UPD17708 datasheet(252/356 Pages) NEC

252 / 356 page

252

µPD17704, 17705, 17707, 17708, 17709

16.3.7 Cautions on setting and reading data

Data is set to the presettable shift register 1 by using the “PUT SIO1SFR, DBF” instruction.

To read the data of this register, the “GET DBF, SIO1SFR” instruction is used.

Set or read data of the register in the wait status. If the wait status is released, data may not be correctly set or

read depending on the status of the shift clock pin.

The following table shows the data setting and reading timing, and points to be noted.

Table 16-8. Reading and Writing Data of Presettable Shift Register and Cautions

Status on Execution

Status of Shift

Serial I/O Mode

of PUT/GET

Clock Pin

Wait

Read (GET)

• External clock:

Normal write

status

Write (PUT)

floating

Normal write

• Internal clock:

Outputs contents of MSB when wait status is released next time and shift clock

output latch

pin falls (during transmission)

(always high)

Wait

Read (GET)

High level

Cannot be read normally

released

Contents of SIO1SFR are lost

status

Low level

Normal write

Write (PUT)

High level

Normal write

Outputs contents of MSB at which PUT instruction has been executed.

Clock counter is not reset

Low level

Cannot be read normally

Contents of SIO1SFR are lost

Data

MSB

Wait released

PUT SIO1SFR, DBF

Clock

Data

MSB

PUT SIO1SFR, DBF

Clock

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