Date   : Tue, 26 Feb 2008 16:47:52 +0000
From   : adsb@... (Andrew Benham)
Subject: BBC FPGA Boots to BASIC... almost...

Tom Walker wrote:

> No need. The BRK flag doesn't actually exist in the CPU - it's only present
> when the status is pushed, where it is clear for an IRQ and set at all other
> times.
> If the FPGA 6502 gets this wrong, that could be one problem. Another problem
> could be if it fails to disable interrupts on a BRK - that might crash it
> also.

The last part of the web page
    http://www.6502.org/tutorials/register_preservation.html
is worth a read.
(Starting with 'The B (Break) flag, bit 4 of the P (Processor status) register,
  is a frequent source of confusion on the 6502.')

-- 
Andrew Benham           adsb@...       
Southgate, London N14, United Kingdom

The gates in my computer are AND OR and NOT, not "Bill".