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

Subject: Re: [stella] BRK instruction: Request for clarification!
From: "B. Watson" <atari@xxxxxxxxxxxxxx>
Date: Tue, 26 Jul 2005 10:21:05 -0400
> The B flag is wired directly to the interrupt input pin on the
> 6502. In the 6507 this pin is internally set high, so on the VCS
> the B flag should always be set.
> None of the instructions in the 6502 affects the B flag.
> It's hardwired to the interrupt input pin, so you can't change
> the bit yourself.

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.

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