Camera Link
Encyclopedia
Camera Link is a serial communication protocol designed for computer vision
applications based on the National Semiconductor
interface Channel-link
. It was designed for the purpose of standardizing scientific and industrial video products including cameras, cables and frame grabbers. The standard is maintained and administered by the Automated Imaging Association
or AIA, the global machine vision
industry's trade group.
s to represent up to 24 bits of pixel
data and 3 bits for Video Sync signals.
These consist of Data Valid, Frame Valid, and Line Valid bits. The data are serialized 7:1, and the four data streams and a dedicated clock are driven over five LVDS pairs. The receiver accepts the four LVDS data streams and LVDS clock, and
then drives the 28 bits and a clock to the board.
The camera link standard calls for these 28 bits to be transmitted over 4 serialized
differential pair
s with a serialization factor of 7. The parallel data clock is transmitted
with the data. Typically a 7x clock must be generated by a PLL or SERDES
block in
order to transmit or receive the serialized video. To deserialize the data,
a shift register
and counter
may be employed. The shift register
catches each of the serialized bits, one at a time,
then registers the data out into the parallel clock domain - once
the data counter has reached its terminal value.
/s (255 MB
/s).
/s (510 MB
/s). The "Full" configuration adds another 16-bits to the data path, resulting in a 64-bit wide video path that can carry 5.44Gbit
/s (680 MB
/s).
/s (850 MB
/s).
Computer vision
Computer vision is a field that includes methods for acquiring, processing, analysing, and understanding images and, in general, high-dimensional data from the real world in order to produce numerical or symbolic information, e.g., in the forms of decisions...
applications based on the National Semiconductor
National Semiconductor
National Semiconductor was an American semiconductor manufacturer, that specialized in analog devices and subsystems,formerly headquartered in Santa Clara, California, USA. The products of National Semiconductor included power management circuits, display drivers, audio and operational amplifiers,...
interface Channel-link
Channel-link
Channel-Link by National Semiconductor is a high-speed interface for cost-effectively transferring data at rates from 250 megabits/second to 6.4 gigabits/second over backplanes or cables...
. It was designed for the purpose of standardizing scientific and industrial video products including cameras, cables and frame grabbers. The standard is maintained and administered by the Automated Imaging Association
Automated Imaging Association
Automated Imaging Association is the world's largest machine vision trade group. AIA has more than 300 members from 30 countries, including system integrators, camera, lighting and other vision components manufacturers, vision software providers, OEMs and distributors...
or AIA, the global machine vision
Machine vision
Machine vision is the process of applying a range of technologies and methods to provide imaging-based automatic inspection, process control and robot guidance in industrial applications. While the scope of MV is broad and a comprehensive definition is difficult to distil, a "generally accepted...
industry's trade group.
Transmission protocol
The base Camera Link standard uses 28 bitBit
A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...
s to represent up to 24 bits of pixel
Pixel
In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....
data and 3 bits for Video Sync signals.
These consist of Data Valid, Frame Valid, and Line Valid bits. The data are serialized 7:1, and the four data streams and a dedicated clock are driven over five LVDS pairs. The receiver accepts the four LVDS data streams and LVDS clock, and
then drives the 28 bits and a clock to the board.
The camera link standard calls for these 28 bits to be transmitted over 4 serialized
differential pair
Differential pair
A differential pair is a pair of conductors used for differential signaling. Differential pairs are usually found on a printed circuit board, in cables , and in connectors...
s with a serialization factor of 7. The parallel data clock is transmitted
with the data. Typically a 7x clock must be generated by a PLL or SERDES
SerDes
A Serializer/Deserializer is a pair of functional blocks commonly used in high speed communications to compensate for limited input/output. These blocks convert data between serial data and parallel interfaces in each direction...
block in
order to transmit or receive the serialized video. To deserialize the data,
a shift register
Shift register
In digital circuits, a shift register is a cascade of flip flops, sharing the same clock, which has the output of any one but the last flip-flop connected to the "data" input of the next one in the chain, resulting in a circuit that shifts by one position the one-dimensional "bit array" stored in...
and counter
Counter
In digital logic and computing, a counter is a device which stores the number of times a particular event or process has occurred, often in relationship to a clock signal.- Electronic counters :...
may be employed. The shift register
Shift register
In digital circuits, a shift register is a cascade of flip flops, sharing the same clock, which has the output of any one but the last flip-flop connected to the "data" input of the next one in the chain, resulting in a circuit that shifts by one position the one-dimensional "bit array" stored in...
catches each of the serialized bits, one at a time,
then registers the data out into the parallel clock domain - once
the data counter has reached its terminal value.
Base configuration
The "Base" Camera Link configuration carries signals over a single connector/cable. The cable used is a MDR ("Mini D Ribbon") 26-pin Male Plug Connector, optimized by 3M for the LVDS signal. In addition to the 5 LVDS pairs transmitting the serialized video data (24 bits of data and 4 framing/enable signals), the connector also carries 4 LVDS discrete control signals and 2 LVDS asynchronous serial communication channels for communicating with the camera. At the maximum chipset operating frequency (85 MHz), the base configuration yields a video data throughput of 2.04 GbitGigabit
The gigabit is a multiple of the unit bit for digital information or computer storage. The prefix giga is defined in the International System of Units as a multiplier of 109 , and therefore...
/s (255 MB
Megabyte
The megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000...
/s).
Medium/Full configuration
The Camera Link specification includes higher-bandwidth configurations that provide additional video data paths over a second connector/cable. The "Medium" configuration doubles the video bandwidth, adding an additional 24 bits of data and the same 4 framing/enable signals present in the "Base" configuration. This yields a 48-bit wide video data path capable of throughput up to 4.08 GbitGigabit
The gigabit is a multiple of the unit bit for digital information or computer storage. The prefix giga is defined in the International System of Units as a multiplier of 109 , and therefore...
/s (510 MB
Megabyte
The megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000...
/s). The "Full" configuration adds another 16-bits to the data path, resulting in a 64-bit wide video path that can carry 5.44Gbit
Gigabit
The gigabit is a multiple of the unit bit for digital information or computer storage. The prefix giga is defined in the International System of Units as a multiplier of 109 , and therefore...
/s (680 MB
Megabyte
The megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000...
/s).
Other extended configurations
Some camera and data acquisition hardware manufacturers have extended the bandwidth of the interface beyond the limits imposed by the Camera Link interface specification. These formats extend the width of the "Full" configuration by reassigning some of the redundant framing/enable signals to produce a data path width of up to 80-bits over two connectors/cables, which further increases the video bandwidth. The 80-bit video path can carry 6.8 GbitGigabit
The gigabit is a multiple of the unit bit for digital information or computer storage. The prefix giga is defined in the International System of Units as a multiplier of 109 , and therefore...
/s (850 MB
Megabyte
The megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000...
/s).
Signal data
Interface Standard Specifications
The Camera Link standard is maintained by AIA. The introduction of the Camera Link Interface Standard (1.0) was released in October 2000. Revision 1.1 was adopted in January 2004, with expanded software function support. The standard committee adopted version 1.2 in January 2007, introducing mini SDR ("Shrunk D Ribbon") connectors (SDR-26) and power over Camera Link (POCL). Annex D of revision 1.2 adds mechanical and electrical descriptions to the standard, especially cable performance. Annex E of revision 1.2 lists requirements of POCL equipment.See also
- GigE visionGigE visionGigE Vision is an interface standard introduced in 2006 for high-performance industrial cameras. It provides a framework for transmitting high-speed video and related control data over Ethernet networks. The standard was initiated by a group of 12 companies and the committee has since grown to...
- List of device bandwidths
- Low-voltage differential signaling (LVDS)