50 Mhz pulse capture in 20 Mhz domain

A synchronizer option that can be used with a single 50MHz pulse is called a toggle synchronizer.

In the 50MHz domain, the pulses toggle a signal. The toggle signal is the input to the 20MHz domain.

In the 20MHz domain, there is a dual-DFF synchronizer, and a delay DFF, and the output of the synchronizer and delay are xored.

This will generate a single pulse in the 20MHz domain.

The pulses in the 50MHz domain must be far enough apart that the toggle exists for long enough that the 20MHz logic can see it.

Cheers,

Dave