Z-80 OpCode Formation Rules: 
 
Introductory note -- Binary form of opcodes
   
  Example:   LD r,r'
 
the 8-bit binary opcode is
 
     01dddsss
 
   ...where "ddd" is a three-bit field specifying the destination,
  and "sss" is a three-bit field specifying the source.
 
is shown below as
                          r   r'
                      01 xxx xxx
 
 
Detailed info LD
 
Instruction Format:
 
OPCODE  r    r'                             CYCLES
----------------------------------------------------
  01   XXX  XXX     LD   r,r'    dst,src      4
 
 
Register  r,r'
--------------
 A = 111
 B = 000
 C = 001
 D = 010
 E = 011
 H = 100
 L = 101
 
 

read more about this in the z80syntx.htm

    Source: geocities.com/siliconvalley/peaks/3938

               ( geocities.com/siliconvalley/peaks)                   ( geocities.com/siliconvalley)