UPD17708 datasheet(157/356 Pages) NEC

157 / 356 page

157

µPD17704, 17705, 17707, 17708, 17709

13.2.6 Cautions on using basic timer 0

(1) BTM0CY flag detection time interval

Keep the time to detect the BTM0CY flag shorter than the time at which the BTM0CY flag is set.

This is because, if the time of processing B is longer than the time interval at which the BTM0CY flag

is set as shown in Figure 13-8, setting of the BTM0CY flag is overlooked.

Figure 13-8. BTM0CY Flag Detection and BTM0CY Flag

(2) Timer updating processing time and BTM0CY flag detection time interval

As described in (1) above, time interval tSET at which the BTM0CY flag is detected must be shorter than

the time for which to set the BTM0CY flag.

At this time, even if the time interval at which the BTM0CY flag is detected is short, if the updating

processing time of the timer is long the processing of the timer may not be executed normally at CE reset.

Therefore, the following condition must be satisfied.

tCHECK + tTIMER < tSET

tCHECK : time to detect BTM0CY flag

tTIMER : timer updating processing time

tSET

: time to set BTM0CY flag

An example is given below.

BTM0CY flag

setting pulse

BTM0CY flag

SKT1 BTM0CY SKT1 BTM0CY

Processing A

Processing B

SKT1 BTM0CY

tSET

<1>

<2>

<3>

<4>

<5>

Because execution time of processing B takes too long

after detection of BTM0CY flag that has been set to “1”

in <2>, BTM0CY flag that is set to “1” in <3> cannot be

detected.

UPD17708 Datasheet(PDF) 157 Page - NEC