CHAPTER 14 SERIAL INTERFACE CHANNEL 1
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User’s Manual U11302EJ4V0UM
14.4.2 3-wire serial I/O mode operation
The 3-wire serial I/O mode is used for connection of peripheral ICs and display controllers that incorporate
a clocked serial interface.
Communication is carried out using three lines: a serial clock (SCK1), serial output (SO1), and serial input
(SI1).
(1) Register setting
The 3-wire serial I/O mode is set by 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.
CSIM CSIM
Serial interface channel 1 clock selection
11
10
0
x
Clock externally input to SCK1 pin
Note 1
1
0
8-bit timer register 2 (TM2) output
1
1
Clock specified with bits 4 to 7 of timer clock select register 3 (TCL3)
ATE
Serial interface channel 1 operating mode selection
0
3-wire serial I/O mode
1
3-wire serial I/O mode with automatic transmit/receive function
DIR
Start bit
SI1 pin function
SO1 pin function
0
MSB
SI1/P20 (input)
SO1 (CMOS output)
1
LSB
CSIM
Shift register
Serial clock counter
SI1/P20
SO1/P21
SCK1/P22
CSIE1
PM20 P20 PM21 P21 PM22 P22
11
1 operation
operation control
pin function
pin function
pin function
Note 2 Note 2 Note 2 Note 2 Note 2 Note 2
Operation stop
Clear
P20
P21
P22
0
×
×
×
×
×
×
×
(CMOS I/O)
(CMOS I/O)
(CMOS I/O)
Operation enable Count operation
SI1
Note 3
SO1
SCK1
0
1
×
Note 3 Note 3
(input)
(CMOS output)
(input)
1
1
×
0
0
SCK1
1
0
1
(CMOS output)
Notes 1.
If 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.
2.
Can be used freely as a port pin.
3.
Can be used as P20 when used only for transmission (set bit 7 (RE) of ADTC to 0).
Remark
×
:
don’t care
PM
××
: Port mode register
P
××
:
Port output latch
CSIE1
DIR
ATE
0
0
0
CSIM
11
CSIM
10
<7>
6
<5>
4
3
2
1
0
CSIM1
Symbol
FF68H 00H R/W
Address After reset R/W