Re: A86: User interrupt question


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Re: A86: User interrupt question




At 07:32 1998-04-04 -0500, you wrote:
>1.  Can you have an interrupt durring and interrupt?  Is this limit by the
>number of clock cycles in my interrupt?

Actually, that depends on WHAT interrupt you mean... the Z80 on the TI-86
only has one interrupt (INT), and then the answer is YES.

However, when an INT occurs, the IFF flags are cleared (= DI),
so unless you enable the interrupts (EI), no interrupt will interrupt
your current interrupt handler :-) As you may have noticed, the
interrupt handler at $38 ends with

 EI
 RETI

That EI is necessary.

Thus there is no way to know if you're "inside" an interrupt handler
or not - the status of the Z80 is the same as when you execute a DI
instruction.

>2.  Can I use regular ROM calls in:
>        1. The user interrupt and all other user areas?
>        2. The interrupt using IM 2 and the 257 byte table?

Well, yes, but some routines are probably not so smart to call
if you intend to make a TSR program that is active in the TI-OS
(for instance, variable routines). The most important thing should
be to preserve the current pages at $4000-$7FFF and $8000-$BFFF.

--
Real name: Jimmy Mårdell                 
IRC......: Yarin                         
Email....: mailto:yarin@acc.umu.se      <-- NEW E-MAIL ADDRESS!!!!
Homepage.: http://www.algonet.se/~mja/


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