Allegedly, on or about 15 December 2015, Fred Smith sent: > there is definitely a limit on USB cable length, and for some > devices its very strict. I have a Canon LIDE 210 USB scanner here. > I had originally put together cables long enough to reach from the > shelf by my desk to the computer, and it totally failed to work when > using that cabling. it works only if I hold it on my lap (no room on > the desk) so that the USB cable is no more than 4-5 feet long. > > I've used much longer USB cables with a Brother laser printer, but > I was probably pushing my luck there, since the standard does > specify rigid cable length limits. There's specifications for 1.5 megabit/sec (low-speed) of 3 metres, and 12 megabit/sec (full-speed) of 5 metres for USB 1.1. And USB 2.0 specifies 480 megabits/sec (hi-speed) of 5 metres. Apparently USB 3.0 doesn't specify a maximum cable length, but the practicality of signalling (*) parameters places it at 3 metres. * It's not just data going down a wire, there's handshaking, as well. The timing of data and handshaking response is critical. Introduce too much delay (due to cabling length, or its electrical characteristics), and every transmission becomes mistimed. Those are the full end-to-end cabling lengths, including the wiring inside the device from one device's electronic circuits to the other device's circuitry. Hence a 5 metre connecting cable actually exceeds the specifications. There are ways to correctly exceed these lengths between equipment that's placed too far apart, and that's to have cables with electronics inside them (probably in the connectors). It may be possible to simply use a hub in the middle, but I haven't researched that. It's worth noting that some cabling will be horribly inferior. If you split apart cheap cabling (perhaps the one supplied with your equipment), you may find very thin wiring that simply runs in parallel to each other inside the sheath. The data pair of wires should be twisted around each other, to minimise the effects of outside interference to the data signals. So replacing cabling *may* be enough to resolve a problem. You may find that the header cabling in some desktop PCs (from motherboard to front-panel connectors) is inferior. I had one that just used ribbon cable. -- [tim@localhost ~]$ uname -rsvp Linux 3.9.10-100.fc17.x86_64 #1 SMP Sun Jul 14 01:31:27 UTC 2013 x86_64 All mail to my mailbox is automatically deleted, there is no point trying to privately email me, I will only read messages posted to the public lists. Lucky for you I typed this, you'd never be able to read my handwriting. -- users mailing list users@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe or change subscription options: https://admin.fedoraproject.org/mailman/listinfo/users Fedora Code of Conduct: http://fedoraproject.org/code-of-conduct Guidelines: http://fedoraproject.org/wiki/Mailing_list_guidelines Have a question? Ask away: http://ask.fedoraproject.org
