NEC PD78F9488 User Manual
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CHAPTER 11 SERIAL INTERFACE 20
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User’s Manual U15331EJ4V1UD
(2) Communication
operation
In 3-wire serial I/O mode, data transmission/reception is performed in 8-bit units. Data is transmitted/
received bit by bit in synchronization with the serial clock.
Transmit shift register 20 (TXS20/SIO20) and receive shift register 20 (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 receive buffer
register 20 (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.
Figure 11-11. 3-Wire Serial I/O Mode Timing (1/2)
(i) Master operation timing (CSCK20=0)
1
2
3
4
5
6
7
8
DO7
DO6
DO5
DO4
DO3
DO2
DO1
DO0
DI7
DI6
DI5
DI4
DI3
DI2
DI1
DI0
SCK20
SO20
Note
SI20
SIO20
write
INTCSI20
Note The value of the last bit previously output is output.