• Mohit Kalra

Do you know your TV remote?

Lockdown, courtesy Covid-19 (not to anyone’s surprise) has forced me into spending more time than usual with my TV over the weekends and in the process helped us find some of the hidden features of my TV remote as well. Do you know, your TV remote can control most of the HDMI connected devices? You do not need a remote controller for your set-top boxes (STBs) or Fire TV type devices as most of the functions can be carried out with your regular TV remote. Fire TV, although it has a minimalist design but it consumes a lot of battery-It just does. So, when I stumbled upon this feature of my remote, I was very happy as neither I had to pay for a set of batteries nor did I had to open the app on the phone and use it as my remote control (different tech but cool in its own way).


On my Samsung TV, this option comes as Anynet+. As I love working with different standards in technology, the mere thought of Anynet+ being some standard technology got me excited. However, to my disappointment, initial research was leading towards Anynet+ being a Samsung specific tech.


Little more investigation showed that it is the same technology (HDMI-CEC) branded by different TV companies by different names:

  • Anthem: CEC Control

  • Denon: CEC or HDMI Control

  • Funai, Emerson, Magnavox, Sylvania, and some Philips: Fun-Link

  • Hitachi: HDMI-CEC

  • Insignia: InLink

  • LG: SimpLink

  • Mitsubishi: NetCommand

  • Onkyo: RIHD

  • Panasonic: Viera Link, HDAVI Control, EZ-Sync

  • Philips: EasyLink

  • Pioneer: Kuro Link

  • Samsung: Anynet, Anynet+

  • Sharp: Aquos Link

  • Sony: Bravia Sync, Bravia Link

  • Toshiba: Regza Link, CE-Link

  • Vizio: CEC

So what is HDMI-CEC?

The "CEC" in HDMI-CEC stands for Consumer Electronics Control. It is an optional feature that allows control of multiple HDMI-connected devices from one remote control (such as a TV remote).

HDMI-CCE (Source)

What can HDMI-CEC do?


  • One-Touch Play/Record- When you start playback on your source device, it will switch the TV to the HDMI input that the device is connected to. 

  • Deck Control- This allows users, via a TV remote, to control playback features

  • One-Touch Record- If you have an HDMI-CEC enabled DVR or DVD recorder, you can start the recording process when you see a program of interest on your TV screen.

  • Device Menu Control- This allows your TV to control the menu system of another device. 

  • System Standby- This allows users to put several devices in standby mode using one remote control. 

How does HDMI-CEC work?

The basic technology of the CEC bus originated in Europe, on the SCART interface, where it’s been used with great success for many years. HDMI borrows and improves on the basic SCART technology, allowing AV products to discover and communicate with one another across a system. CEC makes possible global controls, which build on existing point-to-point E-DDC-based “plug & play” automation to minimize the number of IR remotes and keypresses required for the basic operation of a system. The CEC bus is a one-wire, “party line” that connects to ten (10) AV devices through standard HDMI cabling. The CEC protocol includes automatic mechanisms for physical address (topology) discovery, (product type based) logical addressing, arbitration, retransmission, broadcasting, and routing control. Message opcodes support both device-specific (e.g. set-top-box, DTV, and player) and general features (e.g. for power, signal routing, remote control pass-through, and on-screen display).


In every communication protocol, the following aspects are always covered:


  • How to send - Interpret (the actual protocol) Bit-level and Block-level Protocol When idle, pulls-up within CEC devices it lifts the CEC bus voltage to between 2.5 and 3.63 volts, CEC devices assert bits by pulling the bus down to between 0 and 0.6 volts. Bits are grouped into 10-bit headers and data blocks. Both header and data blocks include 8-bits of data along with EOM and ACK bits. The EOM bit signals the final block in a message. A ‘0’ indicates that one or more blocks follow and a ‘1’ indicates the message is complete. When a single follower provides an ACK to an initiator, it does so by “overriding” the output from the initiator (i.e. by pulling the bus to a logical ‘0’ while the Initiator sends a “passive” logical ‘1’). Broadcast messages have special rules for handling simultaneous ACKs from multiple devices. Here, the logic is reversed and a group of followers ACK by not “overriding” the initiator (i.e. by allowing the Initiator to send a “passive” logical). HDMI CEC messages are sent using frames. Each CEC frame consists of a start bit, a header block and possibly data blocks:

  • Where to send – Addressing & Broadcast CEC devices have both physical and logical addresses. Normally, upon each hotplug, each CEC source obtains a physical address by reading the EDID of the sink it is attached to. The physical address of each CEC device is expressed as four numbers and indicates where it is relative to the “root” display, whose address is always fixed at 0.0.0.0. Each CEC device also obtains a logical address - reflecting its product type - by negotiating with other CEC devices in the system. For example, the first STB in the system is always given the logical address 3.

  • What if others also want to say at the same time - Collision/Arbitration Since the CEC bus is a single wire, bus arbitration is very important. The CEC specification calls for a signal-free time before sending it. To allow other devices a chance to send, the time for a current initiator to send another frame is longer than that of a new initiator that wants to send a frame, and signal-free times for retransmissions are the shortest. If multiple devices try to send a message at the same time, a priority scheme is used to give a single initiator precedence.

  • What if they want to say something back - For two-way control – Bidirectional Communication is always between an initiator and one (or more) follower(s). Both initiator and follower(s) can assert bits. Initiator-asserted bits provide data, while follower-initiated bits provide acknowledgment. Bit-level communication is very slow by modern bus standards - with bit rates of less than 500 bits/second. Messages begin with one long start bit and are immediately followed by several shorter data bits.

  • What if not received - Reliability – Retransmission Frame transmissions play a key part in providing reliable communication. If there happen to any bus error or a frame error in a sense that it goes unacknowledged, then initiators get a sense of the situation and they may retransmit up to five times. It is also observed that when there is a hold up of ACKs by the destination devices, initiators get to work and retransmit.


Simple looking things are not so simple. Technology standards are designed for scalability, designed for comfort, designed for the future. But can we say our homes are future-ready? What is the future of Remote Control? Alexa, Google Assistant, Or Jarvis.


References:

https://www.lifewire.com/audio-return-channel-1846845

https://www.quantumdata.com/pdf/CEC_White_Paper.pdf


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