UPD17708 datasheet(154/356 Pages) NEC

154 / 356 page

µPD17704, 17705, 17707, 17708, 17709

154

13.2.5 Errors of basic timer 0

Errors of basic timer 0 include an error due to the detection time of the BTM0CY flag, and an error that occurs

when the time interval at which the BTM0CY flag is to be set is changed.

The following paragraphs (1) and (2) describe each error.

(1) Error due to detection time of BTM0CY flag

The time to detect the BTM0CY flag must be shorter than the time at which the BTM0CY flag is set (refer

to 13.2.6 Notes on using basic timer 0).

Where the time interval at which the BTM0CY flag is detected is tCHECK and the time interval at which the

flag is set is tSET (100, 50, 20, or 10 ms), tCHECK and tSET must relate as follows.

tCHECK < tSET

At this time, the error of the timer when the BTM0CY flag is detected is as follows, as shown in Figure

13-5.

0 < Error < tSET

Figure 13-5. Error of Basic Timer 0 due to Detection Time of BTM0CY Flag

As shown in Figure 13-5, the timer is updated because BTM0CY flag is “1” when it is detected in step

<2>.

When the flag is detected next in step <3>, it is “0”. Therefore, the timer is not updated until the flag is

detected again in <4>.

This means that the timer is extended by the time of tCHECK3.

BTM0CY flag

setting pulse

tSET

tCHECK1

SKT1

BTM0CY

<1>

SKT1

BTM0CY

<2>

SKT1

BTM0CY

<3>

SKT1

BTM0CY

<4>

tCHECK2

tCHECK3

BTM0CY flag

UPD17708 Datasheet(PDF) 154 Page - NEC