Those reference cards are very helpful. In college the embedded PC boards (generic) x86 and (I forget if it was a 68 or 65 series CPU) each included a CPU manual and quick assembly reference card. Seeing instructions grouped by how the decoder wanted them, it was much easier to see where a given entry would have 3 or 4 bits utilized to decode a sub function among a general class of instructions.

Sadly I couldn't find a good link to a quick reference card, but there are some copies of the CPU manual on https://archive.org/search?query=6809 . A Wikipedia site is nowhere near as good as a properly typeset and slightly grouped to convey clarity card, but it's still useful https://github.com/Ta0uf19/Motorola-6809-Cheatsheet