User`s manual

299 //

300 // A shift register primitive is used to generate an active-high reset

301 // signal that remains high for 16 clock cycles after configuration finishes

302 // and the FPGA’s internal clocks begin toggling.

303 //

304 ////////////////////////////////////////////////////////////////////////////

305 wire reset;

306 SRL16 reset_sr(.D(1’b0), .CLK(clock_27mhz), .Q(reset),

307 .A0(1’b1), .A1(1’b1), .A2(1’b1), .A3(1’b1));

308 defparam reset_sr.INIT = 16’hFFFF;

309

310 ///////////////////////////////////////////////////////////////////////////////////////////////////

311 // create clocks

312 // use FPGA’s digital clock manager to produce a 50 MHz clock

313 // this clock is our system clock

314 // to drive VGA at 640x480 (60 Hz), we need a 25 MHz vga clock

315 // credits to Jose for computing the required clock values

316 // and use of ramclock module

317 ///////////////////////////////////////////////////////////////////////////////////////////////////

318 wire sys_clk_unbuf, sys_clk, vga_clk, vga_clk_unbuf;

319 wire slow_clk;

320 wire clk_locked;

321 DCM vclk1(.CLKIN(clock_27mhz),.CLKFX(sys_clk_unbuf));

322 // synthesis attribute CLKFX_DIVIDE of vclk1 is 15

323 // synthesis attribute CLKFX_MULTIPLY of vclk1 is 28

324 // synthesis attribute CLK_FEEDBACK of vclk1 is NONE

325 // synthesis attribute CLKIN_PERIOD of vclk1 is 37

326 BUFG vclk2(.O(sys_clk),.I(sys_clk_unbuf));

327 DCM int_dcm(.CLKIN(sys_clk), .CLKFX(vga_clk_unbuf), .LOCKED(clk_locked));

328 // synthesis attribute CLKFX_DIVIDE of int_dcm is 4

329 // synthesis attribute CLKFX_MULTIPLY of int_dcm is 2

330 // synthesis attribute CLK_FEEDBACK of int_dcm is NONE

331 // synthesis attribute CLKIN_PERIOD of int_dcm is 20

332 BUFG int_dcm2(.O(vga_clk), .I(vga_clk_unbuf));

333 // assign led[7] = ~clk_locked;

334 // assign led[5:1] = {6{1’b1}};

335 slow_clk slow(.clk(sys_clk),

336 .slow_clk(slow_clk));

337 // assign led[6] = ~slow_clk;

338 wire[6:0] percent_kept;

339 assign led[7:1] = ~percent_kept;

340 wire busy;

341 assign led[0] = ~busy;

342

343 ///////////////////////////////////////////////////////////////////////////////////////////////////

344 // create debounced buttons