSIM
11
P20 PM21 P21 PM22
Shift register
1 operation
SO1/P21
pin function
SCK1/P22
pin function
×
×
0
0
Note 2 Note 2
Operation
disabled
ATE
0
Selects operation mode of serial interface channel 1
3-wire serial I/O mode
3-wire serial I/O mode with automatic transmit/receive function
1
DIR
0
First bit
MSB
LSB
1
SI1 pin function
SI1/P20
(input)
SO1 pin function
SO1
(CMOS output)
PM20
P22
Note 2 Note 2 Note 2
Note 2
×
0
1
0
1
0
1
1
×
Serial clock
count operation
control
SI1/P20
pin function
Cleared
P20
(CMOS I/O)
P21
(CMOS I/O)
P22
(CMOS I/O)
Operation
enabled
Count
operation
SI1
(input)
Note 3
SO1
(CMOS output)
SCK1
(input)
SCK1
(CMOS output)