Friday, October 7, 2011

pSRAM memory test for the Nexys 2

This is a very simple pSRAM memory test for the Nexys 2 with the Spartan 3E 500 FPGA. Simply writes and reads back the memory.

Note that the RAM chip on the Nexys 2 board is the MT45W8MW16BGX in a BGA package.

module Main(
 input wire clk,
 output wire [7:0] Led,
 input wire [3:0] btn,
 output wire MemOE,
 output wire MemWR,
 output wire RamAdv,
 output wire RamCS,
 output wire RamClk,
 output wire RamLB,
 output wire RamUB,
 output wire [23:1] MemAdr,
 inout wire [15:0] MemDB

reg [31:0] state = 0;
reg [7:0] rLed;

reg rMemOE = 1;
reg rMemWR = 1;
reg [15:0] rMemDB;
reg [23:1] rMemAdr;

//Static assignments
assign RamCS = 0; //chip select is always low (enabled)
assign RamClk = 0; //clk is disabled in asynchronous mode
assign RamAdv = 0; //address valid can always be pulled low in asynchronous mode
assign RamLB = 0; //lower byte is enabled
assign RamUB = 0; //upper byte is enabled

//Register assignments
assign MemOE = rMemOE;
assign MemWR = rMemWR;
assign MemDB[15:0] = rMemDB[15:0];
assign MemAdr[23:1] = rMemAdr[23:1];

assign Led[7:0] = rLed[7:0];

always @(posedge clk)
 if(btn[0])      //btn[0] is reset/write
  state <= 0;
 else if(btn[1])    //btn[1] is read
  state <= 50;
 else if(btn[2])    //btn[2] just toggles Led[7]
  rLed[7] <= ~rLed[7]; 
 else begin
   0: begin
    rMemAdr <= 23'b0;  //set address to 0
    rMemDB <= 16'h0505;  //write 0x0505 to the data bus
    rMemWR <= 0;   //pull write enable low to write the data
    state <= 10;
   10: begin
    rMemWR <= 1;   //pull write enable to high again
   50: begin
    rMemDB <= 16'bzzzzzzzzzzzzzzzz;  //set the data bus to high impedance
    rMemOE <= 0;      //pull output enable low to start a read
    state <= 60;
   60: begin
    rLed[3:0] <= MemDB[7:0];   //set the LEDs to show the data
    state <= 70;
   70: begin
    rMemOE <= 1;      //pull output enable high again



  1. The logic does work, although I had to take out the pushbutton controll, since it did not synthesize in Xilinx ISE. Thx for sharing!

  2. Thanks for this example! It helps me alot.