Caple C871i Manuel d'utilisateur télécharger pdf (Page 503)

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101

Apple II Computer Info

Only one of the four interrupts in each group may be enabled. The 1

hour, 1 minute and 1 second interrupts generate a pulse of 122.1

millisecond duration on the appropriate interrupt line. The 1024 Hz

interrupt generates a pulse of 488 microseconds every 976 microseconds.

It is a very bad idea to have NMI enabled, because an NMI can occur at

any time, even while the processor has interrupts disabled. The worst

example of this is during a disk write operation: an NMI can cause

part of the disk's contents to be destroyed!

The IRQ is less dangerous. If the processor has interrupts enabled, an

IRQ from the card will cause the interrupt handler to be called

immediately (you can install up to four interrupt handlers if you are

running ProDOS).

It is normal practice for an interrupt handler to check that the

interrupt comes from its device. This is a little difficult to do with

the Time ][ card, but not impossible.

If no interrupt handler has been installed for the Time ][, an

interrupt from the card will immediately crash the computer (as you

have discovered). Interrupts are normally disabled (within the

processor) until you run a communications program or boot ProDOS-8 1.2

or later.

David Empson

[email protected]

Snail mail: P.O. Box 27-103, Wellington, New Zealand

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Apple II Computer Technical Information : Apple II Family Hardware Info

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Caple C871i Manuel d'utilisateur Page 503

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Caple C871i Manuel d'utilisateur Page 503

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