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// This model is the property of Cypress Semiconductor Corp and is protected 
 
// by the US copyright laws, any unauthorized copying and distribution is prohibited.
 
// Cypress reserves the right to change any of the functional specifications without
 
// any prior notice.
 
// Cypress is not liable for any damages which may result from the use of this 
 
// functional model.
 
//This model checks for all the timimg violations and if any timing specifications 
//are violated,the output might be undefined or go to a high impedance state while 
//reading.Please note that the variable "tsim" in this model has to be changed as 
//per your convenience for the simulation time.
 
//      Model:       512Kx8
 
 
//      Contact:     mpd_apps@cypress.com   
 
//******************************************************************************
`timescale 1 ns/1 ps
 
 
module A512Kx8(Address,dataIO ,OE_bar,CE_bar,WE_bar);
 
`define tsim  30000
 
 
 
input [18:0] Address;
inout [7:0]  dataIO ;
input OE_bar,CE_bar,WE_bar;
reg   [7:0] temp_array [524287:0];
reg   [7:0] mem_array [524287:0];
reg   [7:0] data_temp;
reg   [18:0] Address1,Address2,Address3,Address4 ;
reg   [7:0] dataIO1;
reg   ini_cebar,ini_webar,ini_wecebar;
reg   initiate_write1,initiate_write2,initiate_write3;
reg   initiate_read1,initiate_read2; 
reg   delayed_WE;
 
integer fsram1;
 
time twc ;
time tpwe;
time tsce;
time tsd ;
time trc;
time thzwe;
time tdoe;
 
 
time write_address1,write_data1,write_CE_bar_start1,write_WE_bar_start1; 
time write_CE_bar_start,write_WE_bar_start,write_address,write_data;
time read_address,read_CE_bar_start,read_WE_bar_start;
 
initial
  begin
    initiate_write1 = 1'b0;
    initiate_write2 = 1'b0;
    initiate_write3 = 1'b0;
    initiate_read1 =1'b0;
    initiate_read2 =1'b0;
    read_address =0;  
    twc =10 ;
    tpwe =7;
    tsce =7 ;
    tsd = 5 ;
    trc =10 ;
    thzwe = 5;
    tdoe = 5;
//    fsram1 = $fopen("sram1.log");
 
  end
 
// Added thzwe for WE_bar going low
 
wire [7:0] dataIO =  (!OE_bar && delayed_WE) ?  data_temp[7:0] : 8'bz ;
 
always@(CE_bar or WE_bar or OE_bar or Address or dataIO )
 begin
 
	if ((CE_bar==1'b0) && (WE_bar ==1'b0))
           begin
              Address1 <= Address;
              Address2 <= Address1;
              dataIO1  <= dataIO;  
 	      temp_array[Address1] <=  dataIO1[7:0] ;
           end
 end
 
always@(negedge CE_bar)
   begin
     write_CE_bar_start <= $time;
     read_CE_bar_start <=$time;
     ini_cebar <= 1'b0;
     ini_wecebar<=1'b0;
   end
 
//*******************Write_cycle**********************
 
always@(posedge CE_bar)
   begin
      if (($time - write_CE_bar_start) >= tsce)
         begin
            if ( (WE_bar == 1'b0) && ( ($time - write_WE_bar_start) >=tpwe) )
              begin
               Address2 <= Address1;
               temp_array[Address1] <= dataIO1[7:0];  
                ini_cebar <= 1'b1;
              end
            else
               ini_cebar <= 1'b0;
         end            
      else
         begin 
           ini_cebar <= 1'b0;
         end
   end
 
always@(negedge WE_bar)
   begin
      write_WE_bar_start <= $time;
      ini_webar <= 1'b0;
      ini_wecebar<=1'b0;
#thzwe delayed_WE <= WE_bar;
 
   end
 
always@(posedge WE_bar  )
   begin
      delayed_WE <= WE_bar;
      read_WE_bar_start <=$time;
      if (($time - write_WE_bar_start) >=tpwe)
         begin
            if ( (CE_bar == 1'b0) && ( ($time - write_CE_bar_start) >= tsce) )
              begin
               Address2 <= Address1;   
               temp_array[Address1] <= dataIO1[7:0]; 
               ini_webar <= 1'b1;
              end 
            else 
               ini_webar <= 1'b0;
         end       
      else
         begin
           ini_webar <= 1'b0;
         end 
end    
 
always@(CE_bar && WE_bar)
   begin
     if ( (CE_bar ==1'b1) && (WE_bar ==1'b1) )
        begin 
           if ( ( ($time - write_WE_bar_start) >=tpwe) && (($time-write_CE_bar_start) >=tsce))
             ini_wecebar <=1'b1;
           else
             ini_wecebar <= 1'b0 ;    
        end 
     else
        ini_wecebar <=1'b0;
   end
 
always@(dataIO)
  begin
     write_data <= $time;
     write_data1 <=write_data;
     write_WE_bar_start1 <=$time;
     write_CE_bar_start1 <=$time;
     if ( ($time - write_data) >= tsd)
       begin
         if ( (WE_bar == 1'b0) && (CE_bar == 1'b0))
           begin
             if ( ( ($time - write_CE_bar_start) >=tsce) && ( ($time - write_WE_bar_start) >=tpwe) && (($time - write_address) >=twc) )
                initiate_write2 <= 1'b1;
             else
                initiate_write2 <= 1'b0;
           end
       end
  end
 
always@(Address)
  begin
     write_address <= $time;
     write_address1 <= write_address;
     write_WE_bar_start1 <=$time;
     write_CE_bar_start1 <=$time;
     if ( ($time - write_address) >= twc)
       begin
         if ( (WE_bar == 1'b0) &&  (CE_bar ==1'b0))
           begin
             if ( ( ($time - write_CE_bar_start) >=tsce) && ( ($time - write_WE_bar_start) >=tpwe) && (($time - write_data) >=tsd) )
                initiate_write3 <= 1'b1;
             else
                initiate_write3 <= 1'b0;
           end
         else
            initiate_write3 <= 1'b0;
       end
     else
        initiate_write3 <= 1'b0;
  end
 
always@(ini_cebar or ini_webar or ini_wecebar) 
  begin
     if ( (ini_cebar == 1'b1) || (ini_webar == 1'b1) || (ini_wecebar == 1'b1) ) 
       begin
         if ( ( ($time - write_data1) >= tsd) && ( ($time - write_address1) >= twc) )
            initiate_write1 <= 1'b1;
         else
            initiate_write1 <= 1'b0;
       end
     else
       initiate_write1 <= 1'b0;
  end 
 
//Removed address change completing a write
//removed initiate_write3
//always@(initiate_write2 or initiate_write3)   
 
always @(initiate_write2)  
  begin
     if ( (initiate_write2==1'b1) || (initiate_write3==1'b1)) 
         begin         
            if ( ( ($time - write_WE_bar_start) >=tpwe) && ( ($time - write_CE_bar_start) >=tsce))
	      begin		                                                            
//		 $fdisplay(fsram1, "%t initiate_write2 [%h] <- %h", $time, Address2, temp_array[Address2]);
                  mem_array[Address2] <= temp_array[Address2];
              end
         end
      initiate_write2 <=1'b0;
      initiate_write3 <=1'b0;
  end  
 
always@( initiate_write1 )   
  begin
     if (initiate_write1==1'b1)   
         begin         
            if ( ( ($time - write_WE_bar_start) >=tpwe) && ( ($time - write_CE_bar_start) >=tsce)) begin
//&& (($time - write_WE_bar_start1) >=tpwe) && (($time - write_CE_bar_start1) >=tsce))     
//	       $fdisplay(fsram1, "%t initiate_write1 [%h] <- %h", $time, Address2, temp_array[Address2]);
               mem_array[Address2] <= temp_array[Address2];               
	    end
         end
      initiate_write1 <=1'b0;
   end    
 
//*********************Read_cycle******************
 
always@(Address)
   begin 
     read_address <=$time;
     Address3 <=Address;
     Address4 <=Address3;
     if ( ($time - read_address) == trc) 
       begin
         if ( (CE_bar == 1'b0) && (WE_bar == 1'b1) )
           initiate_read1 <= 1'b1;
         else
           initiate_read1 <= 1'b0;
       end  
     else
       initiate_read1 <= 1'b0;
   end
 
always
  #1
  begin 
     if ( ($time - read_address) >= trc)
       begin
         if ( (CE_bar == 1'b0) && (WE_bar == 1'b1) )
           begin
             Address4 <=Address3;
             initiate_read2 <= 1'b1;
           end
         else
             initiate_read2 <= 1'b0;
       end
     else
       initiate_read2 <= 1'b0;
   end
// initial # `tsim $finish;    
 
always@(initiate_read1 or initiate_read2)
   begin
     if ( (initiate_read1 == 1'b1) || (initiate_read2 == 1'b1) )
       begin
         if ( (CE_bar == 1'b0) && (WE_bar ==1'b1) )
           begin
             if ( ( ($time - read_WE_bar_start) >=trc) && ( ($time -read_CE_bar_start) >=trc) ) begin
//	       $fdisplay(fsram1, "%t initiate_read1/2 [%h] -> %h", $time, Address4, mem_array[Address4]);
               data_temp[7:0] <= mem_array[Address4];
	     end
           end
         else
           #thzwe data_temp <=8'bzz;
       end
        initiate_read1 <=1'b0;
        initiate_read2 <=1'b0;
   end
 
always @(Address)
 begin
   if (CE_bar == 1'b0 && WE_bar == 1'b1 && OE_bar == 1'b0) begin
        #tdoe data_temp[7:0] <= mem_array[Address];
//        $fdisplay(fsram1, "%m %t Address [%h] -> %h", $time, Address, mem_array[Address]);
   end
 end
 
always @(WE_bar or OE_bar or  CE_bar)
 begin
   if (CE_bar == 1'b0 && WE_bar == 1'b1 && OE_bar == 1'b0) begin
//        $fdisplay(fsram1, "%t WE_bar/OE_bar/CE_bar [%h] -> %h", $time, Address3, mem_array[Address3]);       
         #tdoe data_temp[7:0] <= mem_array[Address3];
   end
 end
 
 
endmodule