Verilog, testing for Zero flag

Question

module NOR31_1x1(Y,A);
input [31:0] A;
output Y;

wire [29:0] norWire;

    nor nor1(norWire[0], A[0], A[1]);
        nor nor2(norWire[1], norWire[0], A[2]);
    nor nor3(norWire[2], norWire[1], A[3]);
    nor nor4(norWire[3], norWire[2], A[4]);
    nor nor5(norWire[4], norWire[3], A[5]);
    nor nor6(norWire[5], norWire[4], A[6]);
    nor nor7(norWire[6], norWire[5], A[7]);
    nor nor8(norWire[7], norWire[6], A[8]);
    nor nor9(norWire[8], norWire[7], A[9]);
    nor nor10(norWire[9], norWire[8], A[10]);
    nor nor11(norWire[10], norWire[9], A[11]);
    nor nor12(norWire[11], norWire[10], A[12]);
    nor nor13(norWire[12], norWire[11], A[13]);
    nor nor14(norWire[13], norWire[12], A[14]);
    nor nor15(norWire[14], norWire[13], A[15]);
    nor nor16(norWire[15], norWire[14], A[16]);
    nor nor17(norWire[16], norWire[15], A[17]);
    nor nor18(norWire[17], norWire[16], A[18]);
    nor nor19(norWire[18], norWire[17], A[19]);
    nor nor20(norWire[19], norWire[18], A[20]);
    nor nor21(norWire[20], norWire[19], A[21]);
    nor nor22(norWire[21], norWire[20], A[22]);
    nor nor23(norWire[22], norWire[21], A[23]);
    nor nor24(norWire[23], norWire[22], A[24]);
    nor nor25(norWire[24], norWire[23], A[25]);
    nor nor26(norWire[25], norWire[24], A[26]);
    nor nor27(norWire[26], norWire[25], A[27]);
    nor nor28(norWire[27], norWire[26], A[28]);
    nor nor29(norWire[28], norWire[27], A[29]);
    nor nor30(norWire[29], norWire[28], A[30]); 
        nor result(Y, norWire[29], A[31]);
endmodule

Hi, so I wrote the code above to test if Zero flag is set by nor each bit against another, It seems that the logic is correct, but the result keeps return 1 for zero flag regardless of any input. I ran through the simulation to test and it seems that norWire already contain some value despite not being set any value yet. Can I get some help debugging this please. I'm having a hard time debugging this due to being new to Verilog and the ModelSim simulator.

Answer 1

Let's limit this to three bits to illustrate the problem. If we label the bits A, B, and C what you're trying to express is:

!(A | B | C)

What you've written is:

!(!(A | B) | C)

where the output of one NOR (complete with the final negation) is being fed forward to the next stage.

So some judicious use of 'or' and 'not' primatives should get you there.