
237
μ
PD17704, 17705, 17707, 17708, 17709
(3) Operation of clock counter
The value of the clock counter is incremented from the initial value “0” each time the rising of the clock pin
has been detected.
The value of the clock counter returns to “0” after it has reached “8”, and the clock counter continues counting.
The clock counter is also reset in the following cases.
At reset (power-ON reset, WDT&SP reset, CE reset)
On execution of clock stop instruction
If data is written to serial I/O0 wait control register
If communication mode is changed from 2-wire or 3-wire serial I/O mode to I
2
C bus mode
(4) Wait operation and Cautions
When the wait status is released, serial data is output (during transmission operation) at the falling of the next
clock, and the wait status is kept released until a condition (wait condition) set by the SIO0WRQ0 and 1 flags
is satisfied.
When the wait condition is satisfied, the shift clock pin is made high, and the operations of the clock counter
and presettable shift register 0 are stopped.
The value of the presettable shift register 0 cannot be read correctly if it is read while the wait status is released
and while the shift clock pin is high.
Correct data cannot be written to the presettable shift register 0 while the wait status is released and while
the shift clock pin is low.
If the forced wait status is specified while the wait status is released, the forced wait status is set as soon as
“0” has been written to the SIO0NWT flag.
The clock output wave is not affected even if the wait status is released again when it has been already released
once. Note, however, that the clock counter is reset.
(5) Interrupt request issuance timing
Interrupt request issuance timing can be selected by the SIO0IMD0 and 1 flags.
For details, refer to
16.2.7 Interrupt control block
.
(6) Acknowledge block and its operation
The acknowledge block operates only in the I
2
C bus mode.
(7) Shift clock generation timing in serial I/O mode
(a) On releasing wait status from initial status
The initial status is the status when the internal clock operation in the serial I/O mode has been selected.
In the wait status, a high level is output to the shift clock pin.