DS280DF810: PRBS generation function

Hi Expert, 

I have look through the PRBS function needed in E2E. I understand there must be input signal for PRBS generator. but still have a detailed question. 

• The retimer PRBS generator channel requires some input signal for its CDR to lock to. This signal may be a sub-rate clock signal at frequency multiple of programmed data rate. Please confirm the PRBS generator has a reference input signal and its CDR is locked 

For this thread, I find the PRBS generator will work with sub-rate clock signal and CDR lock, so what is the range of sub-rate clock, div 8 or div 16? for 27.9gbps, what is the min input signal frequency? thanks. 

Also there is same question for 56G CDR, DS560DF810, it is better if you could also share the sub-rate clock range of input signal in PRBS generator mode. 

BR

Chi