In this scheme, look up table of {TAIL ~ Φv1} or Φv2 is selected based on the output from {HEAD ~ the logical OR gate} by feeding this output to the chip selection pin of the ROM chips 
In this scheme , look up table of { TAIL ~ Φv1 } or Φv2 is selected based on the output from { HEAD ~ the logical OR gate } by feeding this output to the chip selection pin of the ROM chips
OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH