On Tue, Aug 01, 2006 at 08:19:42AM -0400, Timothy Miller wrote: > On 8/1/06, Koen De Vleeschauwer <[EMAIL PROTECTED]> wrote: > >I've been wondering which DVI dotclocks will be available on OGD1. > >There seem to be three oscillators; 13.5 MHz, 14.318 MHz and 44.647 MHz. > >13.5 Mhz is a well-known sample rate for digital TV, > >14.318 MHz a well-known sample rate for NTSC (and used in PCs). > >Where does the 44.647 MHz come from? > > I don't recall exactly what Howard put on there, but the Xilinx DCMs > are capable of producing clocks with a variety of different multiplier > and divider values.
Yes, you can program the DCM (digital clock managers) to multiply an incoming frequency by a fraction n/d, where n=2..32, and d= 1..32. On Virtex-4 you can reconfigure these factors on the fly while the FPGA is running. (check "Use reconfiguration pins" in the wizard). I could be wrong, but AFAIK the multiply/divide factors of the Spartan-3 DCM can only be specified statically, in the verilog source, as // synthesis attribute. There has been a small thread about this on comp.arch.fpga "Programmable frequency synthesizer with Xilinx DCM". http://www.fpga-faq.com/archives/87700.html > Subject: Re: Programmable frequency synthesizer with Xilinx DCM > From: "Peter Alfke" <[EMAIL PROTECTED]> > Date: 2 Aug 2005 15:09:39 -0700 > > Present generation: Spartan3 plus external PLL for higher freq. and > less jitter.( <100 ps) > Next generation: Virtex-4 FX (needs MGTs) > Peter Correct me if I'm wrong, but I only see three possibilities: - using an external PLL. I see no external PLL in the schematic, however. - using a PLL in another chip on the board, eg. the Conexant. CLKO of the Conexant seems unconnected, however. - or reloading the FPGA with a different bitstream whenever the modeline dotclock changes. Which do you use? regards, koen _______________________________________________ Open-graphics mailing list [email protected] http://lists.duskglow.com/mailman/listinfo/open-graphics List service provided by Duskglow Consulting, LLC (www.duskglow.com)
