I recommend these two books for 6502 assembly: https://archive.org/details/ataribooks-machine-language-for-... (https://archive.org/details/ataribooks-machine-language-for-beginners/mode/2up) and https://archive.org/details/ataribooks-the-second-book-of-ma... (https://archive.org/details/ataribooks-the-second-book-of-machine-language) These two books will give you a good understanding of 6502 assembler - it is general but gives a good background and has a nice assembler with a full walk through of the code. I used these two books to learn 6502 on my Commodore 64 and they are highly recommended.
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