UPD17072 datasheet(96/228 Pages) RENESAS

96 / 228 page

µPD17072,17073

12.3.3 Error of basic timer 1

As described in 12.3.2, the interrupt generated by basic timer 1 is accepted each time the basic timer 1 interrupt

pulse falls, if the EI instruction has been executed, and if the interrupt has been enabled.

Therefore, an error of basic timer 1 occurs only when any of the following operations are performed:

• When the first interrupt after basic timer 1 interrupt has been enabled has been accepted

• When the time interval at which the IRQBTM1 flag is to be set is changed, i.e., when the first interrupt is accepted

after the interrupt pulse has been changed

• When data has been written to the IRQBTM1 flag

Figure 12-9 shows an error in each of the above operations.

Figure 12-9. Error of Basic Timer 1 (1/2)

(a) When interrupt by basic timer 1 is enabled

At point <1> in the above figure, the interrupt by basic timer 1 is accepted as soon as the interrupt is

enabled.

At this time, the error is –tSET.

If an interrupt is enabled by the “EI” instruction at the next point <3>, the interrupt occurs at the falling edge

of the basic timer 1 interrupt pulse.

At this time, the error is:

–tSET < error < 0

<1> <2>

<3>

Interrupt pending

SET1 IPBTM1

Interrupt accepted

tSET

Basic timer 1

interrupt pulse

IRQBTM1 flag

IPBTM1 flag

INTE FF

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