/* ************************************************************ */
declare CNT4 {

    input       PARAM_in[4] ;   // Initial parameter．
    input       LOAD_in ;       // Synchronous PARAM_in load request.
    input       ENB_in ;        // Count enable
    func_in     CARRY_in() ;    // Carry-input from a lower level 4bit
                                // counter's carry-output.

    output      Q_out[4] ;      // Flip-Flop data output
    func_out    CARRY_out() ;   // Carry-output to a higher lovel 4bit
                                // counter's carry-input

}

/* ************************************************************ */
// Declare module
module CNT4 {

/* ************************************************************ */
// Internal operation signals
    reg         Counter_4bit[4] ;       // DタイプF/Fの宣言．

/* ************************************************************ */
// Equation

/* *********************************************** */
/* Pallarel equation */

    {
    /* **** Data output **** */
        Q_out = Counter_4bit ;      // Q_out = Counter_4bit[3:0] is OK.
                                    // Q_out[3:0] = .... is NG.

    /* **** Flip-Flop equation **** */
        if ( LOAD_in )
            Counter_4bit := PARAM_in ;

    /* **** Carry-out equation **** */
        if ( Counter_4bit == 4'b1111 ) {
            CARRY_out() ;
        }
    }

/* *********************************************** */
/* Function independent equation */
    function    CARRY_in {
        if ( ENB_in ) {
            Counter_4bit := Counter_4bit + 4'b1 ;
                            // Must define inclement data bit width !!!
        }
    }

}
/* ************************************************************ */