All Questions
7
questions
18
votes
2
answers
4k
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Did the NES CPU save die area by omitting BCD?
The NES CPU was a copy of the 6502 with the BCD circuitry removed. As I understand it, this modification was motivated by a theory that BCD was the only part of the 6502 that was actually patented, so ...
- 63.1k
19
votes
3
answers
5k
views
What is the purpose of mirrored memory regions in NES's CPU memory map? [duplicate]
[Please see answers to this related question as well]
I've started reading the "official" NES Documentation and in page ten, it says that "memory locations $0000-$07FF are mirrored ...
- 193
4
votes
4
answers
595
views
Would having the console's CPU help in emulation hypothetically?
If I had a hypothetical computer just like nowaday's computers, but it had an NMOS 6502, would it provide me with a better emulation experience than if I were to emulate the 6502 inside software? Also,...
- 121
17
votes
4
answers
2k
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Best way to locate data on ROM? (6502 Processor)
Lately I've been interested in how old machines work, in particular an NES. While there are quite a few resources on the basic operations and even some games that have been totally broken down byte by ...
- 173
14
votes
1
answer
4k
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What is the relationship between the Ricoh 2A03 and the MOS 6502?
The Ricoh 2A03 (and the 2A07) is the CPU in the well-known Nintendo Entertainment System. Apparently, the die is very similar indeed, as the slides in this video suggest https://www.youtube.com/watch?...
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19
votes
2
answers
2k
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Is it possible to procedurally determine the number of cycles a particular instruction takes on a 6502?
Most emulators store the number of cycles a particular instruction takes in an array, and then adds any conditional cycles if needed (when crossing page boundaries, for example).
I'm wondering if ...
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94
votes
7
answers
29k
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Why would a NES game use an undocumented 1-byte or 2-byte NOP in production?
Reading the NESdev wiki page on CPU unofficial opcodes, I see a few games use an undocumented 2-byte NOP instuction in production: Puzznic, F-117A Stealth Fighter, and Infiltrator use $89 #i. Beauty ...
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