Date   : Wed, 17 Mar 1999 10:27:28 GMT
From   : Adam Hamilton x8712 <Adam_Hamilton@...>
Subject: 6502 CPU - clock cycles

I am writing a 6502 emulator but I'm a little confused about
when I should add a clock cycle for crossing a page boundary.

Certain commands take an extra clock cycle if 'a page boundary is crossed'.
Which of the following examples (or both) would be classed as crossing
a page boundary?

1) 0AFF:  A9 00    LDA #&00

   The operand is located on a different page to the opcode, therefore
   a page boundary is crossed, yes?

2) 0AFE:  A9 00    LDA #&00

   Both the opcode and operand are on page 0A but the PC ends up pointing
   to 0B00 - does this also mean a page boundary has been crossed?


Thanks,

Adam Hamilton
Digital EDA Software Engineer
ASIC Technology

    _/_/  _/_/  _/  _/_/_/  _/_/_/  _/   E-Mail  : Adam_Hamilton@...
   _/  _/  _/  _/    _/    _/      _/    Address : MITEL Semiconductor,
  _/      _/  _/    _/    _/_/_/  _/               Swindon, Wilts.  UK.
 _/      _/  _/    _/    _/      _/      Phone   : +44/0 1793 518712
_/      _/  _/    _/    _/_/_/  _/_/_/   Fax     : +44/0 1793 518755