[A83] Re: Explaining the stack for registers

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[A83] Re: Explaining the stack for registers


Sure...

  push  hl
  call  routine
  ...           ; don't pop

routine:
  pop   hl      ; return address in HL
  ex    (sp),hl ; return address on stack, pushed HL back in HL
  ...
  ret           ; safe to return

>From: "Ronald Teune" <rtwolf@gmx.net>
>Reply-To: assembly-83@lists.ticalc.org
>To: <assembly-83@lists.ticalc.org>
>Subject: [A83] Re: Explaining the stack for registers
>Date: Fri, 17 Aug 2001 21:45:31 +0200
>
>
> >Also note that CALL and RET also use the same stack...
> >
> >You can't:
> >
> >  push hl
> >  call Routine
> >
> >Routine:
> >  pop hl
> >  ret
>
>But is there ANY way to push/pop through calls?
>
> >If you did that, HL would contain the address of the code after the call,
> >and the RET would jump to the value of the pushed HL.  In other words,
> >CRASH.
> >
> >(Unless of course HL contained a valid executable address...)
> >
> >>From: "TypeR unknown" <typerfuture@hotmail.com>
> >>Reply-To: assembly-83@lists.ticalc.org
> >>To: assembly-83@lists.ticalc.org
> >>Subject: [A83] Re: Explaining the stack for registers
> >>Date: Thu, 16 Aug 2001 19:51:46 +0200
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> >>
> >>
> >>Ahh I understand much better now!!!
> >>I thought that every register that can be pushed had it's own stack, so 
>I
> >>was a bit confused when it appeared that the content of one register 
>could
> >>somehow be loaded in another register, but I understand very well now,
> >>thank
> >>you very much for your explanation!
> >>
> >>
> >> >From: "Michael Vincent" <hookman@worldnet.att.net>
> >> >Reply-To: assembly-83@lists.ticalc.org
> >> >To: <assembly-83@lists.ticalc.org>
> >> >Subject: [A83] Re: Explaining the stack for registers
> >> >Date: Thu, 16 Aug 2001 10:12:18 -0700
> >> >
> >> >
> >> >First, "if you push af and then pop bc" the contents will be in BC, 
>not
> >>AF.
> >> >The reason for this is when you push a register, the values in it are
>put
> >> >on
> >> >the stack, not the name. So if you push af then the value of A and the
> >> >flags
> >> >byte are on the stack. You can then pop whatever you want. If you pop 
>bc
> >> >then the 2 bytes on the stack from the push af will be put in BC. (B
>will
> >> >have what was in A, and C will have what was in F).
> >> >
> >> >There is no limit to how many times a register can be pushed, except 
>on
> >>the
> >> >TI-83 Plus (and I think 83) the stack is only 400 bytes. After that 
>you
> >> >will
> >> >corrupt RAM. The TI-OS uses a few bytes, but you have like 100 pushes 
>or
> >> >more you could do before you overflowed the stack.
> >> >
> >> >
> >> >Michael Vincent
> >> >Detached Solutions - www.detacheds.com
> >> >Radical Software - www.radicalsoft.org
> >> >
> >> >----- Original Message -----
> >> >From: "TypeR unknown" <typerfuture@hotmail.com>
> >> >To: <assembly-83@lists.ticalc.org>
> >> >Sent: Thursday, August 16, 2001 10:00 AM
> >> >Subject: [A83] Explaining the stack for registers
> >> >
> >> >
> >> > >
> >> > > After reading the FAQ in AsmGuru there is a question about the 
>stack
> >> >with
> >> > > registers. It says that (if I remember correctly) "if you push af 
>and
> >> >then
> >> > > pop bc, the contents of bc will be in af"
> >> > >
> >> > > WHY ???
> >> > >
> >> > > I see no logic in that, and unfortunatly it isn't explained in
>AsmGuru
> >> > > either, so here I am :)
> >> > >
> >> > > Also I would like to know how many times a register can be pushed.
> >> > >
> >> > >
> >> > >
> >> > >
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> >> >
> >> >
> >> >
> >>
> >>
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