Re: APPLE IIe IRQ HANDLER LOCATION

[Rubywand <rubywand@swbell.net>]

jborsheim@hotmail.com writes ...
> 
> I am making the big upgrade from the apple II to the IIe.  The irq
> handler has moved from FA86 to where?  (If mem locations FFFE and FFFF
> still point to the irq handler then is it located at C3FA??)   The old
> user routine vector in ram was at 03FE, 03FF.  Where is the user
> routine vector location in the IIe??


     According to the 'IIe Technical Reference ROM listing, $C3FA is
where execution gets sent first for IRQ interrupts.

     The manual identifies $03FE, $03FF as the "User Interrupt" address.
One new consideration is the existence of built-in ROM stuff in the
$C3xx area which includes part of the IRQ interrupt-handler code.

    The manual notes that, if a peripheral card wants to execute code in
its own $C8xx area and does not want to shut down IRQ response, it
should place its Slot address in MSLOT ($07F8) because, should there be
an IRQ, the $C3xx interrupt code will execute and this will
automatically switch the $C8xx address space to that associated with
Slot 3. When it's done, the interrupt handler uses the MSLOT info to
switch ON the correct $C8xx area and return control to the routine which
was interrupted.  


Rubywand