UPD17062 datasheet(140/298 Pages) RENESAS

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138

µPD17062

12.3.2

Timer Error Caused by the BTM0CY Flag

There are two types of timer error that can occur because of the BTM0CY flag. One type depends on the

timing when the BTM0CY flag is checked, and the other type occurs when the timer carry FF setting interval

is changed.

These types of timer error are detailed below.

(1) Timer error by BTM0CY flag check timing

As described in Section 12.3.1, the time interval at which the BTM0CY flag is checked must be less than

the time interval at which the timer carry FF is set to 1.

Suppose the time interval at which the BTM0CY flag is checked is tCHECK, and the time interval (100 ms or

5 ms) at which timer carry FF is set is tSET. The relationship between these two intervals must be as follows:

tCHECK < tSET

Under this condition, as shown in Fig. 12-4, the timer error that depends on the timing when the BTM0CY

flag is checked is as follows:

0 < error < tCHECK

Fig. 12-4

Timer Error That Depends on the Time Interval at Which the BTM0CY Flag Is Checked

As shown in Fig. 12-4, when the BTM0CY flag is checked at

$, it appears to be 1 and causes the timer to

be updated. When it is checked at

%, it appears to be 0, and defers the updating of the timer until it is checked

again at

&. In this case, the timer count is increased by tCHECK3.

SKT1

BTM0CY

SKT1

BTM0CY

SKT1

BTM0CY

SKT1

BTM0CY

Timer carry FF set pulse

BTM0CY flag

tSET

tCHECK

tCHECK2

tCHECK3

UPD17062 Datasheet(PDF) 140 Page - Renesas Technology Corp