NEC PD750008 - Manual (Page 187)

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CHAPTER 5 PERIPHERAL HARDWARE FUNCTIONS
(6) Pin configuration
The configurations of serial clock pin SCK and serial data bus pin (SB0 or SB1) are as follows:
(a) SCK: Pin for serial clock I/O
<1> Master : CMOS, push-pull output
<2> Slave : Schmitt input
(b) SB0, SB1: Pin for serial data I/O
Output to SB0 or SB1 is an N-ch open-drain output and input is Schmitt input for both
the master and a slave.
The serial data bus line must be externally pulled up because it has originally an N-ch open-drain
output.
Figure 5-66. Pin Configuration
Caution When data is received, the N-ch transistor must be turned off, so FFH must be written to
SIO beforehand. The N-ch open-drain output can be turned off at any time during transfer.
However, when the wake-up function specification bit (WUP) is set to 1, the N-ch transistor
is always off, so there is no need to write FFH to SIO before reception.
SO
R L
SI
SO
SI
SB0, SB1 SB0, SB1
Serial data bus
N-ch open-drain N-ch open-drain
(Clock input)
Clock output Clock input
(Clock output)
Serial clock
Master device
Slave device