AV.link

AV.link is a control protocol carried over SCART connections, standardized by CENELEC as EN 50157-1 (1998). It enables automated control and status communication between connected AV devices using a single-wire serial data bus on pin 10 of the SCART connector. AV.link is also known by various manufacturer trade names including SmartLink (Sony), Q-Link (Panasonic), EasyLink (Philips), MegaLogic (Grundig), and nexTViewLink.

History

Before AV.link was standardized, the SCART connector already carried basic signaling on pin 8 (status/aspect ratio) and pin 16 (blanking/RGB select), which allowed rudimentary automatic input switching and RGB/composite signal selection. However, these were simple DC voltage levels rather than a true communication protocol.

The origins of AV.link trace back to earlier proprietary systems, particularly the D²B (Domestic Digital Bus), a bidirectional serial communication protocol developed in the 1980s for interconnecting consumer electronics. D²B was itself standardized as IEC 61030 and used the same physical pin (pin 10) on SCART connectors for data communication. However, D²B saw limited consumer adoption due to complexity and manufacturer fragmentation.

CENELEC standardized AV.link as EN 50157-1 in 1998, providing a simpler, more focused protocol specifically for the SCART ecosystem. The standard was organized into multiple parts: EN 50157-1 covered general requirements, EN 50157-2-1 addressed automatic signal quality matching and source device selection, EN 50157-2-2 defined basic system-oriented commands, and EN 50157-2-3 specified system-oriented applications.

AV.link gained broad adoption on European CRT televisions and VCRs throughout the late 1990s and 2000s, with most major manufacturers implementing the protocol under their own trade names. It was particularly popular in combination with VCR timer recording features and electronic programme guide (EPG) systems like nexTView.

Protocol Specifications

Parameter	Value
Standard	CENELEC EN 50157-1 (1998)
Physical layer	Single-wire serial bus, open-collector
SCART pin	10 (data), with pin 12 as data return ground on some implementations
Pull-up voltage	3.0–3.3 V (passive)
Bus speed	333 bit/s
Fall time	50 μs
Rise time	250 μs
Bit duration	2.4 ± 0.35 ms
Logic 1 (low period)	0.6 ± 0.2 ms
Logic 0 (low period)	1.5 ± 0.2 ms
Max bus capacitance	7,300 pF (10 devices × 100 pF + 9 cables × 700 pF)

AV.link uses an open-collector bus configuration where any connected device can pull the data line low. Each bit begins with a falling edge, and the duration of the low period determines its value — a short low pulse represents a logic 1, while a longer low pulse represents a logic 0. The relatively slow 333 bit/s data rate and generous timing tolerances ensured reliable operation over the long, unshielded cables common in consumer SCART installations.

Features

AV.link provided several automation capabilities that improved the consumer experience with SCART-connected equipment:

Automatic input switching — When a source device (e.g., VCR, DVD player) powers on and begins outputting a signal, the connected television automatically selects the appropriate SCART input and wakes from standby if necessary.
Signal quality negotiation — Devices communicate to determine the highest-quality signal path available. If both support RGB, the system automatically selects RGB over S-Video or composite, ensuring optimal picture quality without manual configuration.
Aspect ratio signaling — Source devices can instruct widescreen-capable televisions to switch between 4:3 and 16:9 display modes. This complemented the basic voltage-level signaling already available on SCART pin 8.
Standby synchronization — Turning off the television can automatically place connected source devices into standby, and vice versa, reducing the need to manage multiple remote controls.
VCR timer recording coordination — The protocol facilitated automated timer recording by allowing EPG-equipped devices to program connected VCRs, a feature particularly associated with the nexTViewLink branding.

Trade Names

Different manufacturers marketed their AV.link implementations under proprietary names, though all were interoperable to varying degrees:

Trade name	Manufacturer
SmartLink	Sony
Q-Link	Panasonic
EasyLink	Philips
MegaLogic	Grundig
nexTViewLink	Various (EPG-related feature)
Data Logic	Metz
AV Compu Link	Sharp

Relationship to HDMI CEC

AV.link's functionality was carried forward into HDMI's Consumer Electronics Control (CEC) feature, which provides similar one-wire serial bus automation for digital connections. CEC operates on pin 13 of the HDMI connector and offers comparable capabilities — automatic input switching, system standby, remote control pass-through, and device discovery. CEC itself is marketed under various trade names (Anynet+ by Samsung, BRAVIA Sync by Sony, SimpLink by LG), echoing the fragmented branding that characterized AV.link. The conceptual lineage from D²B through AV.link to HDMI CEC represents a continuous evolution of consumer electronics automation over three decades.

References