This table lists the legal source/destination combinations for the LD instruction. Thanks to John Powers for looking this up so we don't have to.

LD <dest> <source>

X marks a legal source/dest combination

         Source
Dest   imm mem A B C D E H L (BC) (DE) (HL) (IX) (IY) BC DE HL IX IY SP
      ------------------------------------------------------------------
mem  |  .   .  X . . . . . .  .    .    .    .    .   X  X  X  X  X  X
     | 
A    |  X   X  . X X X X X X  X    X    X    X    X   .  .  .  .  .  .
B    |  X   .  X . X X X X X  .    .    X    X    X   .  .  .  .  .  .
C    |  X   .  X X . X X X X  .    .    X    X    X   .  .  .  .  .  .
D    |  X   .  X X X . X X X  .    .    X    X    X   .  .  .  .  .  .
E    |  X   .  X X X X . X X  .    .    X    X    X   .  .  .  .  .  .
H    |  X   .  X X X X X . X  .    .    X    X    X   .  .  .  .  .  .
L    |  X   .  X X X X X X .  .    .    X    X    X   .  .  .  .  .  .
     | 
(BC) |  .   .  X . . . . . .  .    .    .    .    .   .  .  .  .  .  .
(DE) |  .   .  X . . . . . .  .    .    .    .    .   .  .  .  .  .  .
(HL) |  X   .  X X X X X X X  .    .    .    .    .   .  .  .  .  .  .
(IX) |  X   .  X X X X X X X  .    .    .    .    .   .  .  .  .  .  .
(IY) |  X   .  X X X X X X X  .    .    .    .    .   .  .  .  .  .  .
     | 
BC   |  X   X  . . . . . . .  .    .    .    .    .   .  .  .  .  .  .
DE   |  X   X  . . . . . . .  .    .    .    .    .   .  .  .  .  .  .
HL   |  X   X  . . . . . . .  .    .    .    .    .   .  .  .  .  .  .
IX   |  X   X  . . . . . . .  .    .    .    .    .   .  .  .  .  .  .
IY   |  X   X  . . . . . . .  .    .    .    .    .   .  .  .  .  .  .
     | 
SP   |  X   X  . . . . . . .  .    .    .    .    .   .  .  X  X  X  .

imm  = immediate data such as $80DF
mem  = memory address such as ($80DF)
(BC) = using the value in BC as a memory address