USB 2
USB 2.0 Repeater Cable
The USB v2.0 Active Repeater Cable allows a USB device to have its cable length extended by up to
an additional 80 feet, by serially connecting 5m cables.
The USB Active Repeater Cable acts as a transparent USB hub and buffers all downstream and
upstream data traffic.
Low-speed (1.5Mbps), full-speed (12Mbps) and high-speed (480Mbps) devices will function equally
with the USB Repeater Cable.
This is not a passive extension cable but an active device. The USB Signals are buffered to ensure
signal quality and compliance with the Electrical and Timing specifications within the USB
specification. Using passive extension cables over 5m can result in errors and is not recommended.
Features include:- 5m Cable Length
- Maximum supply current drawn = 5ma
- Maximum cable voltage drop = 0.095v
- USB v2.0 & v1.1 Compliant
Please note that although it is possible to use multiple USB Active Repeater Cables in a row (up to 5
since each cable replaces a hub), users should ensure that adding the cables does not affect the
operation of the USB device.
USB Cable v1.1 and v2.0 Technical Information.
The Universal Serial Bus has the following features:
• The computer acts as the host. Only one host (which acts as a bus controller) can be connected to
a segment without a special network/datalink USB cable being used. Standard USB cables can not
be used to connect to computers as there would be two controllers on the segment.
• A USB cable has two wires for power (+5 volts and ground) and a twisted pair of wires to carry
the data. USB v2.0 cables differ in that there is individual screening around the wires in order to
prevent signal “noise”. Effective data transfer is reduced if data packets must be resent due to
interference.
• On the power wires, the computer can supply up to 500ma (milliamps) of power at 5 volts. This
however is reduced to 100ma on laptops due to limitations in the laptops PCMCIA bus. This
limitation can be overcome by powering the card, often through an external power supply, or a
special power cable that connects to either the PS2 or internal USB port.
• Low-power devices (such as Flash Drives) can draw their power directly from the bus. High-power
devices (such as printers) have their own power supplies and draw minimal power from the bus.
Hubs can have their own power supplies to provide power to devices connected to the hub. This is
also a consideration when connecting multiple devices as the 500ma available from a computer (or
100ma from a laptop) would have to be shared between all the devices connected.
• Up to 127 devices can connect to the host, either directly (if you could fit that many USB PCI or
PCMCIA cards) or by way of USB hubs.
• Individual USB cables can run as long as 5 meters. Repeater USB cables or hubs can be used so
that devices can be up to 30 meters away from the host.
• USB v1.1 allows data to be transferred at 1.5mb or 12mb per second. With USB 2.0 the bus has a
maximum data rate of 480 megabits per second. This performance may be reduced however, if the
USB cable is extended, particularly if a standard USB cable is used rather than a repeater cable.
• USB devices are hot-swappable, meaning you can plug them into the bus and unplug them any
time. The computer should report that a device has been connected or disconnected, and it may be
best to stop the device first using the icon on the task bar.
• Many USB devices can be put to sleep by the host computer when the computer enters a powersaving mode. The unpowered devices connected to a USB port rely on the USB cable to carry both
power and data.
Physical Cable Characteristics:Inside the USB cable there are two wires for power -- +5 volts (red) and ground (brown) -- and a
twisted pair (yellow and blue) of wires to carry the data. The USB cable is also shielded (externally
for USB v1.1 and individually for USB v2.0).
When the host powers up, it queries all of the devices connected to the bus and assigns each one an
address. This process is called enumeration. This process also takes place when devices are
connected to the bus during operation. The host also finds out from each device what type of data
transfer it wishes to perform:
• Interrupt - A device like a mouse or a keyboard, which will be sending very little data, would
choose the interrupt mode.
• Bulk - A device like a printer, which receives data in one big packet, uses the bulk transfer mode.
A block of data is sent to the printer (in 64-byte chunks) and verified to make sure it is correct.
• Isochronous - A streaming device (such as speakers) uses the isochronous mode. Data streams
between the device and the host in real-time, and there is no error correction.
The host can also send commands or query parameters with control packets. As devices are
enumerated, the host keeps track of the total bandwidth that all of the isochronous and interrupt
devices are requesting. They can consume up to 90 percent of the 480 Mbps of bandwidth that is
available. After 90 percent is used up, the host denies access to any other isochronous or interrupt
devices. Control packets and packets for bulk transfers use any bandwidth left over (at least 10
percent). The Universal Serial Bus divides the available bandwidth into frames, and the host
controls the frames. Frames contain 1,500 bytes, and a new frame starts every millisecond. During
a frame, isochronous and interrupt devices get a slot so they are guaranteed the bandwidth they
need. Bulk and control transfers use whatever space is left.
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