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

[dempson@actrix.gen.nz (David Empson)]

bluebird <mildstorm@gmail.com> 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?

The Apple II/II+/IIe doesn't have any built-in hardware which can
generate a periodic interrupt.

You can gain some form of timed interrupt with many expansion cards, but
the degree of control over the period of the interrupt may be limited.

For example, the Apple II Mouse Card can generate a screen refresh
interrupt (60 Hz in an NTSC II/II+/IIe, probably 50 Hz in a PAL IIe).

Some clock cards can also generate timed interrupts but they may be
limited to 1 Hz or a specific set of higher frequencies, and may require
changing jumpers or DIP switches to enable or configure the interrupt.

A more general purpose I/O expansion card containing a VIA chip could
generate arbitrary periodic interrupts under program control.

I expect that something like the Carte Blanche could also do this, if
someone has set up an appropriate configuration for it.

-- 
David Empson
dempson@actrix.gen.nz