APPLICATION NOTE Comparison of Basler BCON and Camera Link Interfaces Applicable to Basler dart BCON cameras only Document Number: AW001394 Version: 01 Language: 000 (English) Release Date: 09 September 2016 INTERNAL USE ONLY (Set it to white if you do not need it)
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Table of Contents 1 Introduction... 2 2 Physical Layer: LVDS... 2 3 Link Layer: Channel Link... 3 4 Configurations... 3 5 Connectors and Cables... 6 6 Power Supply... 8 7 Camera Configuration... 9 8 Image Acquisition... 11 9 Conclusion... 12 Revision History... 14 Comparison of Basler BCON and Camera Link Interfaces 1
1 Introduction Basler is a leading global producer of digital cameras for industrial applications. Manufacturers of equipment, machines, and plants integrate our cameras into their own products. Our premium cameras are mainly used in industrial mass production, medical technology, the life sciences, retail applications, as well as in intelligent traffic systems. To address the increasing demand on embedded computing systems, Basler introduced the Basler dart BCON camera series in 2016. Based on the newly developed BCON for LVDS (Low Voltage Differential Signaling) interface, which we refer to as Basler BCON in this document, Basler enables companies and developers involved in the embedded technology to meet challenging requirements and to achieve the leanest Machine Vision integration into embedded processing equipment. The Basler BCON interface offers the highest flexibility for connecting with LVDS-based technology like FPGA (Field Programmable Gate Array) boards and SoCs (Systems on a Chip). Therefore, Basler BCON is ideal for many applications, as it fits with a broad variety of systems and adjusts to the requirements needed. This allows for the most efficient digital image processing and thus an optimized total cost of ownership for your vision system. Due to its similarities to other LVDS-based interfaces, e.g. Channel Link and Camera Link, the Basler BCON interface may be also a perfect fit for companies and developers who are familiar with LVDS and consider switching to the embedded technology. This application note provides a thorough comparison between the Basler BCON and Camera Link interfaces. For more information about Basler dart BCON cameras, see www.baslerweb.com. 2 Physical Layer: LVDS The electrical standard used by both Basler BCON and Camera Link is LVDS, i.e. low voltage differential signaling. Every signal is carried by two wires, with a voltage difference of 350 mv. The low signal swing allows for achieving a theoretical maximum transmission rate of 3.125 Gbit/s and makes the LVDS standard independent of any particular supply voltages. LVDS is also characterized by low power consumption and noise immunity to ±1 V common volt noise. Basler BCON The current Basler dart BCON camera specification specifies a minimum voltage difference of 247 mv and a maximum voltage difference of 600 mv. The recommended nominal common mode voltage is 1.25 V ± 10%. For more information about LVDS, refer to the LVDS Owner s Manual: http://www.ti.com/lit/ml/snla187/snla187.pdf For more information about Basler dart BCON cameras, refer to the Basler dart BCON User s Manual. The document can be downloaded from www.baslerweb.com. Comparison of Basler BCON and Camera Link Interfaces 2
3 Link Layer: Channel Link Both Basler BCON and Camera Link are based on a Channel Link LVDS chipset, DS90CR28x, manufactured by National Semiconductor. Channel Link chipsets of the DS90CR28x series support 28-bit bus width. Channel Link chipsets in 21- and 48-bit parallel bus widths are also available, but as they are not used in Basler BCON or in Camera Link, they are not further considered in this document. A Channel Link chipset consists of a driver (transmitter) and receiver pair. It is used to transfer digital data. The chipsets have a 3.3 V supply and operate with a clock speed of 85 MHz. The transmitter converts 28 bits (data is serialized 7:1) of CMOS/TTL data into four LVDS data streams. The data is transmitted with every cycle of the transmit clock, which is also referred to as word clock (f wclk ). The receiver converts the LVDS data streams back into 28 bits of CMOS/TTL data. Using a transmit clock with a frequency of up to 85 MHz, 28 bits of TTL data is transmitted at 595 Mbit/s per LVDS channel. With four data channels, the total data throughput is 2.38 Gbit/s (297.5 Mbyte/s). In the Channel Link protocol, 28 bits of data are transferred over just 4 pairs of wires. A fifth pair is used to transfer a required clock signal. Thus, seven bits are transmitted per link, LSB first. The accompanying serial frame clock signal has a duty cycle of 4/7. Camera Link uses serial frame clocks between 40 and 85 MHz. Basler BCON uses serial frame clocks (f wclk ) between 20 and 84 MHz in increments of 8, i.e. 20 MHz, 28 MHz, 36 MHz, etc. For more information about Channel Link, refer to the National Semiconductor Channel Link Design Guide: http://www.ti.com/lit/ml/snla167/snla167.pdf 4 Configurations Camera Link Camera Link comes in five variants: Lite, Base, Medium, Full and 80-bit (also called Deca ). The Lite and Base configurations use only one 4-channel Channel Link transmitter and require only one cable. Medium uses two transmitters and receivers, Full and Deca use three, and they all require two cables. Each chip can transmit up to 4 * 7 = 28 bits per clock cycle. On Camera Link Lite, Base, Medium and Full configurations, each clock cycle transmits a frame valid bit, a line valid bit, and a data valid bit. One bit remains unassigned. On Camera Link 80-bit configuration, only frame valid and line valid bits are transmitted. This results in the following number of pixel data bits per data transfer: Lite configuration: 10 bits Base configuration: 24 bits Medium configuration: 48 bits Full configuration: 64 bits 80-bit configuration: 80 bits Comparison of Basler BCON and Camera Link Interfaces 3
In Camera Link, the data bits are divided into eight 8-bit ports, which are also referred to as taps. They are denoted by capital letters starting with port A, which contains bits 0 (LSB) to 7 (MSB). The standard prescribes exactly how pixel data is assigned to the ports. For more information on the pixel data assignment, refer to the Camera Link specification which is freely available at www.visiononline.org. Basler BCON Basler BCON is comparable to Camera Link s Base configuration and also uses a single 4-channel Channel Link transmitter and requires a single cable. The Channel Link chip can transmit up to 4 * 7 = 28 bits per clock cycle on up to four data lanes referred to as Data Lane X0 to X3. Each clock cycle transmits a frame valid, line valid and two BCON output bits. Table 1: Basler BCON Data Serialization The two BCON output bits are new compared to Camera Link. They are always transmitted on data lane X0 at position 0 and 1. Depending on the camera model, the following BCON output signals can be available: Flash Window Exposure Active User Output 1 User Output 2 The remaining 24 bits are reserved for the image data channel including frame information (FrameInfo), pixel data and line checksums (Cksum X). Figure 1: Basler BCON Image Data Flow The FrameInfo packet is specific to the Basler BCON interface and is sent before each frame transmission. It includes information about the pixel format valid for the following pixel data and the Comparison of Basler BCON and Camera Link Interfaces 4
number of pixels per clock cycle. This allows the user to identify what data is being transmitted by the camera and to configure the user-specific deserializer accordingly. To identify the command word of the FrameInfo, all 24 bits in the data channel are set to zero upon each transition of the FVal or LVal signal from 1 to 0. For more information on image acquisition, refer to Chapter 8. The actual number of bits and active data lanes used depends on the data being transmitted, i.e. whether 8-bit, 12-bit, 16-bit or 24-bit pixel data is being transmitted (see Table 2 and Table 3). Similar to Camera Link, the Basler BCON interface does not provide data flow control. In contrast to the Camera Link interface, the BCON interface does not provide a data valid bit (DVal). Only FVal and LVal are used as synchronization signals. Although the bit clock f bclk is not transmitted, it can be calculated using the parallel clock frequency. The bit clock must be 7 times faster than the word clock frequency: f bclk = f wclk * 7 Pixels per Clock Cycle Unlike Camera Link, Basler BCON does not specify any taps. However, the number of pixels to be transmitted per clock cycle can be set. In the current Basler BCON specification the user can decide on transmitting either one or two pixels per clock cycle. The One Pixel per Clock Cycle mode is available for all pixel formats. In this mode, pixel data is being transmitted as follows: Table 2: Data Channel Usage in One Pixel per Clock Cycle Mode Comparison of Basler BCON and Camera Link Interfaces 5
The Two Pixel per Clock Cycle mode is available for 8-bit and 12-bit pixel formats only. In this mode, pixel data is being transmitted as follows: Table 3: Data Channel Usage in Two Pixel per Clock Cycle Mode 5 Connectors and Cables Camera Link Figure 2 shows the Camera Link connector pin numbers at camera end. Besides the four data links and the single pixel clock link, there are four configurable input lines for camera control (e.g. for applying an external hardware trigger to the camera) and a bidirectional serial interface. The serial interface serves to adjust camera settings and is typically RS-644 LVDS compatible. The pinout below applies to normal-sized standard connectors used for Camera Link. Pin 1 is usually marked with a small triangle. These connectors are called MDR-26 (26-pin Mini Delta Ribbon). Such connectors are e.g. used on Basler aviator Camera Link cameras. Figure 2: Pin Numbering of a Camera Link MDR-26 Connector Smaller connectors, also called MiniCL, are also allowed by the standard, i.e. HDR-26 and SDR- 26 (Honda Delta Ribbon / Shrunk Delta Ribbon). SDR-26 connectors are e.g. used on Basler ace and Basler beat Camera Link cameras. Figure 3: Back Side of Basler ace and Basler beat Camera Link Cameras Equipped with Two SDR-26 Connectors Comparison of Basler BCON and Camera Link Interfaces 6
The non-data connector pins have the following functions: Camera/Grabber Pin Signal Description 1, 13,14, 26 Inner shield Digital ground in camera 1, 26 PoCL: 12 V Power over Camera Link 4 W Table 4: Non-Data Connector Pins in a Standard Camera Link Connector The Camera Link standard does not specify a maximum cable length. The cable length is instead limited by the electrical requirements outlined in the Camera Link standard. Camera Link cables with up to 10 meters length are available. Basler BCON The Basler dart BCON camera is interfaced to external circuitry via a 28-pin flat flexible cable (FFC) connector by Hirose Electric Co. The connector order code is Hirose FH41-28S-0.5SH (05). The connector allows camera integration into embedded systems with both FPGAs and SoCs (Systems on a Chip). Figure 4: Basler BCON Cameras Equipped with a 28-Pin Flat Flexible Cable (FFC) Connector For more information on the 28-pin FFC connector by Hirose Electric Co., refer to: http://www.hirose.co.jp/cataloge_hp/ed_fh41_20140305.pdf The FFC connector provides connections for LVDS image transfer, I/O signals (e.g. for applying an external trigger signal), and power supply. Furthermore, three I²C lines are integrated, which are used for camera configuration via the Basler pylon Camera Software Suite. Comparison of Basler BCON and Camera Link Interfaces 7
Figure 5: FFC Connector Pin Positions of a Basler BCON Camera The Basler BCON specification does not specify a fixed cable length. It is instead limited by the quality of the given FFC cable. Standard FFC cables can reach a length of up to 1-2 meters. The FFC connector is specifically designed for shielded and impedance-controlled FFC cables. However, standard FFC cables without a ground layer can be also used. Figure 6: Flat Flexible Cable Used for Basler BCON Cameras 6 Power Supply Camera Link The Camera Link standard specifies for a frame grabber dedicated to PoCL (Power over Camera Link) operation to supply 12 V ±1 V and to be capable of supplying 4 W per cable over the full voltage range. The 4 W must be available at camera end of the cable, which means that a frame grabber has to take account of possible power loss in the cable. When Camera Link cameras are powered with auxiliary power, the different Camera Link camera manufacturers are free to specify the camera power supply requirements according to their own needs. Basler Camera Link cameras are typically specified for 12 V ±1 V. However, Basler beat cameras are also specified for power supply of up to 24 V (+5%). Comparison of Basler BCON and Camera Link Interfaces 8
Basler BCON The Basler BCON interface specifies the following input voltage ranges: Table 5: Recommended Input Voltages for the Basler BCON Interface (Power Supply, LVDS Input, I²C) The voltage ranges for the four LVDS data lanes and one LVDS clock line are specified as follows: Table 6: Recommended Output Voltages for the Basler BCON Interface (LVDS Outputs) 7 Camera Configuration Camera Link The Camera Link standard allocates two LVDS pairs for asynchronous serial communication between the camera and the frame grabber. Both cameras and frame grabbers should support at least 9600 baud rate. All Camera Link compliant frame grabbers must be supplied with a DLL file that describes the characteristics of a serial port built into the frame grabber. This serial port is used for communication between the PC and the camera via the Camera Link interface. The name of the file supplied by the frame grabber manufacturer has the form clser***.dll, where *** is determined by the manufacturer of the grabber and usually represents the manufacturer s name. To communicate with Basler Camera Link cameras, e.g. Basler ace, Basler beat, or Basler aviator, Basler offers the Basler pylon Camera Software Suite. The pylon software uses the clser***.dll to configure the serial port of the frame grabber. Once a connection is established, the pylon Viewer tool or the pylon SDKs can be used to configure Basler Camera Link cameras. Comparison of Basler BCON and Camera Link Interfaces 9
Basler BCON The Basler BCON interface uses a standard I²C interface for the camera configuration. The I²C interface consists of three lines: I2C_SDA (I²C interface data line), I2C_SCL (I²C interface clock line), and I2C_ID (I²C line to define the slave address that the camera should respond to). The I2C_ID line can be also used to reset a camera if necessary. A Basler BCON camera is an I²C slave device that can handle data transfers at up to 400 kbit/s ( Fast-mode according to I²C). Currently, up to two cameras can be connected to a single I²C bus. The logical level of the 2C_ID line determines which slave address is used (i.e. to which the camera should respond). Table 7: I²C Slave Addresses Used by Basler BCON Cameras For more information on the I²C standard, refer to I²C-Bus Specification and User Manual: http://www.nxp.com/documents/user_manual/um10204.pdf To configure Basler BCON cameras, the Basler pylon Camera Software Suite, version 5.0.5 or higher is required. The Basler pylon Camera Software Suite is available for Windows, Linux (x86 or ARM), and OS X operating systems. The pylon BCON interface is currently supported on Linux x86 and ARM operating systems only. Camera configuration is performed via the I²C bus of the Linux system and adheres to the GenICam standard. The required driver adapter is provided by pylon as a sample implementation including source code and a precompiled binary. Basler pylon introduces a new C programming interface the BCON Adapter API - which lets the user create their own I²C adapter by implementing this interface. Users may take the pylon sample implementation as a blueprint for their own adapter code or simply use the precompiled binary without any modification. The document Programmer's Guide and API Reference for a BCON Adapter library used with pylon describes how to implement, install, and debug a BCON Adapter library. It is included in the pylon Camera Software Suite. For more information about the Basler pylon Camera Software Suite, visit www.baslerweb.com. For more information about the GenICam standard, visit http://www.emva.org/ Comparison of Basler BCON and Camera Link Interfaces 10
8 Image Acquisition Camera Link To acquire images from Camera Link cameras, a compatible Camera Link frame grabber is required. The frame grabber is needed to de-serialize the serialized image data by the camera and assemble it to complete images. For a camera to operate properly with a given frame grabber, the correct frame grabber camera file must be installed first. In essence, the camera file informs the frame grabber about how the pixel information coming from the camera will be ordered and about the bit depth of the pixel data. Depending on the frame grabber supplier, there can be a separate camera file for each combination of camera model and pixel data format or a camera file may cover several different camera models. Typically, each frame grabber supplier has a different naming scheme for their camera files. For example, Matrox refers to the camera files for their frame grabbers as Digital Configuration Files or DCF files and National Instruments refers to theirs as Interface Camera Descriptors or ICD files. Camera files appropriate for the given Camera Link camera are usually supplied by the given frame grabber manufacturer. The frame grabber manufacturers also supply a software for viewing acquired images. Basler BCON The Basler dart BCON cameras are designed to connect with LVDS-based technology like FPGA (Field Programmable Gate Array) boards and SoCs (Systems on a Chip). However, such embedded systems usually vary from one embedded system manufacturer to another, e.g. a Xilinx SoC is different than an Altera SoC. Also, the systems vary by platform generation, e.g. the Xilinx Zynq TM -7000 SoC is different than the Xilinx Zynq UltraScale+ MPSoC. Due to the fact that the Basler pylon camera software suite does not know which LVDS image acquisition hardware is actually used, the user must develop his own implementation for image data transfer. The new pylon BCON adapter API can also be used to develop an image acquisition solution for the image grabbing hardware actually used. After doing so, pylon can be used without limitation even for image data transfer. Comparison of Basler BCON and Camera Link Interfaces 11
Figure 7: Camera Control and Image Acquisition Concept for Basler BCON Cameras When Using the Basler pylon Camera Software Suite To enable companies and developers to easily evaluate and design in Basler dart BCON cameras, Basler offers a development kit called PowerPack for Embedded Vision. It contains a processing board based on the Xilinx Zynq TM -7000 SoC, a Basler dart BCON camera (daa2500-14bc), a lens, and other accessories. The development kit demonstrates how the camera can be controlled via I 2 C and how image streaming can be performed using a standard Xilinx Vivado IP Core and the Zynq Programmable Logic (Zynq FPGA). 9 Conclusion In a nutshell, both the Basler BCON interface and Camera Link are quite similar in terms of using LVDS as an electrical standard and using Channel Link chipsets for serializing, de-serializing and transmitting image data. Camera Link comes in five variants (Lite, Base, Medium, Full, and 80-bit) and uses a different bit order than Basler BCON. Basler BCON is similar to the Camera Link Base configuration by using a single Channel Link chipset. However, BCON uses only two synchronization bits and defines whether one or two pixels are to be transferred per clock cycle instead of defining taps as in Camera Link. Camera Link specifies connectors and cables that are designed for Machine Vision industrial applications, which require longer cable lengths and some extent of protection against electro- Comparison of Basler BCON and Camera Link Interfaces 12
magnetic interferences (EMI). This requires Camera Link cables to be relatively bulky and less flexible. The Basler BCON interface is designed for embedded applications and uses flat flexible cable (FFC) connectors and cables. Thus, both the Basler dart BCON cameras and the FFC cables are coming in a very compact form factor, which makes them a perfect fit for embedded systems. The power supply requirements are also tailored to the application fields the cameras are designed for and used in. Camera Link specifies a power supply voltage of 12 V for frame grabbers supporting PoCL and lets the choice of the supported auxiliary power supply range to the camera manufacturers. Basler Camera Link cameras usually support auxiliary power supply voltages from 12 to 24 V. Basler BCON specifies a voltage of 5 V, which is typical for embedded systems. For camera control, Camera Link specifies using a serial port that is integrated into the Camera Link frame grabber. Camera Link frame grabber manufacturers provide a DLL file that describes the characteristics of the serial port and enables the camera manufacturer software to establish a control communication channel between the camera and the frame grabber. The Basler BCON interface uses a standard I²C interface for the camera configuration and comes with three I²C lines in total. The required I²C driver adapter for Linux x86 and ARM operating systems is provided by the Basler pylon Camera Software Suite either as a sample implementation including source code and a precompiled binary. Image acquisition in Camera Link is done by means of a Camera Link frame grabber that deserializes the camera image data and assembles it in complete images. The images are then further processed in the Camera Link frame grabber software. As being designed to connect with FPGA (Field Programmable Gate Array) boards and/or SoCs (Systems on a Chip), and due to the high variety and differences among the different embedded hardware platforms, the image transfer from Basler dart BCON cameras has to be implemented by the user. To enable the evaluation and design-in process of Basler dart BCON cameras, Basler offers a development kit based on the Xilinx Zynq TM -7000 SoC. The development kit demonstrates implementing the image pipeline. Users can take the sample implementation and use it on compatible Xilinx platforms or port it to other embedded systems from other manufacturers. Comparison of Basler BCON and Camera Link Interfaces 13
Revision History Document Number Date Changes AW00139401000 09 Sep 2016 Initial release version of this document. Comparison of Basler BCON and Camera Link Interfaces 14