Frequency Synthesis Only Using Integer Divide

UltraScale Architecture Clocking Resources User Guide (UG572)

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1.10.2 English

The MMCMs can also be used for stand-alone frequency synthesis. In this application, the MMCM is not used to deskew a clock network. Rather, it generates an output clock frequency for other blocks. In this mode, the MMCM feedback paths are internal, which keeps all the routing local, minimizing the jitter. This Figure shows the MMCM configured as a frequency synthesizer. In this example, an external 33 MHz reference clock is available. The reference clock can be a crystal oscillator or the output of another MMCM. Setting the M counter to 32 makes the VCO oscillate at 1056 MHz (33 MHz x 32). The MMCM outputs are programmed to provide (for example) a 528 MHz processor clock, a 264 MHz gasket clock, a 176 MHz clock, a 132 MHz memory interface clock, a 66 MHz interface, and a 33 MHz interface. In this example, there are no required phase relationships between the reference clock and the output clocks, but there are required relationships between the output clocks.

Figure 3-3: MMCM as a Frequency Synthesizer

X-Ref Target - Figure 3-3