///////////////////////////////////////////////////////////////////// //// //// //// Simple Baud Rate Generator //// //// //// //// //// //// Author: Rudolf Usselmann //// //// rudi@asics.ws //// //// //// //// //// //// Downloaded from: http://www.opencores.org/cores/sasc/ //// //// //// ///////////////////////////////////////////////////////////////////// //// //// //// Copyright (C) 2000-2002 Rudolf Usselmann //// //// www.asics.ws //// //// rudi@asics.ws //// //// //// //// This source file may be used and distributed without //// //// restriction provided that this copyright statement is not //// //// removed from the file and that any derivative work contains //// //// the original copyright notice and the associated disclaimer.//// //// //// //// THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY //// //// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED //// //// TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS //// //// FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL THE AUTHOR //// //// OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, //// //// INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES //// //// (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE //// //// GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR //// //// BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF //// //// LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT //// //// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT //// //// OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE //// //// POSSIBILITY OF SUCH DAMAGE. //// //// //// ///////////////////////////////////////////////////////////////////// // CVS Log // // $Id: sasc_brg.v,v 1.2 2002/11/08 15:22:49 rudi Exp $ // // $Date: 2002/11/08 15:22:49 $ // $Revision: 1.2 $ // $Author: rudi $ // $Locker: $ // $State: Exp $ // // Change History: // $Log: sasc_brg.v,v $ // Revision 1.2 2002/11/08 15:22:49 rudi // // Fixed a typo in brg // // Revision 1.1.1.1 2002/09/16 16:16:40 rudi // Initial Checkin // // // // // // // // `include "timescale.v" /* Baud rate Generator ================== div0 - is the first stage divider Set this to the desired number of cycles less two div1 - is the second stage divider Set this to the actual number of cycles Remember you have to generate a baud rate that is 4 higher than what you really want. This is because of the DPLL in the RX section ... Example: If your system clock is 50MHz and you want to generate a 9.6 Kbps baud rate: 9600*4 = 38400KHz 50MHz/38400KHz=1302 or 6*217 set div0=4 (6-2) and set div1=217 */ module sasc_brg(clk, rst, div0, div1, sio_ce, sio_ce_x4); input clk; input rst; input [7:0] div0, div1; output sio_ce, sio_ce_x4; /////////////////////////////////////////////////////////////////// // // Local Wires and Registers // reg [7:0] ps; reg ps_clr; reg [7:0] br_cnt; reg br_clr; reg sio_ce_x4_r; reg [1:0] cnt; reg sio_ce, sio_ce_x4; reg sio_ce_r ; reg sio_ce_x4_t; /////////////////////////////////////////////////////////////////// // // Boud Rate Generator // // ----------------------------------------------------- // Prescaler always @(posedge clk) if(!rst) ps <= #1 8'h0; else if(ps_clr) ps <= #1 8'h0; else ps <= #1 ps + 8'h1; always @(posedge clk) ps_clr <= #1 (ps == div0); // Desired number of cycles less 2 // ----------------------------------------------------- // Oversampled Boud Rate (x4) always @(posedge clk) if(!rst) br_cnt <= #1 8'h0; else if(br_clr) br_cnt <= #1 8'h0; else if(ps_clr) br_cnt <= #1 br_cnt + 8'h1; always @(posedge clk) br_clr <= #1 (br_cnt == div1); // Prciese number of PS cycles always @(posedge clk) sio_ce_x4_r <= #1 br_clr; always @(posedge clk) sio_ce_x4_t <= #1 !sio_ce_x4_r & br_clr; always @(posedge clk) sio_ce_x4 <= #1 sio_ce_x4_t; // ----------------------------------------------------- // Actual Boud rate always @(posedge clk) if(!rst) cnt <= #1 2'h0; else if(!sio_ce_x4_r & br_clr) cnt <= #1 cnt + 2'h1; always @(posedge clk) sio_ce_r <= #1 (cnt == 2'h0); always @(posedge clk) sio_ce <= #1 !sio_ce_r & (cnt == 2'h0); endmodule