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The use of the case statement

The use of the case statement


I am trying to write a verilog code for simple CPU for one of my assignmnets. The following is the program I have written so far but found that the prgram is not going in to the case statement at all. Can someone help me figure out the mistake please?

Thanks very much.

module cpu(clock, run, mbr_out);
    input clock;
    input run;
    output[7:0] mbr_out;
reg [7:0] pc, ir, mar,mbr ,mbr_r, dreg, mbr_out;
reg fetch, decode, mem_write, ce, ld, ad, sub, store;
wire clock, run;
wire [7:0] mbr_in;

main_mem mm1 (.clock(clock),.add_in(mar),.data_out(mbr_in),.data_in(mbr_out),.rd_wr

(mem_write) );


always@ (posedge clock, ld, ad, sub, store, fetch, decode)

if (run)


case ({clock,ld, ad, sub, store, fetch, decode})
     mbr = mbr_in;
     dreg [3:0] = mbr [3:0];
     ld =0;
    mbr = mbr_in;
    dreg[3:0] = dreg[3:0] + mbr[3:0];
    ad =0;
    mbr = mbr_in;
    dreg = dreg - mbr;
    sub =0;
    mbr = dreg;
    mbr_out = mbr;
    mem_write =1;
    store =0;
    mar =pc;
    mbr_r = mbr;
    decode =1;
    fetch =0;
    mbr = mbr_in;
    if (mbr_r== mbr)
      fetch = 1;
       ir[3:0] = mbr[7:4];
         mar[3:0] = mbr[3:0];
          casex (ir)
                 8'bxxxx0001 : ld =1;  // load
                8'bxxxx0010 : ad = 1; // add
                8'bxxxx0011 : sub =1;// subtract
                8'bxxxx0101 : store =1;// store
        decode =0;

module main_mem (clock, add_in, data_out, data_in, rd_wr, CE);

input [7:0]add_in, data_in;
input CE, clock, rd_wr;
output data_out;
wire [7:0] add_in, data_in;
reg [7:0] data_out;
reg[7:0] membyte[0:16];
wire rd_wr;

pc = 1;
mem_write =0;
mbr =0;
mar =0;
data_out =0;
mbr_out =0;
membyte[10] = 8'b 00000010; // data 10
membyte[11] = 8'b 00000011; // data 11
membyte[12] = 8'b 00000001;// data 12
membyte[0] =  8'b 00000000;
membyte[1] =  8'b 00011010; // load mem 10
membyte[2] =  8'b 00101011; // add mem 11
membyte[3] =  8'b 01011110; // store mem 14
//membyte[3] = 8'b 00001110; // load mem 14
//membyte[4] = 8'b 00101100; // subtract 12
//membyte[5] = 8'b 00111111; //store in 15


always@(posedge clock)
    membyte[add_in]= data_in;
    data_out = membyte[add_in];


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