lcd_testbench.v

基于MAXII CPLD的对1602字符型液晶进行读写操作

/*****************************************************************************************************************
* TESTBENCH FOR LCD CONTROLER
* JANUARY 2007
*****************************************************************************************************************/

`timescale 1 us / 1 us

module lcd_testbench; 

reg rst,we;             // rst is active low asynchronous reset
                        // we is to be made 1 when writing data into lcd
reg [7:0] data;         // data lines from processor to LCD controller
reg [7:0] count;        // count is a register used to count the number of pulses on E

wire clk_w,ack,RW,RS,E;  
wire [7:0] DB;

/* Instantiation of the module under test */

lcd_controller lcd_final(.clk_w(clk_w),.rst(rst),.we(we),.ack(ack),.data(data),.DB(DB),.RW(RW),.RS(RS),.E(E));

initial 
begin
    rst = 0;                // Reset asserted
    we = 1;                 // Write enable disasserted
    data = 8'b00000000;     
    count = 8'b00000000;    // Count initialised to zero
end

always
begin
   #500
   rst =1;                     // Reset disasserted
   while(count <= 8'b00001001) // Loop to count the number of pulses on E and wait till 8 pulses have been generated
   begin
       @(negedge E)
       count = count + 8'b00000001;
   end
   $display("Initialisation Complete %d", $time); 
   count = 8'b00000000;       // Reinitialise count to zero

   @(negedge ack);            // Wait till acknowledge signal has been asserted

   $display("Default message has been displayed on LCD %d", $time);
  
   data = 8'b10011001;        // Data to be written into LCD
   we = 0;                    // Assert write enable

   @(negedge E);              // Wait for negative edge on E to latch data into LCD
   # 233
   $display("Since it is not possible to read busy flag in the testbench(due to absence of LCD), we are waiting for 233 us and assuming that in this time, busy flag would have gone low.Data has been written into LCD %d", $time);
    
   #500
   rst = 0;                    // Assert reset
   #500
   rst = 1;                    // Disassert reset
   while(count <= 8'b00001001) // Again wait for 8 negative edges on E
   begin
       @(negedge E)
       count = count + 8'b00000001;
   end

   $display("Initialisaton done again %d", $time);
   $display (" PASS: Checked for initialisation, display of the default message and the character whose ASCII equivalent is sent to the LCD %d", $time);  
   $stop;
   end
   
   endmodule

/***************************************** END OF TESTBENCH ****************************************************************************************************************************************************************************************/