/* File: DFlipFlop.java
 * Copy: Copyright (c) 1998 David Green
 * Vers: 1.0.0 1998/10/16 dgg -- derive from idea in OODemo2.cpp by
 *                               Dennis Smith
 */

/** Simulation of D flip flop
 *
 *  @author David Green
 *  @note   always set the d lead ahead of the clock lead when wiring
 */
public class DFlipFlop {
	// state of flip flop
	private boolean q;
	// present value of D input
	private boolean d;
	// present value of clock lead
	private boolean old_clock;

	/** default constructor */
	public DFlipFlop()
	{
		q = false;
		d = false;
		old_clock = false;
	}

	/** return flip flop state */
	public boolean getQ()
	{
		return q;
	}

	/** set the d value
	 *
	 *  @param new_d - new value of d input lead
	 *  @note this does not quite model wiring
	 */
	public void setD( boolean new_d )
	{
		d = new_d;
	}

	/** set clock
	 *
	 *  @param new_clock - new clock lead value
	 */
	public void setClock( boolean new_clock)
	{
		// if rising edge, clock D FF
		if ( (old_clock == false ) && (new_clock == true ) )
			q = d;

		old_clock = new_clock;
	}

	/** main - test driver */
	public static void main( String [] args )
	{
		DFlipFlop ff = new DFlipFlop();

		// initialize
		ff.setD( false );

		clockFF( ff );
		
		System.out.println("Test Program for D FF Simulation" );

		printFFState( ff );
		ff.setD( true );
		clockFF( ff );
		printFFState( ff );
	}

	// next methods are private methods for test driver only
	
    private static void clockFF( DFlipFlop ff )
	{
		ff.setClock( true );
		ff.setClock( false );
	}

	private static void printFFState( DFlipFlop ff )
	{
		System.out.println( "Flip-flop = " + ff.getQ() );
	}
}