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: > > http://www.6502.org/tutorials/register_preservation.html > > 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, Dennis Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://stella.biglist.com
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