383
CHAPTER 18 SERIAL INTERFACE CHANNEL 0 (
µ
PD78078Y Subseries)
(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 0 (SIO0) is carried out at the falling edge of the serial clock
(SCK0). The transmitted data is held in the SO0 latch and is output from the SO0 pin. The received data
input to the SI0 pin is latched in SIO0 at the rising edge of SCK0.
Upon termination of 8-bit transfer, SIO0 operation stops automatically and the interrupt request flag (CSIIF0)
is set.
Figure 18-7. 3-Wire Serial I/O Mode Timings
The SO0 pin is a CMOS output pin and outputs current SO0 latch statuses. Thus, the SO0 pin output status
can be manipulated by setting the bit 0 (RELT) and bit 1 (CMDT) of the serial bus interface control register
(SBIC). However, do not carry out this manipulation during serial transfer.
Control the SCK0 pin output level in the output mode (internal system clock mode) by manipulating the P27
output latch (refer to 18.4.7 SCK0/SCL/P27 pin output manipulation).
(3) Other signals
Figure 18-8 shows RELT and CMDT operations.
Figure 18-8. RELT and CMDT Operations
RELT
CMDT
SO0 latch
SI0
SCK0
1
2
3
4
5
6
7
8
DI7
DI6
DI5
DI4
DI3
DI2
DI1
DI0
SO0
DO7
DO6
DO5
DO4
DO3
DO2
DO1
DO0
CSIIF0
Transfer Start at the Falling Edge of SCK0
End of Transfer
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