Transcript PowerPoint-presentatie

Interfaces
A practical approach.
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Contents les 3
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USB (1996)
Universal Serial Bus
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Contents les 3 USB Goals
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It had to be a solid, cheap port that
also for cheap peripherals if mice could
be used.
The cost of cabling and connectors
were not high.
The construction had to be so, that
erroneous connection was excluded.
There were many devices can be
connected via USB at the same time.
USB had to provide sufficient speed
printers and other fast as hard drives .
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Signal rates
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•A low-speed rate of 1.5 Mbit/s (~183 kB/s) is defined by USB
1.0. It is very similar to "full-bandwidth" operation except each
bit takes 8 times as long to transmit. It is intended primarily to
save cost in low-bandwidth human interface devices (HID)
such as keyboards, mice, and joysticks.
•The full-speed rate of 12 Mbits/s (~1.43 MB/s) is the basic
USB data rate defined by USB 1.1. All USB hubs support fullbandwidth.
•A high-speed (USB 2.0) rate of 480 Mbit/s (~57 MB/s) was
introduced in 2001. All hi-speed devices are capable of falling
back to full-bandwidth operation if necessary; they are
backward compatible. Connectors are identical.
•A SuperSpeed (USB 3.0) rate of 4800 Mbit/s (~572 MB/s). USB
3.0 connectors are generally backwards compatible, but
include new wiring and full duplex operation.
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USB connections
The standard USB A plug (left) and B plug (right)
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Pin 1
VCC (+5 V)
Pin 2
Data-
Pin 3
Data+
Pin 4
Ground
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USB connections
With USB is much more possible than with a parallel port or serial
port, while there are fewer wires are used. This is made possible by
the USB protocol.
A USB connection consists of four wires
:+5 volt,
nul,
differential data (D- en D+).
The two data-wires as ' twisted pair ' used to differential data to
send: When a ' 0 ' the voltage on the pen for D- is higher than the
voltage on the pen for D +, and for a ' 1 ' is the voltage on the pin for
D-lower than the voltage on the pen for D +. For low speed (1.5
Mbit/s) and full speed (12 Mbit/s) the transmitter must provide a
voltage of at least 2,5 volts between the D-and D + -pens, while for
high speed (480 Mbit/s) the transmitter must ensure a stream of
17.8 mA
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USB Cable lenght /Power
•Max lenght 5m round trip delay 1,5ns
•4.75 5.25 V
•Unit load 100 mA
•USB 2.0 port has max 5 unit loads
•Impedance 90 Ohm
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USB Cable lenght /Power
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USB Cable lenght /Power
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