NEC 78014Y Series User Manual page 342

(2) Communication operation
The 3-wire serial I/O mode is used for data transmission/reception in 8-bit units. Data transmission/reception
is carried out bit-wise in synchronization of the serial clock.
Shift operation of the serial I/O shift register 0 (SIO0) is carried out at the falling edge of the serial clock (SCK0).
The transmitted data is held in the SO0 latch and is output from the SO0 pin. The received data input to the
SI0 pin is latched in SIO0 at the rising edge of SCK0.
Upon termination of 8-bit transfer, SIO0 operation stops automatically and the interrupt request flag (CSIIF0) is
set.
SCK0
SI0
SO0
CSIIF0
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The SO0 pin serves for CMOS output and generates the SO0 latch status. Thus, the SO0 pin output status can
be manipulated by setting bit 0 (RELT) and bit 1 (CMDT) of the serial bus interface control register (SBIC).
However, do not carry out this manipulation during serial transfer.
Control the SCK0 pin output level in the output mode (internal system clock mode) by manipulating the P27 output
latch (refer to 16.4.8 SCK0/SCL/P27 pin output manipulation).
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CHAPTER 16 SERIAL INTERFACE CHANNEL 0 ( µ PD78014Y Subseries)
Figure 16-9. 3-Wire Serial I/O Mode Timings
1 2 3
DI7 DI6
DO7 DO6
Transfer Start at the falling edge of SCK0
4 5 6
DI5 DI4 DI3
DO5 DO4 DO3
7 8
DI2 DI1 DI0
DO2 DO1 DO0
End of Transfer