2 3-wire serial i/o mode operation – NEC uPD78P078 User Manual
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CHAPTER 19 SERIAL INTERFACE CHANNEL 1
19.4.2 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.
6
<5>
4
3
2
1
0
<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
x
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
SI1 Pin Function
SI1/P20
(Input)
SO1 Pin Function
SO1
(CMOS output)
Operation
enable
SCK1
(Input)
CSIE
1
0
CSIM
11
P20 PM21 P21 PM22
Shift Register 1
Operation
Serial Clock Counter
Operation Control
SI1/P20 Pin
Function
SCK1/P22
Pin Function
x
1
0
1
0
x
0
0
1
x
1
Note 1 Note 1 Note 1 Note 1
Count
operation
SI1
Note 2
(Input)
x
x
x
x
x
Operation
stop
Clear
P20 (CMOS
input/output)
P22 (CMOS
input/output)
x
PM20
SO1/P21 Pin
Function
SO1 (CMOS
output)
P21 (CMOS
input/output)
SCK1
(CMOS
output)
1
Note 1
Note 1
Note 2
Note 2
P22
Notes 1. 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.
2. Can be used freely as port function.
3. Can be used as P20 (CMOS input/output) when only transmitter is used (set bit 7 (RE) of ADTC
to 0).
Remark
x
: Don’t care
PMxx : Port mode register
Pxx
: Port output latch