Re: [stella] 6507 question about vcs 2600 code

Subject: Re: [stella] 6507 question about vcs 2600 code
From: Chris Wilkson <ecwilkso@xxxxxxx>
Date: Thu, 8 Apr 2004 08:27:35 -0400 (EDT)

The 6507 is just a 6502 in a different package.  It does have
interrupt capabilities on the die.  Those pads are just not bonded out to
external pins.  So although the vcs isn't designed with hardware interrupts
in mind, in some perverse universe where noise was really bad, you could get
an interrupt triggered by accident.  I can't imagine a real world case where
this would happen, but it's theoretically possible.  A robust design would
call for the SEI.  Yet another tradeoff between bits and quality!

Weird science...

-Chris (who knows every byte is sacred, but...)

On Thu, 8 Apr 2004, Thomas Jentzsch wrote:

> Chris wrote: > Maybe it's a stupid question (If it is I apologize for
> this) > but I don't understand why some 2600 programs (e.g. Combat) > are
> using the SEI instruction at the begining of their code ? > > As far as I
> know the 6507 has no interrupt inputs. > > Have I missed something ? No,
> probably they just didn't know any better back then. SEI is not
> necessary. BTW: No HTML-mails please! Have fun! Thomas
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