I have to study microprocessors (6502)in order to complete my HNC in England. When I look at the codes, etc they look like a menu from a korean restaurant or an alien warning! Since I have not done this type of thing before I am requiring some HELP. I have a set of op codes for the 6502 we are using but I am unsure how to use them.What does BCS mean why do I need to EOR ,etc? Does anyone out there in good old 6502 land have any pointers or tips as to where I can get to the bottom of this alien warning.ANY assistance would be appreciated.
Regards
Ronnie

Ronnie,

The first thing to do is find a book (any book) on 6502 programming. They will be hard to find because the last ones wrote were in, something like, 1986 or so. EBay is a good place, but there are also some tutorials online. Check out www.6502.org as a good starting place for code, projects, etc....

If you already have a listing of the ops codes, do you also have a list of what they stand for? I'm guessing not, because then you would know what BCS means.....

if you look on www.6502.org, you should be able to find a Freeware assembler, which you will need to assemble the code that you do write, as well as a simulator to run the code if you don't have any hardware....

Tony

I responded to Ronnie privately right after he made his original post, telling him some things I've mentioned here before. For newcomers, I might reiterate that there's a wealth of info on this forum if you go back through the archives. Clicking on "Messages" shows a list that may seem overwhelming. It will take a couple of evenings or more to go through it all, but chances are good that your questions have already been asked and answered. We're glad to help anyway, which is why I answered privately instead of not at all.

With that said, I will add here that I just remembered that you will also find some of the information you were asking about, Ronnie, at www.6502.org/tutorials/6502opcodes.htm . Unfortunately, this one only covers the old NMOS 6502. It does not have any of the new instructions or addressing modes that came with the CMOS version (the 65c02), let alone those that came with later refinements, such as stopping the processor to save power and be ready to respond faster when an interrupt hits, or BBS & BBR, which let you test a bit in memory and do a relative conditional branch all in a single 3-byte 5-clock instruction. It also has notes that only apply to the old NMOS 6502 and not the 65c02. One I remember warns of the problem with having a JMP-indirect instruction start at address xxFE, two bytes before a page boundary. (This makes the NMOS 6502 jump to the wrong address.) This bug and others were fixed in the CMOS version.

I will point point out that the note on clock cycle times is still wrong. I have tried to get the author to change this, but have gotten no response. When an instruction takes two cycles (like ORA #40H), it will take one microsecond at 2MHz-- two clock pulses, not four.

Western Design Center sells by far the best programming manual I know of, called "Programming the 65816, Including the 6502, 65C02, and 65802", by David Eyes and Ron Lichty. At somewhere around $60, it's not cheap; but it's very, very thorough and clear. It really removes the mysteries. If you're serious about programming this family of processors, it's worth the money. If you want to program specifically the 65816 (a 6502 with 16-bit registers and a much more powerful instruction set), you cannot afford to be without this book.

Garth

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http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

Tony

I am greatful for your words of wisdom and as the weeks go by I am slowly picking things up. Perhaps my most important requirement at the moment is some means of simulation when I write my program. In the college I attend we have an EMMA simulator, which we can program and when in the run mode it will "behave " in the appropriate manner ( unless I program it in which case it doesn't do what I thought I had asked it to do!). If there was some sort of DOS or Windows aid I could turn to I would be happy, Once again I welcome any suggestions, comments.
Regards

Ronnie

Ronnie,

I have a 65C02 simulator written for windows 95/98 that might help.
If you are interested, it can be downloaded free from my web site:

Also, there are links to a couple other simulators on the 6502.org web site.

Daryl

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Please visit my website -> https://sbc.rictor.org/