Which I/O mode like LVDS_25 etc.. is suitable to interface USB on a Spartan-3 FPGA ..? (I know the single ended signaling within USB). The idea being to eliminate any external usb transceiver.
I/O mode to use for USB ..?
Started by ●February 7, 2008
Reply by ●February 7, 20082008-02-07
On 7 Feb., 18:37, Sky46...@trline5.org wrote:> Which I/O mode like LVDS_25 etc.. is suitable to interface USB on a Spartan-3 > FPGA ..? (I know the single ended signaling within USB). > > The idea being to eliminate any external usb transceiver.bad idea it is possible and has been done, but its not recommended and should not be attempted for any commercial product. Antti
Reply by ●February 7, 20082008-02-07
Antti <Antti.Lukats@googlemail.com> wrote:>On 7 Feb., 18:37, Sky46...@trline5.org wrote: >> Which I/O mode like LVDS_25 etc.. is suitable to interface USB on a Spartan-3 >> FPGA ..? (I know the single ended signaling within USB). >> >> The idea being to eliminate any external usb transceiver.>bad idea>it is possible and has been done, but its not recommended >and should not be attempted for any commercial product.What are the catches, and which speeds are at least possible ..? I'm considering this mainly for prototyping. I noticed no differential modes for 3.3V are available directly. So either one have to (ab)use two LVCMOS33/LVTTL or run Vcco=3.3V in conjuction with a differential mode. How does a mode like LVDS_25 behave with Vcco=3.3V btw?
Reply by ●February 7, 20082008-02-07
Reply by ●February 7, 20082008-02-07
austin <austin@xilinx.com> wrote:>USB2 chip is now down to less than $1.>Why would you choose to suffer?Less chips, less soldering, less waiting for yet another manufacturer. At least USB-1.5Mbps and USB-12Mbps should be doable.
Reply by ●February 7, 20082008-02-07
Sky465nm@trline5.org wrote:> Less chips, less soldering, less waiting for yet another manufacturer. > At least USB-1.5Mbps and USB-12Mbps should be doable.OTOH, more wondering (and wasted time) if the reason your prototype isn't working is because you're not driving the bus correctly... -- Mark McDougall, Engineer Virtual Logic Pty Ltd, <http://www.vl.com.au> 21-25 King St, Rockdale, 2216 Ph: +612-9599-3255 Fax: +612-9599-3266
Reply by ●February 7, 20082008-02-07
Mark McDougall <markm@vl.com.au> wrote:>Sky465nm@trline5.org wrote:>> Less chips, less soldering, less waiting for yet another manufacturer. >> At least USB-1.5Mbps and USB-12Mbps should be doable.>OTOH, more wondering (and wasted time) if the reason your prototype isn't >working is because you're not driving the bus correctly...In that case I would just buy a chip+pcb to handle it. But it would really handy to be able to hookup usb devices without external circuitry. Except for some passives.
Reply by ●February 8, 20082008-02-08
On 8 Feb., 03:34, Sky46...@trline5.org wrote:> Mark McDougall <ma...@vl.com.au> wrote: > >Sky46...@trline5.org wrote: > >> Less chips, less soldering, less waiting for yet another manufacturer. > >> At least USB-1.5Mbps and USB-12Mbps should be doable. > >OTOH, more wondering (and wasted time) if the reason your prototype isn't > >working is because you're not driving the bus correctly... > > In that case I would just buy a chip+pcb to handle it. But it would really > handy to be able to hookup usb devices without external circuitry. Except for > some passives.it IS doable and has been done. But for PRODUCTION you should use real tranceiver IC. thats it. If you want to hobby prototype, it is ok to connectect directly too Antti
