Data Arrives Before the Setup Window Closes - Electronic Circuits IV & XII: Digital Logic and Timing Closure Step by Step

A data-arrives-before-the-setup-window-closes ledger checks whether data reaches the latch early enough before the selected clock edge. The stated 8 s edge, 5 s data arrival, 2 s setup window, and 1 s setup slack are exact only for the ideal timing-row model. Real timing closure adds clock skew, jitter, PVT variation, delay distributions, metastability risk, probe calibration, finite precision, and measurement uncertainty.

Setup and hold both pass when their slack values are nonnegative. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

Data must arrive before the setup window closes

The selected edge is at 8 seconds, and data arrives at 5 seconds.

8\ \text{s}+(-5\ \text{s})+(-2\ \text{s})=1\ \text{s}

Passing rows keep both slacks nonnegative

Each row recomputes setup and hold slack from arrival and next-change times.

\begin{array}{c|c|c|c}t_D&t_{\text{next}}&s_{\text{setup}}&s_{\text{hold}}\\4\ \text{s}&10\ \text{s}&2\ \text{s}&1\ \text{s}\\5\ \text{s}&10\ \text{s}&1\ \text{s}&1\ \text{s}\\6\ \text{s}&11\ \text{s}&0\ \text{s}&2\ \text{s}\\\end{array}

The next change must wait through the hold window

The next data change is at 10 seconds, leaving 1 second of hold slack.

10\ \text{s}+(-8\ \text{s})+(-1\ \text{s})=1\ \text{s}