The accurate capture of SYSREF is critical in Subclass 1 operation. The JESD204C Specification allows SYSREF to be generated in any of the following ways:
- Periodic
- One-shot
- Gapped Periodic
For maximum flexibility, the JESD204C core provides several options for how SYSREF is handled for Subclass 1 operation.
Because the JESD204C core operates using a 32-bit (4-byte) or 64-bit (8-byte) datapath, if a periodic or gapped periodic SYSREF is used in the system, the following conditions must be met:
- For 64B66B linecoding, the period must be an integer multiple of the Extended Multiblock period.
- For 8B10B linecoding, the period must be an integer multiple of the multiframe period. It must also be a multiple of 4-byte clocks. Care must be taken to ensure both of these conditions are met if the multiframe period is not a multiple of 4-byte clocks.