//	Dean Brock -- April, 1997
//
// This is a Example 1 of a combintorial circuit
//
// Here is the combinational circuit that was used to drive
// the J-K flipflops in the implementation of the nabs machine.
//
// See http://www.cs.unca.edu/~brock/classes/Spring97/274/sequen.html
// for more information about the sequential machine that contains
// this combinational circuit.

// Here the combinational circuit is specified as a dataflow model
// in which output are specified in a C-like syntax.
module comboCircuit(z, jA, kA, jB, kB, x, y, A, B) ;

output z, jA, kA, jB, kB ;
input  x, y, A, B ;

  assign  z = x&y&A&B ;
  assign jA = ~x&y&~A&B | x&~y ;
  assign jB = ~x&y | x&~y&A ;
  assign kA = x&y&A&B ;
  assign kB = ~x&y&~A&B | x&y&A&B ;
endmodule

// This is the module stimulus

module simulate ;

reg inX, inY, inA, inB ;
wire outZ, outJA, outKA, outJB, outKB ;

// Here as an instantiation of the combinational circuit.
  comboCircuit C(outZ, outJA, outKA, outJB, outKB, inX, inY, inA, inB) ;

// This is testing funcion.
// It is setting new inputs to the circuit at time
// units 3, 8, 13, 18, ....
// The #3 and #5 statements are time delays
initial
begin
  #3 ;
  {inX, inY, inA, inB } = 4'b0000 ;
  #5 ;
  {inX, inY, inA, inB } = 4'b0001;
  #5 ;
  {inX, inY, inA, inB } = 4'b0010;
  #5 ;
  {inX, inY, inA, inB } = 4'b0011;
  #5 ;
  {inX, inY, inA, inB } = 4'b0100;
  #5 ;
  {inX, inY, inA, inB } = 4'b0101;
  #5 ;
  {inX, inY, inA, inB } = 4'b0110;
  #5 ;
  {inX, inY, inA, inB } = 4'b0111;
  #5 ;
  {inX, inY, inA, inB } = 4'b1000;
  #5 ;
  {inX, inY, inA, inB } = 4'b1001;
  #5 ;
  {inX, inY, inA, inB } = 4'b1010;
  #5 ;
  {inX, inY, inA, inB } = 4'b1011;
  #5 ;
  {inX, inY, inA, inB } = 4'b1100;
  #5 ;
  {inX, inY, inA, inB } = 4'b1101;
  #5 ;
  {inX, inY, inA, inB } = 4'b1110;
  #5 ;
  {inX, inY, inA, inB } = 4'b1111;
  #5 ;
  $finish ;
end

// This loop is the output generation side of the testing unit.
// At time units 5, 10, 15, .... it prints the input and output
// values of the function.
initial
begin
  $display("") ;
  $display("Example 01") ;
  $display("") ;
  forever
  begin
    #5 ;
    $display("(%b,%b,%b,%b) -> %b,%b,%b,%b,%b",
	     inX, inY, inA, inB, outZ, outJA, outKA, outJB, outKB) ;

  end
end


endmodule