Re: LZ: RST

Subject: Re: LZ: RST
From: barrym <barrym@neosoft.com>
Date: Wed, 31 Jul 1996 18:57:37 -0500 (CDT)
In-Reply-To: <199607310820.KAA16013@defiant.rbk.sollentuna.se>

On Wed, 31 Jul 1996, David Kristensen wrote:

> What exactly does the RST instruction mean/stand for/do, etc? I haven't come
> across it in computer assembly (but I know less about that than I do z80, so
> that doesn't say much). Does it just call a function on rom page 0? (oh
> yeah, if it does, do I need to make sure that the rom page is on 0, or will
> it do that automatically?). Any answers would be appreciated (well, almost
> any answers...:)

What's the difference in computer assembly and Z80?

RST is a software interrupt.  It stands for ReSTart according
to my book.  There are 8 addresses in lower memory that
correspond to the RST numbers.  When RST is encountered
the PC is pushed onto the stack and execution continues at
one of the 8 addresses, depending on the RST number.

Those addresses are in rom and usually contain jumps
to other rom areas.  Just what each RST does is dependant
on the rom.

When I did some Z80 programming around 79 or 80, this was
called BRK, if I remember correctly.  It was just a different
mnemonic for the same instruction.  I'm not 100% sure I'm
not confusing this with another cpu though.

Barry

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