Re: [stella] BRK instruction: Request for clarification!

Subject: Re: [stella] BRK instruction: Request for clarification!
From: "Dennis Debro" <dennis@xxxxxxxxxxxxxxx>
Date: Tue, 26 Jul 2005 10:39:42 -0400
Hi there,

> You sure about that?
> If you're right, someone needs to fix this tutorial:
> It claims that:
>     The B (Break) flag, bit 4 of the P (Processor status) register, is a
>     frequent source of confusion on the 6502. The sole purpose of this
> flag
>     is to distinguish a BRK from a IRQ.
> ...which is what I always thought it was for, too... but I'm none too
> confident that I know what I'm talking about, since I haven't actually
> used any of this interrupt-related stuff in 15+ years.

IIRC the b flag is set when a BRK is done and it's cleared on an IRQ/NMI.
Since the 2600 doesn't have hardware IRQ or NMI capability the b status
would always be set after a BRK.

Take care,

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