Wire Serial I/O Mode Timings - NEC PD78056F User Manual

(2) Communication operation
The 3-wire serial I/O mode is used for data transmission/reception in 8-bit units. Bit-wise data transmission/
reception is carried out in synchronization with the serial clock.
Shift operation of the serial I/O shift register 1 (SIO1) is carried out at the falling edge of the serial clock SCK1.
The transmit data is held in the SO1 latch and is output from the SO1 pin. The receive data input to the SI1
pin is latched into SIO1 at the rising edge of SCK1.
Upon termination of 8-bit transfer, the SIO1 operation stops automatically and the interrupt request flag
(CSIIF1) is set.
SCK1
SI1
SO1
CSIIF1
SIO1 Write
Caution SO1 pin becomes low level by SIO1 write.
(3) MSB/LSB switching as the start bit
The 3-wire serial I/O mode enables to select transfer to start from MSB or LSB.
Figure 18-7 shows the configuration of the serial I/O shift register 1 (SIO1) and internal bus. As shown in the
figure, MSB/LSB can be read/written in reverse form.
MSB/LSB switching as the start bit can be specified with bit 6 (DIR) of the serial operating mode register 1
(CSIM1).
CHAPTER 18 SERIAL INTERFACE CHANNEL 1
Figure 18-6. 3-Wire Serial I/O Mode Timings
1 2 3
DI7 DI6 DI5
DO7 DO6 DO5
Transfer Start at the Falling Edge of SCK1
4 5 6
DI4 DI3 DI2
DO4 DO3 DO2
7 8
DI1 DI0
DO1 DO0
End of Transfer
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