Electronics America Single-Chip Microcontrollers User's Manual

CHAPTER 11 SERIAL INTERFACE 20

214 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

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)

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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.