3-Wire Serial I/O Mode Operation - NEC mPD780208 Subseries User Manual

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.
Symbol <7> 6 <5> 4
CSIM1
DIR ATE 0
CSIE1
CSIM CSIM
Serial interface channel 1 clock selection
11 10
0 x Clock externally input to SCK1 pin
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
0 MSB
1 LSB
CSIM
CSIE1 PM20 P20 PM21 P21 PM22 P22
11
Note 2 Note 2 Note 2 Note 2 Note 2 Note 2
× × ×
0
0
Note 3 Note 3
×
1 1
1
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 ×:
PM××: Port mode register
P××:
CHAPTER 14 SERIAL INTERFACE CHANNEL 1
3 2 1 0
Address
CSIM CSIM
0 0
FF68H
11 10
Note 1
Start bit
Shift register
1 operation
Operation stop
× × × ×
Operation enable Count operation
×
1
0 0
0 1
don't care
Port output latch
User's Manual U11302EJ4V0UM
After reset R/W
00H R/W
SI1 pin function
SI1/P20 (input)
Serial clock counter SI1/P20
operation control pin function
Clear P20
(CMOS I/O)
Note 3
SI1
(input)
SO1 pin function
SO1 (CMOS output)
SO1/P21 SCK1/P22
pin function pin function
P21 P22
(CMOS I/O) (CMOS I/O)
SO1 SCK1
(CMOS output) (input)
SCK1
(CMOS output)
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