2.4.2.2 PLL Feedback Source
If you use the PLL, you can choose to use an internal or external feedback loop, depending on your system level requirements.
Internal Feedback Loop
The following section describes the different types of internal feedback loop.
- CCC Internal—Default option.
- PLL Internal—The
triplicated PLL mode is not supported in this version of the RTG4 FCCC with
Enhanced PLL Calibration, and thus PLL Internal Feedback mode is not
available.
You can continue to use this core with Single PLL Feedback mode (all other modes except PLL Internal) to prevent the issue described in Customer Notification CN19009.
Alternatively, the triplicated PLL is available in the RTG4 FCCC core, but will be subject to the issue described in CN19009. Also refer to the RTG4 PLL Radiation Test Report to decide which PLL mode is suitable for your application’s reliability requirements.
External Feedback Loop
The external feedback is driven from the selected GL[x]/Y[x] fabric CCC output either through the fabric or externally to the chip.
- Dedicated Input Pad—The clock source is one of the four regular FPGA I/Os that have a dedicated path to the CCC.
- FPGA Fabric Input—The clock source can be one of the four input signals coming from the FPGA Fabric.
