1. m4_1e - a multiplexer with inputs in[3:0], sel[1:0], e and output o. The output o is 0 when e=0 and when e=1 it is in[N] where N is the number corresponding to the binary value of sel[1:0].

2. m8_1e - a multiplexer with inputs in[7:0], sel[2:0], e and output o. The output o is 0 when e=0 and when e=1 it is in[N] where N is the number corresponding to the binary value of sel[2:0].

3. m2_1x8 - a multiplexer with inputs in0[7:0], in1[7:0], sel and output o[7:0]. The output o[7:0] is in0[7:0] if sel=0 and in1[7:0] when sel=1.

4. The inputs to the AddSub8 are the two 8-bit two's complement numbers, A[7:0] and B[7:0], and the input sub. When sub =0, the output, S[7:0] should be the sum of the two numbers, A+B, in two's complement. When sub =1, the output is A-B in two's complement.