DCM (Digital Clock Manager)

  1. I am tasked to use the DCM in Xilinx's architecture wizard. Can anyone explain what is the function of a DCM and how does it actually work? What are the inputs and outputs of a typical DCM? many thanks!
     
  2. jcsd
  3. Check the User Guide documentation for the part you're
    using. e.g. for the Spartan 3 / Spartan 3A DCMs:
    http://direct.xilinx.com/bvdocs/userguides/ug331.pdf
    q.v. pages 61...

    Using Digital Clock Managers (DCMs)
    Summary
    Digital Clock Managers (DCMs) provide advanced clocking capabilities to Spartan-3
    Generation FPGA applications (Spartan-3, Spartan-3E, Spartan-3A, Spartan-3AN, and
    Spartan-3A DSP families). Primarily, DCMs eliminate clock skew, thereby improving
    system performance. Similarly, a DCM optionally phase shifts the clock output to delay the
    incoming clock by a fraction of the clock period. DCMs optionally multiply or divide the
    incoming clock frequency to synthesize a new clock frequency. The DCMs integrate
    directly with the FPGA’s global low-skew clock distribution network.
    Introduction
    DCMs integrate advanced clocking capabilities directly into the FPGA’s global clock
    distribution network. Consequently, DCMs solve a variety of common clocking issues,
    especially in high-performance, high-frequency applications:
    • Eliminate Clock Skew, either within the device or to external components, to
    improve overall system performance and to eliminate clock distribution delays.
    • Phase Shift a clock signal, either by a fixed fraction of a clock period or by
    incremental amounts.
    • Multiply or Divide an Incoming Clock Frequency or synthesize a completely new
    frequency by a mixture of clock multiplication and division.
    • Condition a Clock, ensuring a clean output clock with a 50% duty cycle.
    • Mirror, Forward, or Rebuffer a Clock Signal, often to deskew and convert the
    incoming clock signal to a different I/O standard—for example, forwarding and
    converting an incoming LVTTL clock to LVDS.
    • Any or all the above functions, simultaneously.
     
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