Sx instruction decision tree

The image below shows a decision tree that can be used by an SX instruction decoder. Such a decoder could examine the bits of an instruction word from most significant (left) to least significant (right), starting at the root of the tree. Depending on the bit value found, the decoder takes either the '1' or the '0' branch. When the decoder reaches a labeled node, we have decoded enough bits to identify the instruction. Example: when the encoder finds the bit values 0, 1, 0, 1, we've identified the 'setb_fr_bit' (SETB <fr>.<bit>) instruction.