B2 Bo Ao PFA PFA PFA G P C Ge Po ············ ···中···········可··············引············上· PPPP Go-3=G3+PG2+PPG+PPPGo 自学书页P139-140,加法器扩展。P0－3 ＝P3 P2 P1 P0 G0－3 = G3 + P3G2 + P3 P2G1 + P3 P2 P1G0 自学书页 P139－140，加法器扩展。 S G P B A C PFA PFA PFA PFA C0 B3 A3 B2 A2 B1 A1 B0 A0 G3 P3 C3 S2 C2 S1 G1 P1 S G0 G2 P2 C1 0 C4 S3 P0 G0－3 P0－3