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6502 Microprocessor

A guide to 6502 processor assembly

(by commodore)

6502 Processor Manual

This article is online from 3245 days and has been seen 5166 times


6502 Microprocessor

Most of the following information has been taking out of the "Commodore 64
Programmers Reference Manual" simply because it was available in electronic
form and there appears to be no difference between this documentation and
the 6502 documentation, they are both from the 6500 family after all. I've
made changes and additions where appropriate.

In theory you should be able to use any code you can find for emulating
the 6510 (the C64 processor).



THE REGISTERS INSIDE THE 6502 MICROPROCESSOR

Almost all calculations are done in the microprocessor. Registers are
special pieces of memory in the processor which are used to carry out, and
store information about calculations. The 6502 has the following registers:


THE ACCUMULATOR

This is THE most important register in the microprocessor. Various ma-
chine language instructions allow you to copy the contents of a memory
location into the accumulator, copy the contents of the accumulator into
a memory location, modify the contents of the accumulator or some other
register directly, without affecting any memory. And the accumulator is
the only register that has instructions for performing math.


THE X INDEX REGISTER

This is a very important register. There are instructions for nearly
all of the transformations you can make to the accumulator. But there are
other instructions for things that only the X register can do. Various
machine language instructions allow you to copy the contents of a memory
location into the X register, copy the contents of the X register into a
memory location, and modify the contents of the X, or some other register
directly.


THE Y INDEX REGISTER

This is a very important register. There are instructions for nearly
all of the transformations you can make to the accumulator, and the X
register. But there are other instructions for things that only the Y
register can do. Various machine language instructions allow you to copy
the contents of a memory location into the Y register, copy the contents
of the Y register into a memory location, and modify the contents of the
Y, or some other register directly.

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 Tags: 6502, commodore


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