About 20 years ago,
a student or three asked for a 6502 opcode chart which showed the bit fields of each instruction. I do not believe they received a satisfactory response. I also believe that it remains beneficial to provide an alternative answer.
I like the format of datasheets in which 8 bit opcodes are typically shown within 16×16 grid, like an extended ASCII chart. Such a periodic table of the opcodes concisely explains rare Technetium (Terbium?) as the store immediate addressing mode. Such exceptions may be obscured in a bit field chart. However, for a student or experienced designer, familiar with larger instruction sets, a description of bit fields has become the norm, if it is explained at all. Therefore, we gain advocates away from from processors with a larger instruction-space by providing an at-a-glance comparison in a format that the typical 6502 advocate may find needlessly complicated.
Independent of
http://axis.llx.com/~nparker/a2/opcodes.html, I attempted to draw a chart in the style of Lance A. Leventhal's MC68000 guide. The result can be printed on one sheet if five point text is bearable. Although this may seem ludicrous, the equivalent for 68000 fills a large proportion of a 300 page book. The initial attempt took about two hours to draw. The current draft took about three days and I had to stop due to tendonitis. I have attempted to show the symmetry between the base and extended instructions across five dialects of 6502 without requiring blocks of color. Titling could probably be improved. I have also left deliberate errors in the draft. Therefore, if you don't find any errors then you are definitely wrong.
In a similar manner to my seven column multiplexed bus state machine diagram, the seven columns of the 6502 opcode bit field chart can be abridged for smaller systems. However, in both cases, it would be strongly preferable if abridged documentation is not widely circulated. Hopefully, this will be sufficient to prevent truncated versions displacing the full version.
I took the liberty of adding my own vaporware architecture extension and I found that it can be explained very concisely in this form. In the best interests of the whole 6502 community, I would be very happy to draft charts of other efforts in a similar manner. For example, the very regular instruction format of the source compatible 65m02 may be very concisely described in the style.
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