cntreg.v

vcs tutorial lab1

module CNTREG(D,MODE,SEL,RD_,WR_,CLK,COUNTLSB,COUNTMSB,MODEWRITE,LOAD,OUTEN);

  input        SEL,
               RD_,
               WR_,
               CLK,
               MODEWRITE;

  input  [5:1] MODE;
  input  [7:0] D;

  output       LOAD,
               OUTEN;

  output [7:0] COUNTLSB,
               COUNTMSB;

  reg          LOAD,
               OUTEN,
               LOADLSB,
               SETLOADLSB,
               CLRLOADLSB;
 
  reg    [7:0] COUNTLSB,
               COUNTMSB;
 
  // Count Register

  always @(posedge WR_)
    if (SEL & RD_)
      case (MODE[5:4])
        'b01 : begin

                 // Write LSB

                 COUNTLSB = D;

                 // Load Count On Next Rising CLK In Modes 0, 2, 3 and 4

                 if ((MODE[3:1] != 1) || (MODE[3:1] != 5))
                   LOAD = 'b1;

                 // Enable Output

                 OUTEN = 'b1;

               end
        'b10 : begin

                 // Write MSB

                 COUNTMSB = D;

                 // Load Count On Next Rising CLK In Modes 0, 2, 3 and 4

                 if ((MODE[3:1] != 1) || (MODE[3:1] != 5))
                   LOAD = 'b1;

                 // Enable Output

                 OUTEN = 'b1;

               end
        'b11 : if (LOADLSB)
                 begin
                   
                   // Write LSB First
 
                   COUNTLSB = D;
                   CLRLOADLSB = 'b1;
 
                 end
               else
                 begin

                   // Write MSB Only After LSB Loaded

                   COUNTMSB = D;
                   SETLOADLSB = 'b1;

                   // Load Count On Next Rising CLK In Modes 0, 2, 3 and 4

                   if ((MODE[3:1] != 1) || (MODE[3:1] != 5))
                     LOAD = 'b1;

                   // Enable Output

                   OUTEN = 'b1;

                 end
      endcase

  always @(posedge CLK)
    LOAD = 'b0;

  // Flag LOADLSB Is Set When In 2 Byte Mode And LSB Has Not Been Read Yet

  always @(SETLOADLSB or MODEWRITE)
    if (SETLOADLSB || MODEWRITE)
      begin
        OUTEN = 'b0;
        LOADLSB = 'b1;
        COUNTLSB = 8'b0;
        COUNTMSB = 8'b0;
      end

  // Flag LOADLSB Is Cleared When In 2 Byte Mode And LSB Has Been Read

  always @(CLRLOADLSB)
    if (CLRLOADLSB)
      LOADLSB = 'b0;

endmodule