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// IS61LV25616 Asynchronous SRAM, 256K x 16 = 4M; speed: 10ns.

// Note; 1) Please include "+define+ OEb" in running script if you want to check

//          timing in the case of OE_ being set.

//       2) Please specify access time by defining tAC_10 or tAC_12.

// `define OEb

`define tAC_10

`timescale 1ns/10ps

module IS61LV25616 (A, IO, CE_, OE_, WE_, LB_, UB_);

parameter dqbits = 16;

parameter memdepth = 262143;

parameter addbits = 18;

parameter Toha  = 2;

parameter Tsa   = 2;

`ifdef tAC_10

  parameter Taa   = 10,

            Thzce = 3,

            Thzwe = 5;

`endif

`ifdef tAC_12

  parameter Taa   = 12,

            Thzce = 5,

            Thzwe = 6;

`endif

input CE_, OE_, WE_, LB_, UB_;

input [(addbits - 1) : 0] A;

inout [(dqbits - 1) : 0] IO;

wire [(dqbits - 1) : 0] dout;

reg  [(dqbits/2 - 1) : 0] bank0 [0 : memdepth];

reg  [(dqbits/2 - 1) : 0] bank1 [0 : memdepth];

// wire [(dqbits - 1) : 0] memprobe = {bank1[A], bank0[A]};

wire r_en = WE_ & (~CE_) & (~OE_);

wire w_en = (~WE_) & (~CE_) & ((~LB_) | (~UB_));

assign #(r_en ? Taa : Thzce) IO = r_en ? dout : 16'bz;

initial

  $timeformat (-9, 0.1, " ns", 10);

assign dout [(dqbits/2 - 1) : 0]        = LB_ ? 8'bz : bank0[A];

assign dout [(dqbits - 1) : (dqbits/2)] = UB_ ? 8'bz : bank1[A];

always @(A or w_en)

  begin

    #Tsa

    if (w_en)

      #Thzwe

      begin

        bank0[A] = LB_ ? bank0[A] : IO [(dqbits/2 - 1) : 0];

        bank1[A] = UB_ ? bank1[A] : IO [(dqbits - 1)   : (dqbits/2)];

      end

  end

// Timing Check

`ifdef tAC_10

  specify

    specparam

      tSA   = 0,

      tAW   = 8,

      tSCE  = 8,

      tSD   = 6,

      tPWE2 = 10,

      tPWE1 = 8,

      tPBW  = 8;

`else

`ifdef tAC_10

  specify

    specparam

      tSA   = 0,

      tAW   = 8,

      tSCE  = 8,

      tSD   = 6,

      tPWE2 = 12,

      tPWE1 = 8,

      tPBW  = 8;

`endif

`endif

    $setup (A, negedge CE_, tSA);

//     $setup (A, posedge CE_, tAW);

//     $setup (IO, posedge CE_, tSD);

    $setup (A, negedge WE_, tSA);

//     $setup (IO, posedge WE_, tSD);

    $setup (A, negedge LB_, tSA);

    $setup (A, negedge UB_, tSA);

    $width (negedge CE_, tSCE);

    $width (negedge LB_, tPBW);

    $width (negedge UB_, tPBW);

    `ifdef OEb

    $width (negedge WE_, tPWE1);

    `else

    $width (negedge WE_, tPWE2);

    `endif

  endspecify

endmodule