NEC 78014Y Series User Manual page 302

(5) Pin configuration
The serial clock pin SCK0 and serial data bus pin SB0 (SB1) have the following configurations.
(a) SCK0 ............ Serial clock input/output pin
<1> Master .. CMOS and push-pull output
<2> Slave .... Schmitt input
(b) SB0 (SB1) .... Serial data input/output dual-function pin
Because the serial data bus line has an N-ch open-drain output, an external pull-up resistor is necessary.
Clock Output
(Clock Input)
N-ch Open-Drain
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Caution Because the N-ch open-drain output must be set to high-impedance at the time of data reception,
write FFH to the serial I/O shift register 0 (SIO0) in advance. However, when the wake-up function
specification bit (WUP) = 1, the N-ch open-drain output will always be set to high-impedance. Thus,
it is not necessary to write FFH to SIO0 before reception.
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CHAPTER 15 SERIAL INTERFACE CHANNEL 0 ( µ PD78014 Subseries)
Both master and slave devices have an N-ch open-drain output and a Schmitt input.
Figure 15-27. Pin Configuration
Master Device
SCK0
Serial Clock
SB0 (SB1)
Serial Data Bus
SO0
SI0
Slave Device
SCK0
V
DD
R
L
SB0 (SB1) N-ch Open-Drain
(Clock Output)
Clock Input
SO0
SI0