ENTITY counter_4 IS PORT(
    clock, reset, load_counter: IN BIT;
    data:                       IN BIT_VECTOR( 3 DOWNTO 0 );
--
-- BUFFER means that we can reference the value of this signal from 
-- inside the architecture.
--
    reset_alert:                OUT BIT;
    count:                      BUFFER BIT_VECTOR( 3 DOWNTO 0 ) 
    );
END counter_4;

ARCHITECTURE behavioral OF counter_4 IS
BEGIN
--
-- The process only starts when there is a change to one of the signals in
-- its sensitivity list.
--
    upcount: PROCESS( clock ) BEGIN
--
-- You can only use an IF statement if you are inside of a PROCESS.  Here,
-- the IF statement tests for the rising clock edge.
--
        IF( clock'event AND clock= '1' ) THEN
            IF reset = '1' THEN
                count <= "0000";
            ELSIF load_counter = '1' THEN
                count <= data;
            ELSE
                count(0) <= NOT count(0);
                count(1) <= count(0) XOR count(1);
                count(2) <= ( count(0) AND count(1) ) XOR count(2);
                count(3) <= ( count(0) AND count(1) AND count(2) ) XOR count(3);
                IF count = "0000" THEN 
                    reset_alert <= '1';
                ELSE
                    reset_alert <= '0';
                END IF; -- IF count = "0000"
            END IF; -- IF load = '1'
        END IF; -- IF( clock'event AND clock = '1' )
    END PROCESS upcount;
END behavioral;