CHAPTER 9 SERIAL INTERFACE 00
User's Manual U11919EJ3V0UM00
148
(2)
Communication operation
In the 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 00 (TXS00/SIO00) and receive shift register 00 (RXS00) shift operations are
performed in synchronization with the fall of the serial clock (SCK0). Then transmit data is held in the SO0
latch and output from the SO0 pin. Also, receive data input to the SI0 pin is latched in receive buffer
register 00 (RXB00/SIO00) on the rise of SCK0.
At the end of an 8-bit transfer, the operations of TXS00/SIO00 and RXS00 stop automatically, and the
interrupt request signal (INTCSI0) is generated.
Figure 9-11. 3-Wire Serial I/O Mode Timing
1
2
3
4
5
6
7
8
DI7
DI6
DI5
DI4
DI3
DI2
DI1
DI0
DO7
DO6
DO5
DO4
DO3
DO2
DO1
DO0
End of Transfer
Transfer start at the falling edge of SCK0
SCK0
SI0
SO0
INTCSI0
(3)
Transfer start
Serial transfer is started by setting transfer data to transmit shift register 00 (TXS00/SIO00) when the
following two conditions are satisfied.
•
Serial operation mode register 00 (CSIM00) bit 7 (CSIE00) = 1
•
Internal serial clock is stopped or SCK0 is at high level after 8-bit serial transfer.
Caution
If CSIE00 is set to "1" after data write to TXS00/SIO00, transfer does not start.
A termination of 8-bit transfer stops the serial transfer automatically and generates the interrupt request
signal (INTCSI0).
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