Camera Link Communication Interface for Vision Applications J. Egri 6/7/05

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

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

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

Channel Link Interface

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

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 Camera Link Interface

Base 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 –two connectors –64 bit video data –up to 5.44 Gbps aggregate bandwidth

CAMERACAMERA FRAMEFRAME GRABBERGRABBER Base Mode

CAMERACAMERA FRAMEFRAME GRABBERGRABBER Medium Mode

CAMERACAMERA FRAMEFRAME GRABBERGRABBER Full Mode

ModePorts ( 8 bit ) Supported Video data bits Number of connectors Bandwidth (clock = 85MHz) BaseA,B,C Gbps MediumA,B,C,D,E,F Gbps FullA,B,C,D,E,F,G,H Gbps Mode 1x82x83x8 1x102x101x122x121x141x16 24 RGB 4x8 3x104x103x124x12 30 RGB 36 RGB 8x8 Base  Medium  Full  Data Format

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 Strobes

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 Communications Channel

Camera control via GUI Example from Imperx Lynx Configurator camera utility

Camera control via Terminal Example from Imperx LynxTerminal camera utility

Camera download Example from Imperx LynxTerminal camera utility

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 Camera Control signals Example from Imperx FrameLink frame grabber

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. ) Advantages of Camera Link

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

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 Disadvantages of 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 Why Imperx chose Camera Link CameraHVclock (MHz) fpspayload (MBps) Base CL 204 MBps USB2 48 MBps 1394a 40 MBps 1394b 80 MBps GigE 100 MBps IPX-VGA210-L  IPX-1M48-L  IPX-2M30-L  IPX-2M30H-L  IPX-4M15-L  IPX-11M5-L  Note: Bandwidth listed is 80% of the theoretical maximum

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 Future of Camera Link