Re: Is it possilble to use timer interrupt in Apple II?

["Michael J. Mahon" <mjmahon@aol.com>]

bluebird wrote:
> I want to use timer interrupt in Apple II/Apple II+/Apple IIe.
> For example, I want to install 300ms timer interrupt and want its ISR
> called periodically.
>
> Is there any example?

There is no timer interrupt standardized across all Apple II systems.

Only the Apple IIc (of the systems you mention) has a built-in timer
interrupt--at the vertical blanking rate, or 60Hz.  All other systems
in your list have this interrupt only if a mouse card is installed, or
some other card that can generate interrupts.

If the machine has an interrupt source, then only the ProDOS operating
system has standard provisions for handling interrupts.  All interrupts
are handled in one ISR chain, and your ISR must "claim" its desired
interrupt by recognizing and processing it.  There is no "vectoring".

-michael

NadaNet and AppleCrate II: parallel computing for Apple II computers!
Home page: http://home.comcast.net/~mjmahon

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