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 Post subject: 6502 instruction cycles
PostPosted: Mon Feb 07, 2005 11:43 pm 
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Joined: Fri Nov 26, 2004 5:15 pm
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Location: Norway
i was checking up my instruction clk timings in my 6502 core in different documents to make sure they are 100% correct. But i found none of the documents agreed 100% on all instructions.

This is taken from the official 6502 manual, linked to from the wiki.
http://users.telenet.be/kim1-6502/6502/pm-apndx.html#b
this gives a nice listing of all the instructions and there clk cycles. If you then look at the table that are in appendix C in the same document (below the listing). This gives a short representation of the just clk cycles in a table, but the two dont agree on the cycles. One states that AND (..),Y dont get penalty for pagecrossing and the other states that it does but not for EOR (..), Y.

this is another listing from 6502.org
http://www.6502.org/tutorials/6502opcodes.html
this one claim the AND and ORA, Zero Page and Zero Page X adressing modes are 2 and 3 clk.

my original referance, before i started to check
http://www.obelisk.demon.co.uk/6502/reference.html
and this also has its own values for the instructions given above.

I currently use the timings from the last url since it is more consistant on the timings for different adressing mode. If anyone can confirm the correctness of these documents, this is welcome


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PostPosted: Tue Feb 08, 2005 7:52 am 
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Formerly Fx3
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Joined: Fri Nov 12, 2004 4:59 pm
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Location: Brazil
A few users has reported the 'obelisk.demon.co.uk' page as being the accurate resource. ;)

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Zepper
RockNES developer


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 Post subject:
PostPosted: Tue Feb 08, 2005 9:52 pm 
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Joined: Thu Feb 03, 2005 4:23 am
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obelisk is a very good resource in my opinion.


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PostPosted: Wed Feb 09, 2005 12:00 am 
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I'll third that.

Obelisk is my main reference page. I have yet to find an error in it.


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PostPosted: Wed Feb 09, 2005 5:30 am 
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Joined: Mon Sep 20, 2004 6:04 am
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Location: Indianapolis
Neat, I found an error in the (printed) book I have. Lists both ops $25 and $35 as "AND Zeropage". But it got the cycle counts right, heh.


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