NEC mPD789426 Series User Manual page 240

(2) Communication operation
In 3-wire serial I/O mode, data transmission/reception is performed in 8-bit units.
transmitted/received bit by bit in synchronization with the serial clock.
Transmission shift register (TXS20/SIO20) and reception shift register (RXS20) shift operations are
performed in synchronization with the fall of the serial clock (SCK20). Then transmit data is held in the
SO20 latch and output from the SO20 pin. Also, receive data input to the SI20 pin is latched in the
reception buffer register (RXB20/SIO20) on the rise of SCK20.
At the end of an 8-bit transfer, the operation of TXS20/SIO20 and RXS20 stops automatically, and the
interrupt request signal (INTCSI20) is generated.
(i) Master operation timing (when DAP20 = 0, CKP20 = 0, SSE20 = 0)
SIO20
write
SCK20
SO20
Note
SI20
INTCSI20
Note The value of the last bit previously output is output.
240
CHAPTER 12 SERIAL INTERFACE 20
Figure 12-11. 3-Wire Serial I/O Mode Timing (1/7)
1 2 3
DO7 DO6 DO5
DI7 DI6 DI5
User's Manual U15075EJ1V0UM00
4 5 6
DO4 DO3 DO2
DI4 DI3 DI2
Data is
7 8
DO1 DO0
DI1 DI0