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Digital Cameras and Frame Grabbers have been around for a long time. You
would think the advantage of transmitting a digital signal would improve the
performance of the system. And in many cases it does. But with the following
problems:
Transmitting 8 or 16 bits of digital info causes you to
Need a very thick cable. Analog video can be transmitted over a single
coax cable. 8 bits of digital data requires 16 data lines (signal and ground or
for RS422 +/-). In an analog system, the data is framed by the framegrabber
board. No extra signals are needed. Digital signals need to use even more wires
to transmit framing info. And if you have more than 8 bits, add 2 wires for each
bit.
Need an expensive cable. Using 1 Coax cable for analog video is very
inexpensive. Using 16 cables for data, and another 4 or so means even the
smallest digital cables must have 20-26 conductors. Very expensive. Plus special
connectors.
Limits transmission distance. A single coax can be used for
transmitting hundreds of feet. TTL signals travel a few feet, RS422 differential
signals a few yards.
Makes integration difficult. Analog cameras interface to framegrabbers
through BNC connectors. Or a standard Hirose connector. Each digital
framegrabber has a different connector and pinout. The same is true for digital
cameras. Trying to get a many framegrabber to many digital camera matrix done is
a nightmare. To connect the camera to a framegrabber means that you must have
the specific special cable between this pair!
CAMERA LINK SOLVES THESE PROBLEMS!
Camera Link is a specification that was jointly created by camera and
framegrabber vendors that specifies a link between the camera and the
framegrabber. And it solves the problems listed above.
The cable is standard! To connect a camera link camera to a camera link
framegrabber just requires you to have a camerlink cable.
Camera Link Details
For the full spec, click here, for simple
specs, read on.
Camera Link is based on Channel Link, a set of transceivers from National
Semiconductor that take 28 bits of TTL/CMOS data , serialize it to 4 bits for
transmission via a LVDS PHY Link, then de serialize it back to 28 bits of TTL
data.
By using only 4 bits to send up to 28, Camera Link reduces the size of the
cable, the connector, and also increases the data rate of transmission. Of the
28 bits, 24 are used for data, and 4 for framing. Also 4 pair of data lines are
reserved for camera control.
Camera Link Configurations
Because some digital cameras require more than one channel link pair to
transfer data, (multi tap cameras, cameras with 32 bits of data, etc.), there
are several camera link configurations. These are explained below.
• Base—Single Channel Link chip,
single cable connector.
• Medium—Two Channel Link chips,
two cable connectors.
• Full—Three Channel Link chips,
two cable connectors.
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