UPD17708 datasheet(279/356 Pages) NEC

279 / 356 page

279

µPD17704, 17705, 17707, 17708, 17709

18.3.2 Operation of gate when IF counter function is selected

(1) When gate time of 1, 4, or 8 ms is selected

The gate is opened for 1, 4, or 8 ms from the rising of the internal 1-kHz signal after the IFCSTRT flag has

been set to 1, as illustrated below.

While this gate is open, the frequency input from a selected pin is counted by a 16-bit counter.

When the gate is closed, the IFCG flag is cleared to 0.

The IFCGOSTT flag is automatically set to 1 when the IFCSTRT flag is set.

(2) When gate is open

If opening of the gate is selected by the IFCCK1 and IFCCK0 flags, the gate is opened as soon as its opening

has been selected, as illustrated below.

If the counter is started by using the IFCSTRT flag while the gate is open, the gate is closed after undefined

time.

To open the gate, therefore, do not set the IFCSTRT flag to 1.

However, the counter can be reset by the IFCRES flag.

Sets IFCCK1 = IFCCK0 = 1

Gate is actually opened at this point.

If gate is opened while IFCGOSTT flag is 1, it is closed after undefined time

Count period

Gate is closed after undefined time if IFCSTRT flag is set during this period

Internal 1 kHz L

OPEN

Gate

The gate is opened or closed in the following two ways when opening the gate is selected as the gate time.

Gate is actually opened at this point

Count period (IFCGOSTT flag = 1)

IFCSTRT flag is set

IFCGOSTT flag is set at this point

End of counting

IFGOSTT flag is cleared

Internal 1 kHz

1 ms

Gate time

4 ms

8 ms

OPEN

UPD17708 Datasheet(PDF) 279 Page - NEC