module
KeyPadEncoder

// Encodes the ten keypad lines into a four-bit binary value.
// NOTES:
// 1. Higher digits have higher priority on multiple keypress
// 2. 'KeyValue' should not be used unless 'KeyIsPressed' is asserted

(
// Data inputs:
iD$KeyPad,			// Keypad lines (10-bit bus)

// Condition signals to controller:
oS$KeyIsPressed,	// Asserted when any key is pressed

// Data outputs:
oD$KeyValue			// Value of key that is pressed; only valid
						// when KeyIsPressed is asserted.
);

input		[9:0]	iD$KeyPad;
output	oS$KeyIsPressed;
output	[3:0]	oD$KeyValue;

reg	oS$KeyIsPressed;
reg	[3:0]	oD$KeyValue;

always @ (iD$KeyPad) begin
	casez (iD$KeyPad)
   	10'b1????????? : oD$KeyValue <= 4'd9;
   	10'b01???????? : oD$KeyValue <= 4'd8;
   	10'b001??????? : oD$KeyValue <= 4'd7;
   	10'b0001?????? : oD$KeyValue <= 4'd6;
   	10'b00001????? : oD$KeyValue <= 4'd5;
   	10'b000001???? : oD$KeyValue <= 4'd4;
   	10'b0000001??? : oD$KeyValue <= 4'd3;
   	10'b00000001?? : oD$KeyValue <= 4'd2;
   	10'b000000001? : oD$KeyValue <= 4'd1;
   	10'b0000000001 : oD$KeyValue <= 4'd0;
		default : oD$KeyValue <= 4'd0;
	endcase

	oS$KeyIsPressed <= iD$KeyPad != 0;
end

endmodule