HDMI Type A pinout
HDMI Pinout (Type A, 19-Pin)
HDMI type A carries video on three shielded TMDS data pairs plus a clock pair (pins 1 through 12), with the remaining pins handling control and power: CEC on 13, the utility/HEAC line on 14, DDC on 15 and 16, +5 V on 18, and hot plug detect on 19.
| Pin | Signal | Notes |
|---|---|---|
| 1 / 3 | TMDS Data2 + / − | Video data pair 2. |
| 2 | TMDS Data2 shield | Shield for the Data2 pair. |
| 4 / 6 | TMDS Data1 + / − | Video data pair 1. |
| 5 | TMDS Data1 shield | Shield for the Data1 pair. |
| 7 / 9 | TMDS Data0 + / − | Video data pair 0. |
| 8 | TMDS Data0 shield | Shield for the Data0 pair. |
| 10 / 12 | TMDS Clock + / − | TMDS clock pair. |
| 11 | TMDS Clock shield | Shield for the clock pair. |
| 13 | CEC | Consumer control bus (the reason TVs change inputs by themselves). |
| 14 | Utility / HEAC− | Reserved historically; carries ethernet/ARC functions with pin 19. |
| 15 / 16 | DDC clock / data (SCL/SDA) | The I²C channel for EDID reads and HDCP. |
| 17 | DDC/CEC ground | Return for the control lines. |
| 18 | +5 V | Source-supplied power for EDID reading (50 mA class). |
| 19 | Hot plug detect / HEAC+ | Sink signals presence; sources re-read EDID on its edge. |
What it’s used for
HDMI is unavoidable at the edges of show video: presenter laptops, playback devices, confidence monitors, and consumer displays all speak it before converters bring the signal into SDI or IP land. Understanding the control pins explains most HDMI field failures.
The handshake choreography lives on the low-speed pins: hot plug detect (19) tells the source a display exists, DDC (15/16) carries the EDID that declares supported formats, and HDCP authenticates over the same wires. Video only starts after all three succeed.
Wiring & termination notes
- Nobody solders HDMI in the field; the pinout’s value is diagnostic. Handshake symptoms (no image, wrong resolution, image drops when someone breathes) point at pins 15/16/19 paths, meaning cables, adapters, and EDID handling, not the video pairs.
- EDID managers and "EDID minders" hold a stored EDID on pins 15/16 so a switcher or projector sees a stable display; standard practice for presenter laptop inputs.
- Pin 18’s +5 V powers EDID chips in unpowered adapters; marginal cables that lose it produce the classic works-on-one-laptop-only behavior.
- Locking HDMI shells and strain relief matter: the connector was designed for the back of a television, not a tech table struck twice a day.
Frequently asked questions
What do the 19 pins of HDMI do?
Twelve carry the four shielded TMDS pairs (three data, one clock), and the rest are control: CEC, the DDC channel for EDID and HDCP, +5 V, hot plug detect, and the shared utility line used by ARC and HDMI ethernet.
What is the hot plug detect pin?
Pin 19. The display raises it to announce itself, and the source responds by reading EDID and starting the handshake. Devices that toggle it (switchers, extenders) force sources to renegotiate, which is both a tool and a failure mode.
Why does my HDMI work on one device but not another?
Usually the handshake, not the video: EDID reads failing over marginal DDC lines, HDCP refusing to authenticate through a chain, or missing +5 V/hot-plug behavior in an adapter. EDID managers and shorter, certified cables fix most of it.