NEG - Negate (Two's Complement) ;flags(N,Z,C)
NEG opr ;(opr) < $00 - (opr) ;(DIR) 8 bit direct
NEG ,X ;(X) < $00 - (X) ;(IX) indexed no offset
NEG opr,X ;(opr+X) < $00 -(opr+X) ;(IX1) indexed,8 bit offset
Replaces the contents of M(opr) with its two's complement. Note that the value
$80 is left unchanged.