PC register can be specified as "PC" or "pc", but "Pc" and "pC" forms are not
allowed.
An and Dn register can be specified with capital or small letter no problem.

"-" - Expression or -(An)
"-(" - Expression or -(An)
"--" - Expression
"-(a1" - -(An), only ')' expected further
"-(a1)" - -(An), done

"#" - Immediate expression, no registers allowed, no size specifiers allowed

"(" - Addr Expression, (An), (An)+, (d16,An), (d16,pc), (d8,An,Xi) or (d8,pc,Xi)
"(a1" - (An), (An)+, (d16,An) or (d8,An,Xi)
"(a1," - (An), (An)+, (d16,An) or (d8,An,Xi)
"(d1" - (d8,An,Xi) or (d8,pc,Xi)
"(d1," - (d8,An,Xi) or (d8,pc,Xi)
"(pc" - (d16,pc) or (d8,pc,Xi)
"(a1)" - (An), (An)+
"(a1)+" - (An)+, done