设计了一个8位acc累加器，为什么无法从零开始累加呢？

8位全加器。add8.v
module add8(sum,cout,b,a,cin);
input[7:0] a/*synthesis keep*/,b/*synthesis keep*/;
input cin; output[7:0] sum/*synthesis keep*/;
output cout;
assign {cout,sum}=a+b+cin;
endmodule

8位寄存器。reg.v
module reg8(qout,in,clk,clear);
input[7:0] in/*synthesis keep*/;
input clk,clear;
output reg[7:0] qout/*synthesis keep*/;
always @ (posedge clk or posedge clear)
        begin
        if(clear)qout<=0;
        else qout<=in;
                        end
        endmodule

请问：设计出来的累加器只能从120开始累加，无法从零开始累加，就算是clear以后还是如此。要怎么把起始值设成零呢？
谢谢！~~