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DVI Interfaces and
Their Connectors Reference Guide
Digital
Visual Interface,
a digital
interface
standard created by the Digital
Display Working Group (DDWG) to
convert analog signals into digital
signals to accommodate both analog and digital monitors. It is
designed for carrying uncompressed digital video data to a display.
Basically, video data from the video
source (video adaptor) is transmitted as binary data, representing
each pixel's level of illumination within the binary data. When the
display is driven at its native resolution, it will read each binary
number and apply that brightness to the appropriate pixel on the
monitor. When driven at its native resolution, each binary data
packet sent will correspond with directly to one pixel on the
monitor. This gives you a cleaner, crisper display than analog,
where a neighboring pixel's illumination can affect all the pixels
around it. Analog is also a victim of noise, electrical distortions,
etc, etc, whereas digital, or DVI, is not affected by these
disturbances.
Just as a reference, vga signals vary
the amplitude of the analog signal to show differences in
brightness. Higher amplitudes of a vga signal corresponds to a
brighter pixel. DVI use binary data to indicate the level of
brightness desired. Thus the output is a more accurate
representation of the true image intended.
There are two
standards being used:
"DVI-I" stands
for "DVI-Integrated" and supports both digital and
analog transfers, so it works with both digital and
analog monitors. "DVI-D" stands for "DVI-Digital"
and supports digital transfers only.
Connector Types - Single Link or Dual Link:
DVI uses an
interface called TMDS or
Transition Minimized Differential Signaling. DVI
specifications call for at least one TMDS "link" to
transmit data, though there are DVI specifications
that have what's called dual links or two TMDS
channels. A single link has three data channels (RGB)
and one clock control channel.
Single Link
A single DVI link
consists of four twisted pairs of wires (red, green,
blue, and clock) to transmit 24 bits of data per
pixel. With a single DVI link, the largest
resolution possible at
60 Hz is 2.75
megapixels or a maximum screen resolution at 60 Hz
of 1915 x 1436 pixels (standard 4:3 ratio),
1854 x 1483 pixels (5:4
ratio) or
2098 x 1311 (widescreen 8:5 ratio)
Dual Link
The DVI connector therefore has
provision for a second link, containing another set of red, green,
and blue twisted pairs. When more bandwidth is required than is
possible with a single link, the second link is enabled, and
alternate pixels may be transmitted on each, allowing resolutions up
to 4 megapixels at 60 Hz. The second link can also be used when more
than 24 bits per pixel is required. The data pairs carry binary data
at ten times the pixel clock reference frequency, for a maximum data
rate of 1.65 Gbit/s x 3 data pairs for a single DVI link.
Some Specs
Each link in the DVI standard is made
up of 3 data channels for RGB information and has a maximum
bandwidth of 165 Mhz; this equates to 165 million pixels per second.
Color support is up to 24-bit depth, 8 bits per color. Each incoming
8-bit color data word is encoded by the DVI standard into a 10-bit
transition minimized DC-balanced character, meaning that each pixel
is represented by a total of 30-bits. This means that effective data
throughput over a single link DVI cable is 4.95Gbps while in
the case of dual link DVI, max. data throughput is 9.9Gbps.
Below is a connector
guide:
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The DVI standard specifies a
DVI
connector based on a 24 pin
layout - however only 12 are implemented in
a single link DVI interconnect.
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DVI-D
- True Digital Video
DVI-D cables are used for
direct digital connections between
source video (namely, video
cards) and digital LCD (or rare CRT)
monitors. This provides a
faster, higher-quality image than with
analog, due to the nature of
the digital format. All video cards
initially produce a digital
video signal, which is converted into
analog at the VGA output. The
analog signal travels to the monitor
and is re-converted back into a
digital signal. DVI-D eliminates the
analog conversion process and
improves the connection between
source and display
DVI-A -
High-Res Analog
DVI-A cables are used to carry
a DVI signal to an analog display,
such as a CRT monitor or budget
LCD. The most common use of
DVI-A is connecting to a VGA
device, since DVI-A and VGA carry
the same signal. There is some
quality loss involved in the digital to
analog conversion, which is why
a digital signal is recommended
whenever possible.
DVI-I - The
Best of Both Worlds
DVI-I cables are integrated
cables which are capable of transmitting
either a digital-to-digital
signal or an analog-to-analog signal.
This makes it a more versatile
cable, being usable in either digital or
analog situations.
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Please note
that a DVI-D cable will not work on an analog
system, nor a DVI-A on a digital system. To connect
an
analog
source to a digital display, you'll need a VGA to
DVI-D electronic convertor; to connect a digital
output to an analog monitor, you'll need to use a
DVI-D to VGA convertor.
How
Will I Know Which Cable To Use?
Determining which
type of DVI cable to use for your products is
critical in getting the right cable the first
time.
Check both of the
female DVI plugs to determine what signals they
are compatible with.
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If one or both
connections are DVI-D, you need a DVI-D
cable.
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If one or both
connections are DVI-A, you need a DVI-A
cable.
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If one
connection is DVI and the other is VGA,
and the DVI is analog-compatible, you
need a
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DVI to VGA
cable or a DVI/VGA adaptor.
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If both
connections are DVI-I, you may use any DVI
cable, but a DVI-I cable is recommended.
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If one
connection is analog and the other
connection is digital, there is no way to
connect them
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with a single
cable.
-
You'll have to
use an electronic convertor box, available
in either analog VGA to digital DVI or
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digital DVI to
analog VGA.
A most important
difference when selecting your DVI connector is
analog support - look at the receptacles on your
devices to determine if they can take the four pins
around the flat blade on the DVI connector.
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A flat blade
alone denotes a DVI-D connection.
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If there are
two holes above and two holes below the flat
blade, then it is either a DVI-I or a DVI-A.
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In other words,
you would then need to determine whether
both the digital and the analog
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modes are
enabled on your DVI port -- check your
user's manual.
Picture It
In this type setup the PC is generating
zero's and one's for the video signal. The typical CRT can only
display analog signals. Therefore your VGA graphics card makes the
conversion through the D/A converter.
In this setup we
have DVI to DVI. Digital to Digital. Best scenario to have.
To Summarize the
connectors :
DVI-I Single-link Connector
DVI-I Cables
are integrated cables which are capable of
transmitting either a digital-to-digital
signal or an analog-to-analog signal. This
makes it a more versatile cable, being
usable in either digital or analog
situations. This DVI-I Single-link
connector is similar to the dual-link DVI-I,
but it carries only a single TMDS link. |
DVI-I Dual-link Connector
DVI-I Cables
are integrated cables which are capable of
transmitting either a digital-to-digital
signal or an analog-to-analog signal. This
makes it a more versatile cable, being
usable in either digital or analog
situations. This DVI-I Dual LInk Connector
appears almost identical to the dual-link
DVI-D connector except that it has an
additional four pins that surround the flat
offset ground bar. This is because the DVI-I
interface was designed to carry both digital
and analog signals. However, most DVI
displays and video sources are DVI-D, and
the female ports do not contain sockets to
accept the four extra analog pins. As a
result, DVI-I cables are limited to a narrow
range of applications such as certain KVM
switches. Also note that the offset ground
bar on a DVI-I plug is larger than the one
on a DVI-D plug. This means that a DVI-I
connector cannot fit into a DVI-D socket
simply by removing the four analog pins. |
DVI-D Single-link Connector
DVI-D Cables
are are used for direct digital connections
between source video (namely, video cards)
and digital LCD (or rare CRT) monitors. This
provides a faster, higher-quality image than
with analog, due to the nature of the
digital format. All video cards initially
produce a digital video signal, which is
converted into analog at the VGA output. The
analog signal travels to the monitor and is
re-converted back into a digital signal. DVI-D
eliminates the analog conversion process and
improves the connection between source and
display. This DVI-D single-link connector
has 18 pins. The male plug has them arranged
in two groups of nine pins, with the flat
ground bar off to one side. A single-link
interface provides one TMDS link. |
DVI-D Dual-link Connector
DVI-D are used
for direct digital connections between
source video (namely, video cards) and
digital LCD (or rare CRT) monitors. This
provides a faster, higher-quality image than
with analog, due to the nature of the
digital format. All video cards initially
produce a digital video signal, which is
converted into analog at the VGA output. The
analog signal travels to the monitor and is
re-converted back into a digital signal. DVI-D
eliminates the analog conversion process and
improves the connection between source and
display. This DVI-D Dual link connector
contains 24 pins, arranged in three
horizontal rows of eight pins. To the side
of this grouping of 24 pins is a wide, flat
pin called a ground bar. A dual-link
interface provides two TMDS links, or groups
of data ��channels�� that can carry
more than 10 Gbps of digital video
information. A dual-link cable is
backwards-compatible with single-link
applications. The majority of DVI
applications will use this DVI-D dual-link
cable connection. |
Connector to
Connector Cable Guide
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