What are launch and capture flip-flops?
From PDVerse STA Mentor Guide · pdVerse Mentor Guide
Short Answer
The launch flip-flop is the one that sends data out on a clock edge (the launch edge), and the capture flip-flop is the one that captures that data on a later clock edge (the capture edge).
Example
For a simple single-cycle path between two flops running on the same clock, the capture edge is one clock period after the launch edge — data leaves the launch flop and must be captured cleanly by the capture flop one cycle later.
Why It Matters
Every setup and hold calculation is fundamentally about the relationship between when the launch flop releases data and when the capture flop needs it, so identifying which flop is which is the first step in analyzing any reg2reg path.
Mentor Note — Common Mistake
Assuming the launch and capture edges are always exactly one clock period apart — that's only true for the simplest single-cycle, same-clock case; other clocking relationships change this timing.
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