I have to rewrite the assembler and disassembler... so here is the census of the instructions and their syntax, in order of complexity :-)

• NOP => 0000h
  INV,
  HLT => FFFFh
• OVL  Imm8 => FF........h
• IN,
  OUT SND Imm8 => (no SRI)  Ch snd i/o Imm8
• LDCL,
  LDCH  SND SRI => (no Imm8) Dh snd l/h ..... sri  (condition not supported yet)
  
• XOR,
  OR,
  AND,
  ANDN,
  CMPU,
  CMPS,
  SUB,
  ADD,
  SHR,
  SHL,
  SAR,
  ROL,
  SET,
  CALL SND  Imm8/Imm4 [cond2]/SRI [cond3] => (see diagram)

This should help structure the code :-) There are 4 special cases to check, and then it's all very orthogonal.