HDMI Interface Basics: Version History, Pin Definitions, and EDID, CEC, ARC, HDCP

HDMI (High-Definition Multimedia Interface) is the most common video interface on TVs, monitors and set-top boxes. A single cable carries video, audio and multiple control signals, with several "invisible" mechanisms working together inside. This article briefly explains HDMI’s version evolution and pin definitions, as well as EDID, CEC, ARC and HDCP — concepts often mentioned but rarely explained clearly.

1. Version History: From 1080P to 8K

Version	Published	Max Bandwidth	Key Capabilities
HDMI 1.0	2002	4.95Gbps	1080P@60Hz — first single-cable audio/video transmission
HDMI 1.3	2006	10.2Gbps	Deep Color, lossless audio Dolby TrueHD
HDMI 1.4	2009	10.2Gbps	4K@30Hz, ARC audio return, HDMI Ethernet Channel
HDMI 2.0	2013	18Gbps	4K@60Hz, HDR, 21:9 widescreen
HDMI 2.1	2017	48Gbps	8K@60Hz / 4K@120Hz, eARC, VRR variable refresh rate, ALLM

Simple rule of thumb: every big step in bandwidth enables a big step in resolution and refresh rate. Cables must keep up too — full HDMI 2.1 requires "Ultra High Speed" certified cables.

2. Pin Definitions: 19 Pins, Each with a Job

The most common HDMI Type-A connector has 19 pins, divided into four groups:

• TMDS high-speed data (pins 1–9):3 shielded differential data pairs carrying all video and audio data;
• TMDS clock (pins 10–12):1 differential clock pair providing the timing beat for data transfer;
• Control & low-speed signals (pins 13–17, 19): CEC control, DDC (SCL/SDA, for reading EDID), hot-plug detect (HPD), etc.;
• +5V power (pin 18): The source supplies a small current to the sink for level shifting and detection.

Pin	Signal	Function
1	TMDS Data2+	High-speed differential data channel 2 positive (video/audio data)
2	TMDS Data2 shield	Data channel 2 shield ground
3	TMDS Data2−	High-speed differential data channel 2 negative
4	TMDS Data1+	High-speed differential data channel 1 positive
5	TMDS Data1 shield	Data channel 1 shield ground
6	TMDS Data1−	High-speed differential data channel 1 negative
7	TMDS Data0+	High-speed differential data channel 0 positive
8	TMDS Data0 shield	Data channel 0 shield ground
9	TMDS Data0−	High-speed differential data channel 0 negative
10	TMDS Clock+	Differential clock positive, providing the timing beat for data transfer
11	TMDS Clock shield	Clock channel shield ground
12	TMDS Clock−	Differential clock negative
13	CEC	Consumer electronics control bus — devices remotely control each other
14	Utility / HEAC+	From HDMI 1.4, used for ARC audio return (single-ended signal); from 2.1, the eARC differential positive
15	SCL	DDC clock line, for reading EDID
16	SDA	DDC data line, for reading EDID
17	DDC/CEC ground	Reference ground for DDC and CEC
18	+5V power	The source supplies a small current to the sink for detection and power
19	Hot-plug detect HPD / HEAC−	Detects device insertion and triggers EDID reading; also serves as the ARC/eARC return channel reference

3. EDID: The Display’s "Self-Introduction"

EDID (Extended Display Identification Data) is a small block of data stored in a display device, recording "who I am, which resolutions and refresh rates I support, my audio capabilities" and more. As soon as a source is plugged in via HDMI, it reads the EDID through the DDC channel (pins 15, 16) and automatically outputs a format the display supports — which is why a TV lights up at the right resolution as soon as it is connected. EDID problems are a common cause of "no picture when plugged in" and "wrong resolution".

4. CEC: One Remote Controls All Devices

CEC (Consumer Electronics Control) runs on pin 13, letting devices on the same HDMI link control each other: operate a set-top box with the TV remote; power on a game console and the TV switches input and turns on automatically. Brands call it different names (Samsung Anynet+, Sony BRAVIA Sync), but they are all CEC.

5. ARC / eARC: Sending Audio "Backwards" to the Speaker

ARC (Audio Return Channel, introduced in HDMI 1.4) lets a TV send audio "backwards" along the same HDMI cable to an amplifier or soundbar, eliminating a separate audio cable. It uses the pin 14 (Utility/HEAC+) and pin 19 (HPD/HEAC−) return-channel pair. eARC (HDMI 2.1) has higher bandwidth and can return lossless surround sound such as Dolby Atmos. Testing a TV’s ARC function requires a signal source or dedicated device to simulate the return link.

6. HDCP 1.4 and HDCP 2.2: The "Encryption Lock" for Content

HDCP (High-bandwidth Digital Content Protection) encrypts audio/video in transit to prevent mid-path recording. When playing 4K Blu-ray or licensed streaming content, the entire chain — source, cable and display — must pass HDCP authentication:

• HDCP 1.4: an older version from the 1080P era, still widely used today;
• HDCP 2.2: mandatory for 4K/8K content, with stronger encryption and stricter authentication; if any link in the chain only supports 1.4, licensed 4K content goes black or degrades.

When testing TV mainboards on production lines, whether the HDCP handshake passes is a mandatory item — which requires the test signal source itself to have legitimate HDCP 1.4/2.2 bidirectional authentication capability.

7. What It Means for Display Testing

HDMI testing is far more than "does a picture come out": correct EDID reading, successful HDCP handshakes, CEC command response and normal ARC return are all items of whole-set FCT testing. Yuanwei Technology’s video pattern generator products (such as SVG-2201 and SUC-211) support HDMI 2.1 output with built-in EDID read/write and HDCP 1.4/2.2 authentication, enabling one-stop automated testing of all HDMI items for TV mainboards and whole sets.