Article ID: 000076138 Content Type: Troubleshooting Last Reviewed: 02/13/2006

What is the <courier>EXTSWITCH</courier> device feature of the Stratix™ phase-locked loop (PLL) used for?


  • PLL
    Description The CLKSWITCH feature of the Stratix device's PLLs can be used to switch between PLL inputclocks of different frequencies or for redundant clocks. For example, if extclk0 is 66 MHz and extclk1 is 100 MHz, the designer can control the switch from extclk0 to extclk1.

    On the other hand, the automatic clock-sense circuitry can monitor primary and secondary clock sources and automatically switch from the primary clock to the secondary clock in the event that the primary clock stops toggling.

    The manual clock switchover feature using EXTSWITCH is useful when clock sources originate from multiple cards on the backplane, requiring a manual switchover between two frequencies of operation. You should choose the secondary clock frequency so that the voltage controlled oscillator (VCO) operates within the recommended range of 500 to 1100 MHz. You can set the M and N counters accordingly to keep the VCO operating frequency in the recommended range.

    You can use the EXTSWITCH feature for applications where the user wants to switch back to the primary clock from the secondary, once the primary is stable again.

    Related Products

    This article applies to 1 products

    Stratix® FPGAs



    All postings and use of the content on this site are subject to Terms of Use.