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Technical Application Notes



Setting Gap Count for Long Cables

Technical Application Note TAN2008003

Revised June 23, 2015



Technical Application Note (TAN2008003): Setting Gap Count for Long Cables


Applicable Product(s)

  • FlyCapture SDK 
  •  Point Grey FireWire cameras


Application Note Description

This application note explains the procedures to increase the gap count on the FireWire bus. This is a requirement for cables longer than 10 meters. If gap counts are not increased appropriately, errors such as bus resets, dropped data, and poor performance can occur.


Options for Setting the Gap Count

There are two methods for setting the gap count:

  • The RegistryControlUtility (recommended)
  • The Windows Registry Editor

There are three gap count options:

  • Normal: The gap count is controlled by the MS driver. (Default)
  • Automatic: The gap count is controlled by the FirePro driver.
  • Manual: The gap count is set by the user.



The FirePro driver (PGR1394.sys) must be installed on your 1394 card(s) for automatic and manual options to work.



The gap count is maintained through reboots. However, the user must set the gap count every time a new card is installed.

Using the FlyCapture RegistryControlUtility to Set Gap Count

To access the RegistryControlUtility tab and change the gap settings:

  1. Open Registry Control Utility.
    Start Menu→All Programs→Point Grey FlyCapture2→Utilities→Registry Control Utilities
  2. Under General Settings, select the FireWire tab.
  3. Under Gap Count, select:
    1. Automatic, then click Apply.
    2. Manual: then enter a decimal value (recommended: 63) and click Apply.
    3. Normal if returning to default and click Apply.

  4. After you click Apply, this message appears: "Please disable/enable 1394 adaptors to let Gap Count change take effect." Click OK in the confirmation message.
  5. Disable/enable the card in in the device manager.


Using the Windows Registry Editor to Set Gap Count

To access the Windows Registry Editor and change the gap settings:

  1. From the Start menu, enter regit.
  2. In the Registry Editor, search for: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{361A40FB-DC46-4ED9-BFF4-068E83D5C8AF}\xxxx\Parameters
    where 'xxxx' is the installed card number.

  3. In the Parameters key, enter UsePingGapCount as a DWORD value:
    1. For Automatic, set it to 1.
    2. For Manual, set it to the required gap count (recommended: 63).
    3. For Normal, set it to 0 or a value higher than 63 (0x3F). Removing UsePingGapCount also returns it to Normal.
  4. Disable/enable the card in in the device manager.