Using the Acquisition Modes of Analog IMAQ Devices

Publish Date: Sep 08, 2011 | 12 Ratings | 3.83 out of 5 |  PDF

Overview

Overview
The IMAQ PCI/PXI-1407, the IMAQ PCI/PXI-1408, and the IMAQ PCI-1409 have selectable acquisition modes to fit the needs of various applications. All modes are configurable from the interface property page in Measurement & Automation Explorer (MAX). The modes discussed in this document are:
  • Standard Mode
  • CSYNC External Mode
  • External Lock Mode—IMAQ 1408 and 1409 only
  • External HSYNC/VSYNC Mode—IMAQ 1409 only
  • External HSYNC/VSYNC (HLOCK only) Mode—IMAQ 1409 only
Each section of this document contains applications for each acquisition mode, required physical connections, a description of the behavior of the IMAQ device, and the triggering issues associated with each mode.

Table of Contents

  1. Acquisition Modes Reference
  2. Standard Mode
  3. CSYNC External Mode
  4. External Lock Mode
  5. External HSYNC/VSYNC Mode
  6. External HSYNC/VSYNC (HLOCK only) Mode

1. Acquisition Modes Reference


The table below outlines your options for each acquisition mode. See the sections following this table for a more detailed description of each mode.


Acquisition Mode Supported IMAQ Devices Camera Types Asynchronous Reset Required Connections When to Use
Standard 1407
1408
1409
Standard* No Video One-shot or continuous applications from a standard camera
CSYNC External 1407
1408
1409
Standard* No Video
CSYNC
Standard video signal in which CSYNC is not present in the video signals

RGB StillColor Mode
External Lock Mode † 1408
1409
Nonstandard Yes Video
HSYNC
VSYNC
PCLK
Nonstandard or asynchronously-resettable cameras
External HSYNC/VSYNC Mode 1409 Standard* No Video
HSYNC
VSYNC
Standard video signals in which HSYNC and VSYNC are not present in the video signals
External HSYNC/VSYNC (HLOCK only) Mode 1409 Standard* Yes Video
HSYNC
VSYNC
Standard video signals that support asynchronous reset

† The supplied pixel clock should not exceed the maximum pixel clock frequency of your IMAQ device.

*Note: Not all analog IMAQ devices support all standards. Use the list below to determine the standard supported by each IMAQ device.

  • 1407: RS-170, CCIR
  • 1408: RS-170, CCIR, NTSC, PAL
  • 1409: RS-170, CCIR, NTSC, PAL, and Progressive Scan (25, 30, 50 or 60 Hz)

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2. Standard Mode

Use Standard Mode for most applications, including one-shot or continuous acquisitions from a standard video signal. Refer to the Acquisition Modes Reference section above to determine the standard mode for each IMAQ device.

In Standard Mode, you need only connect the composite video signal to the video input of the IMAQ device. Because a composite signal contains both the timing information and the video data in one signal, the IMAQ device has everything it needs to acquire an image. The timing information (CSYNC) in the composite signal is passed into circuitry that generates an internal HSYNC, VSYNC, and pixel clock according to the selected video standard. The device then uses this timing information to sample the video data so that the NI-IMAQ driver can reconstruct it into an image.

If you use NI-IMAQ to set up a triggered acquisition in Standard Mode, the camera’s timing does not change in response to a trigger supplied to one of the external trigger lines. When you apply a trigger, you acquire the first frame that occurs after the trigger. For example, if the timing between VSYNC pulses is 33ms (such as on a camera that runs at 30 frames per second), a 33ms gap of uncertainty occurs between the trigger and the acquired frame. For more precise timing, use a camera that supports asynchronous reset, and configure the IMAQ device in either External Lock Mode or External HSYNC/VSYNC (HLOCK only) Mode.

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3. CSYNC External Mode

Use CSYNC External Mode for one-shot or continuous acquisitions from cameras that provide the timing information and the video data on different lines, which can include both monochrome and RGB StillColor applications. In both cases, the video signal should be a standard supported type.

For monochrome cameras, connect the video signal to the video input of the IMAQ device, and connect the CSYNC from the camera to the CSYNC input of the IMAQ device. In this case, CSYNC is passed into circuitry that generates an internal HSYNC, VSYNC, and pixel clock according the selected video standard.

RGB StillColor applications work very much like the monochrome applications. However, in most cases, RGB StillColor applications do not require a separate timing signal. Typically, RGB cameras provide the timing information on one of the three video data lines (usually the green signal). Connect the R, G, and B video lines to video input channels 1, 2, and 3, respectively. Next, select CSYNC External Mode from the Acquisition Mode list box in MAX. Select the channel containing the CSYNC from the CSYNC Source list box.

The same triggering issues that exist in Standard Mode also exist in CSYNC External Mode.

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4. External Lock Mode

Use External Lock Mode for nonstandard video signals and for asynchronous triggering applications in which a pixel clock signal is provided to the IMAQ device.

In External Lock Mode, the camera provides 4 signals to the IMAQ device: video data, HSYNC, VSYNC, and pixel clock (PCLK). In External Lock Mode, the IMAQ device does not need to “lock” to any timing signals. Instead, the PCLK signal is used as the sample clock for the internal A/D, and the HSYNC and VSYNC signals are used directly to provide line and field information.

Note: When using External Lock Mode, you cannot drive the pixel clock faster than the maximum PCLK capability of the IMAQ device (20 MHz for the IMAQ 1408, and 40 MHz for the IMAQ 1409).

If you have an analog camera that has a nonstandard output, you can still acquire images with your IMAQ device as long as you do not exceed the maximum PCLK rate of the IMAQ device. Select External Lock Mode and provide the HSYNC, VSYNC, and PCLK connections described above. Be sure to use a camera file that accurately describes your camera. In MAX, you can select Generic Area Scan camera as a template and adjust the values in the Basic and Advanced tabs to meet the camera specifications.

Cameras that support asychronous reset also work in External Lock Mode. When an asynchronously-resettable camera receives a trigger, it changes its timing to immediately output a frame. This abrupt change in timing can throw off the locking circuitry used by Standard and External CSYNC Modes. However, since the External Lock Mode bypasses that circuitry, you can still use your IMAQ device to acquire from an asynchronously-resettable camera. The setup is the same as described above for nonstandard output, but it is unnecessary to create a new camera file if the video output is standard.

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5. External HSYNC/VSYNC Mode

Use External HSYNC/VSYNC Mode when you have a standard video source that outputs HSYNC and VSYNC on separate lines and when there is no timing information present in the video data signal itself, such as the VGA output of a computer’s video card.

In External HSYNC/VSYNC Mode, you must supply HSYNC, VSYNC, and at least one channel of video data. The IMAQ device locks to the timing provided on both the HSYNC and the VSYNC lines. The device then internally generates its own pixel clock and uses it to sample the selected video signal.

The same triggering issues that exist in Standard Mode also exist in External HSYNC/VSYNC Mode.

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6. External HSYNC/VSYNC (HLOCK only) Mode

Use the External HSYNC/VSYNC (HLOCK only) Mode with standard analog cameras that support asynchronous reset. Asynchronous reset is a triggering feature supported by some analog cameras in which the vertical timing of the camera’s output changes in response to a trigger. This feature is useful for applications that require very precise timing. However, because ensuring that the IMAQ device is synchronized with the camera is critical to acquiring a good image, the interface is somewhat more complicated.

When the IMAQ device is in the External HSYNC/VSYNC (HLOCK only) Mode, it locks only to the HSYNC of the camera and waits for a pulse. When a pulse is received on the VSYNC pin of the IMAQ device, the device begins acquiring on the next HSYNC pulse.

To use this setup, connect the HSYNC signal and video data coming from the camera to the IMAQ device. Connect the trigger source to the trigger input of the camera, and connect the VSYNC signal on the IMAQ device to a frame-ready signal. The frame-ready signal should be unasserted while the camera is waiting for a trigger, and should pulse once when the camera is ready to output the image. This pulse typically comes at least one exposure period after the trigger is sent to camera, and is not the same signal as the trigger itself.

Many cameras provide such a frame-ready signal. If your camera does not provide this signal, you can use the pulse generation feature of the 1409 to provide this signal for you. To use this feature, split the trigger source to go to both the camera and to an external trigger on the 1409—let’s assume EXT0. Next, configure the 1409 to generate a pulse on EXT1 some set time after the trigger is received on EXT0. This length of time is camera-specific, but will always be at least the exposure time of the camera. To set this time, use the Delay Pulse parameter in the Generate Pulse function. This signal becomes your frame-ready signal and is routed externally to the VSYNC input of the 1409.

Some cameras require that HSYNC be supplied to them when in asynchronous reset mode. Any source can provide this signal, including another camera or a National Instruments Data Acquisition (DAQ) device. If it is convenient for your application, you can also use the IMAQ PCI-1409 itself as the source. From the Advanced tab of the camera's property page in MAX, you can turn on HSYNC for control lines 0 through 3. The 1409 will then generate an HSYNC of the proper frequency for the video standard selected.

 

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