NEC 3. Be sure to set WUP to 0 when the 3-wire serial I/O mode is selected.

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CHAPTER 17 SERIAL INTERFACE CHANNEL 0 ( µ PD78058FY SUBSERIES)
17.4.2 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 clocked serial interface as is the case with the 75X/XL, 78K, and 17K Series.
Communication is carried out with three lines of serial clock (SCK0), serial output (SO0), and serial input (SI0).
(1) Register setting
The 3-wire serial I/O mode is set with the serial operating mode register 0 (CSIM0) and serial bus interface
control register (SBIC).
(a) Serial operating mode register 0 (CSIM0)
CSIM0 is set with a 1-bit or 8-bit memory manipulation instruction.
RESET input sets CSIM0 to 00H.
Notes 1. Bit 6 (COI) is a read-only bit.
2. Can be used as P25 (CMOS input/output) when used only for transmission.
3. Be sure to set WUP to 0 when the 3-wire serial I/O mode is selected.
Remark ×: don’t care
PMXX: Port Mode Register
PXX : Port Output Latch
65432107
Symbol
CSIM0 CSIE0 COI WUP
CSIM04 CSIM03 CSIM02 CSIM01 CSIM00
CSIM01
0
1
Serial Interface Channel 0 Clock Selection
Input Clock to SCK0 pin from off-chip
8-bit timer register 2 (TM2) output
0
2-wired serial I/O mode (see the section 17.4.3 2-wire serial I/O mode operation.)
R/W
1 Clock specified with bits 0 to 3 of timer clock select register 3 (TCL3)
CSIM
04
0
CSIM00
×
0
1
FF60H 00H R/W
Note 1
Address After Reset R/W
R/W
CSIM
03
CSIM
02 PM25 P25 PM26 P26 PM27 P27
Operation
Mode Start Bit
SIO/SB0/SDA0
/P25 Pin Function
SO0/SB1/SDA1
/P26 Pin Function
SCK0/SCL/P27
Pin Function
×
11
WUP
0
1
Wake-up Function Control
Note 3
Interrupt request signal generation with each serial transfer in any mode
Interrupt request signal generation when the address received after detecting start condition
(when CMDD=1) matches the slave address register (SVA) data in I
2
C bus mode
R/W
1
MSB
LSB
1×0001
Note 2
3-wire serial
l/O mode SI0 (Input) SO0 (CMOS output) SCK0 (CMOS input/output)
I
2
C bus mode (see the section 17.4.4 I
2
C bus mode operation.)
Note 2 Note 2
CSIE0
0
Serial Interface Channel 0 Operation Control
Operation stopped
Operation enabled
R/W
1
or