1. Communication Interface for Vision Applications
Camera Link
Communication Interface for Vision Applications
J. Egri /7/05

2. Background
Prior to Camera Link, there were a number of non-standard parallel interfaces using either LVDS or RS422 signaling
Different connectors and pinouts made cable production difficult and confusing
No standard communications method for configuring cameras existed

3. Camera Link was developed in 2000 by an industry consortium of camera and frame grabber companies
Defines a connectivity standard between digital cameras and frame grabbers
Ensures that all Camera Link products are interchangeable and interoperable
de Facto standard for high speed/high resolution imaging

4. Overview
Based on the field proven Channel Link technology developed for flat panel displays
Utilizes LVDS signaling providing higher speed, lower power and greater noise immunity
Transports synchronous digital video data and clock, a bi-directional communications channel and 4 discrete general purpose signals
Camera Link reduces the number of signals required allowing for smaller, more reliable and lower cost cables
Uses one ( for Base mode ) or two ( for Medium or Full mode ) 26 pin connectors

5. Channel Link Interface

6. Channel Link consists of a driver and receive pair
Driver accepts 28 bit single ended data plus a clock
The 28 bit data includes 24 bits of video data plus 4 strobes ( FVAL, LVAL, DVAL and spare )
Data is multiplexed 7:1 and serialized
The resulting 4 data streams plus clock are driven out over 5 LVDS pairs
Clock rate is from 20 to 85 MHz
Yields up to 2.04 Gbps ( 24 bit video data * 85 MHz )
Cable length is 10 Meters maximum

7. Camera Link Interface
Uses Channel Link for video data, strobes and clock
Uses an additional LVDS receiver and driver for a bi-directional asynchronous communications channel
Uses 4 additional LVDS pairs for 4 discrete general purpose camera control signals
Provides 3 modes: Base, Medium and Full

8. Base mode: Medium mode: Full mode: one Channel Link interface
one connector
24 bit video data
up to 2.04 Gbps aggregate bandwidth
Medium mode:
two Channel Link interfaces
two connectors
48 bit video data
up to 4.08 Gbps aggregate bandwidth
Full mode:
three Channel Link interfaces
64 bit video data
up to 5.44 Gbps aggregate bandwidth

9. G R A B E C A M E R F R A M E
Base Mode

10. G R A B E C A M E R F R A M E
Medium Mode

11. G R A B E C A M E R F R A M E
Full Mode

12. Bandwidth (clock = 85MHz)
Mode
Ports ( 8 bit ) Supported
Video data bits
Number of connectors
Bandwidth (clock = 85MHz)
Base
A,B,C 24 1
2.04 Gbps
Medium
A,B,C,D,E,F 48 2
4.08 Gbps
Full
A,B,C,D,E,F,G,H 64
5.44 Gbps
Data Format
Mode
1x8
2x8
3x8
1x10
2x10
1x12
2x12
1x14
1x16
24 RGB
4x8
3x10
4x10
3x12
4x12
30 RGB
36 RGB
8x8
Base b
Medium
Full

13. Strobes FVAL ( Frame Valid ) - envelopes all lines in a frame
LVAL ( Line Valid ) envelopes all pixels in a line
DVAL ( Data Valid ) qualifies valid pixels in a line

14. Communications Channel
Used to configure camera’s operating parameters
On the Imperx Lynx cameras: Also used to upload new firmware, software and lookup tables into the camera
Two LVDS signals for asynchronous serial communications
Frame Grabber–to–Camera communications
Camera–to–Frame Grabber communications
ASYNC format : 1 start, 8 data bits, 1 stop, 0 parity, no handshaking
BAUD rates : 9600 bps to Kbps
Standard API using clser***.dll ensures interoperability between camera configuration software and frame grabber

15. Camera control via GUI
Example from Imperx Lynx Configurator camera utility

16. Camera control via Terminal
Example from Imperx LynxTerminal camera utility

17. Camera download
Example from Imperx LynxTerminal camera utility

18. Camera Control signals
4 general purpose camera control signals ( CC1-CC4 )
Driven by the Frame Grabber to the Camera
Use is defined by the camera vendor
Often used as a software trigger
Often used to control the camera exposure
Example from Imperx FrameLink frame grabber

19. Advantages of Camera Link
Industry tested and proven technology
Easy camera/frame grabber integration
Camera Link products are interchangeable and interoperable
Standardized DLL based API for camera configuration
Higher bandwidth and lower latency than competing interfaces
Point-to-point interface yields deterministic data transfer rate
Full use of available bandwidth for payload. No protocol overhead or encapsulation penalty
Processing can be performed in frame grabber hardware rather than by CPU ( i.e. Bayer interpolation, table look up, frame averaging, pixel reordering, etc. )

20. Image is DMA’ed directly into system or video memory by the frame grabber freeing up the CPU
Multiple cameras processed on frame grabber ( i.e. Zygo uses four Lynx cameras operating at 210 fps each for flat panel inspection )
Embedded serial communications channel for camera configuration
Embedded discrete camera control signals
Comprehensive set of video data modes supported
Connectors, data format and control signals are all standardized
Smaller cable size improves reliability and reduces cost
Industry standard cable results in competitive pricing

21. Disadvantages of Camera Link
Cable length is limited to 10 meters. This can be solved by using repeaters ( such as the Imperx model CLCL ) or fiber converters
Requires a frame grabber
Power is not supplied over the Camera Link cable and therefore cameras require a second connector for power

22. Why Imperx chose Camera Link
We use high resolution Kodak CCD sensors which produce large video payloads and require high bandwidth transport
Our customers demand low latency response for real time applications
Camera H V
clock
(MHz)
fps
payload
(MBps)
Base CL
204 MBps
USB2
48 MBps
1394a
40 MBps
1394b
80 MBps
GigE
100 MBps
IPX-VGA210-L
640
480 40
210
96.77 b r s
IPX-1M48-L
1000 48
72.00
IPX-2M30-L
1600
1200 33
95.04
IPX-2M30H-L
1920
1080
102.64
IPX-4M15-L
2048 15
94.37
IPX-11M5-L
4000
2672 28 5
80.16
Note: Bandwidth listed is 80% of the theoretical maximum

23. Future of Camera Link New specification v1.1 ratified by AIA
Adds additional functionality to the clser***.dll API for the serial interface
Provides reference source code to committee members
New draft in development:
Adds additional video modes
Introduces Honda miniature Camera Link connector
Introduces new smaller diameter cable ( 28 vs. 26 gauge conductors )
Adds ‘power over cable’ capability