DVI TMDS Clock Ground Pin Assignment

This article explains the pinout configuration for Digital Visual Interface (DVI) connectors, focusing specifically on the ground pin assignment for the Transition-Minimized Differential Signaling (TMDS) clock line. Understanding this pin assignment is essential for cable design, hardware repair, and troubleshooting signal integrity issues in digital video connections.

The TMDS Clock Ground Pin

In standard DVI connectors (including DVI-D and DVI-I, single-link and dual-link configurations), the ground assignment for the TMDS clock is Pin 22.

In the official DVI specification, this pin is designated as the TMDS Clock Shield. It acts as the dedicated ground reference and electromagnetic interference (EMI) shield for the differential clock pair.

TMDS Clock Pin Group

The TMDS clock signal relies on a three-pin differential configuration to transmit timing information alongside video data channels. The pins associated with the clock signal are located adjacent to one another on the connector:

• Pin 22: TMDS Clock Shield (Ground)
• Pin 23: TMDS Clock + (Positive differential line)
• Pin 24: TMDS Clock − (Negative differential line)

Function of Pin 22

Because DVI relies on high-speed serial data transmission, maintaining clean signal edges and minimizing cross-talk between the data channels and the clock line is critical. Pin 22 provides an isolated ground shield that surrounds the twisted pair running to Pin 23 and Pin 24.

This shielding prevents external radio frequency interference (RFI) from corrupting the clock synchronization, ensures impedance matching (nominally 100 ohms differential), and provides the return path for common-mode currents.