F617.v

/**************************************************************************
** ND120 DGA (Decode Gate Array)                                         **
** DECODE/DGA                                                            **
**                                                                       **
** NEC F617 - D Flip-Flop with RB, SB                                    **
**                                                                       **
** Truth table from REN_A12213XJ5V1UM00_OTH_19980801.pdf                 **
** Page 6-238. Function D-F/F WITH RB, SB                                **
**                                                                       **
** Last reviewed: 20-MAY-2024                                            **
** Ronny Hansen                                                          **
***************************************************************************/

module F617 (
    input H01_D,   // Data
    input H02_C,   // Clock 
    input H03_RB,  // Reset (negated)
    input H04_SB,  // Set (negated)

    output N01_Q,
    output N02_QB
);

  // Registers to hold outputs
  reg  regQ;
  reg  reqQ_n;

  // Wires
  wire s_sb;
  wire s_d;
  wire s_c;
  wire s_rb;


  // Assign inputs
  assign s_sb   = H04_SB;
  assign s_d    = H01_D;
  assign s_c    = H02_C;
  assign s_rb   = H03_RB;

  // Assign outputs
  assign N01_Q  = regQ;
  assign N02_QB = reqQ_n;


  always @(s_c, s_rb, s_sb) begin
    if (s_rb & s_sb) begin  // no forced clear or set
      regQ   <= s_d;
      reqQ_n <= ~s_d;
    end else if (s_sb & !s_rb) begin  // reset (negated SB)
      regQ   <= 1'b0;
      reqQ_n <= 1'b1;
    end else if (!s_sb & s_rb) begin  // set (negated RB  )
      regQ   <= 1'b1;
      reqQ_n <= 1'b0;
    end else begin  /* !s_rb & !s_sb */
      regQ   <= 1'b0;
      reqQ_n <= 1'b0;
    end

  end

endmodule


/* 

TRUTH TABLE
===========

| D | C       |RB | SB| Q | QB |
|---|---------|---|---|---|----|
| 0 | posedge | 1 | 1 | 0 | 1  |
| 1 | posedge | 1 | 1 | 1 | 0  |
| X | negedge | 1 | 1 |  Hold  |
| X |   X     | 0 | 1 | 0 | 1  |
| X |   X     | 1 | 0 | 1 | 0  |
| X |   X     | 0 | 0 | 0 | 0  |  <= prohibition

X=irrelevant

*/