UPD17062 datasheet(147/298 Pages) RENESAS

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145

µPD17062

12.4.3

If the BTM0CY flag is checked at the same time with a CE reset

As described in Section 12.4.2, a CE reset occurs at the same time the BTM0CY flag is set to 1.

If the BTM0CY flag read instruction happens to occur at the same time a CE reset occurs, the BTM0CY flag

read instruction takes precedence.

Once a CE pin goes from a low to a high, if the setting of the BTM0CY flag (at the positive-going edge of

the timer carry FF set pulse) and a BTM0CY flag read instruction occur at the same time, a CE reset occurs

next time the BTM0CY flag is set.

This operation is shown in Fig. 12-7.

Fig. 12-7

Operation That Occurs When a CE Reset and a BTM0CY Flag Read Instruction Coincide

So, if your program checks the BTM0CY flag cyclically and the BTM0CY flag check time interval coincides

with the BTM0CY flag setting time interval, a CE reset will not occur forever.

Note the following point:

Because one instruction cycle is 2

µs (1/500 kHz), a program that checks the BTM0CY flag once at every 500

instructions reads the BTM0CY flag at every 1 ms (2

µs × 500).

Under this condition, whichever timer interval set pulse, 5 ms or 100 ms, is selected, a CE reset will not

occur for ever, once the setting and checking of the BTM0CY flag occur at the same time.

To be specific, avoid creating a cyclic program that satisfies the following condition.

tSET

× 500 = n (n is any integer)

where tSET : BTM0CY flag setting time interval

: BTM0CY flag read instruction cycle time x number of steps

In other words, the program should not contain x steps when the above calculation produces any integer.

SKT 1

BTM0CY

SKT 1

BTM0CY

CE reset

SKT1 BTM0CY

(PEEK…)

(SKT…)

CE pin

Timer carry FF

set pulse

BTM0CY flag

Timer carry FF set pulse

BTM0CY flag

Instruction

Built-in macro

2 s

If the BTM0CY flag is read

during this period, a CE

reset is deferred by one cycle.

Normally, the program starts at address 0000H at this

point, but a CE reset does occur because the program to

read the BTM0CY flag also happens to run.

PEEK WR, . MF. BTM0CY SHR 4

SKT WR, #, DF. BTM0CY AND 000FH

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