a programmable bit error rate monitor includes an error counter , a monitoring period counter with a programmable upper bound to set the monitoring period , and an error flag generator that compares the actual error count to a programmable threshold . the error flag generator may generate flags at different sensitivity levels , and the user may programmably select one of those flags . the three flags can be generated by independent comparators , or they can be extrapolated from the base error flag — e . g ., by comparing only certain bits of the error count to corresponding bits of the threshold .