USB cable size
- Thread starter hduarte
- Start date
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up to 25 depending on the cable i belive FWIW
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usb has three different speeds.
low speed (about 1 megabit iirc)
full speed (about 12 megabit)
high speed (usb 2.0 only dunno exactly how fast off hand)
mice keyboards etc tend to be low speed devices. printers scanners hubs drives etc will be full speed or high speed devices. high speed devices will fall back to full speed if plugged into a usb 1.1 port or hub.
high speed devices will fall back to full speed if plugged into a usb 1.1 port
i dunno if the official specs allow longer cables for low speed devices but it would seem logical that low speed devices would be more tolarant of cable quality issues.
low speed (about 1 megabit iirc)
full speed (about 12 megabit)
high speed (usb 2.0 only dunno exactly how fast off hand)
mice keyboards etc tend to be low speed devices. printers scanners hubs drives etc will be full speed or high speed devices. high speed devices will fall back to full speed if plugged into a usb 1.1 port or hub.
high speed devices will fall back to full speed if plugged into a usb 1.1 port
i dunno if the official specs allow longer cables for low speed devices but it would seem logical that low speed devices would be more tolarant of cable quality issues.
plugwash said:
It's 480 Mb/sec - forty times faster than "Full Speed". Don't you just love marketing hype?
Cheers,
Howard
Hi,
The USB 1.0 Spec contains a cable length limit of 5 meters, a cable delay spec of 30ns and a supply voltage minimum at any USB socket of 4.4 volts.
Chapter 7 of the spec covers the electrical specifications of the USB signals and limits all cables of any length to 30ns prop delay. Since cable varies from 3 to 6 ns per meter prop delay the maximum cable length can be calculated to be 5 meters.
This is still true for USB2.0. Though most cheaper peripherals would not work at this length due to the timing issues. You can get A-A Active Extension cables that help slightly, but would only really get you to 5m.
If you need to go beyond 5m (WHY???), then the only practical solution is to employ the use of a separately powered USB hub in the middle of 2 5m cables (but expect the occaisional problem due to both noise and attenuation at that distance).
Cheers
Merv
The USB 1.0 Spec contains a cable length limit of 5 meters, a cable delay spec of 30ns and a supply voltage minimum at any USB socket of 4.4 volts.
Chapter 7 of the spec covers the electrical specifications of the USB signals and limits all cables of any length to 30ns prop delay. Since cable varies from 3 to 6 ns per meter prop delay the maximum cable length can be calculated to be 5 meters.
This is still true for USB2.0. Though most cheaper peripherals would not work at this length due to the timing issues. You can get A-A Active Extension cables that help slightly, but would only really get you to 5m.
If you need to go beyond 5m (WHY???), then the only practical solution is to employ the use of a separately powered USB hub in the middle of 2 5m cables (but expect the occaisional problem due to both noise and attenuation at that distance).
Cheers
Merv
I
Igorian
Porker said:
That would depend on cable, connection and hub quality. There's some real tacky kit out there.
Porker said:
Unfortunately, it's the very fact that it IS a powered hub that causes the noise on the cheaper kit. The addition of extra connections on the route is what causes the attenuation, every shift from one medium to another causes a noticable drop in signal strength. Remember the 5-3-2 rule for extending ethernet! same principle.
Merv
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