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Introduction to CEC Messaging: Quick Facts & Benefits

Learn about Consumer Electronics Control (CEC), its history, benefits, messaging types, device control, and more. Understand how CEC simplifies the operation of HDMI systems and enhances user experience.

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Introduction to CEC Messaging: Quick Facts & Benefits

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  1. 2008 Developers Conference Taipei, Taiwan

  2. An Introduction to Consumer Electronics Control (CEC) Quantum Data, Inc.

  3. What is CEC? – Quick Facts • CEC stands for Consumer Electronics Control. • It’s a one-wire bus (pin 13) that “snakes” through an HDMI system - allowing products to pass messages to one another. • CEC runs at approx. 400Hz, so including flow control bits and idle timing requirements on the line, it can send approximately 30 bytes each second. • Commands need to be very efficient.

  4. CEC: A Bit of History In Europe, there was an analog predecessor to HDMI known as the SCART interface. Like HDMI, SCART carried audio and video signals through one cable. The SCART cable had a one-wire bus for controlling a home theater system. This was branded as AV.link by Philips, among others. This bus supported one touch play, standby, etc.

  5. How To Find CEC Devices • CEC is available in many HDMI products today! • Limited multi-vendor interoperability.

  6. What is the benefit of CEC? • Today’s HDMI systems are comprised of separate components (digital set top boxes, audio receivers/amps, a DVD player, etc.), which are not always easy to configure & operate. • The general public has difficulty with the how/when/why to set up these devices in order to use them. The more devices, the more complex is the setup. • CEC is a solution to this problem! • CEC uses signal routing to allow devices to be configured across a system - rather than just point-to-point. Examples are one touch play and one touch record which greatly simplify the user experience.

  7. CEC Messaging

  8. CEC Messaging – Quick Facts CEC messages generally consist of two functional categories: Request – asking another device(s) to take action or to give information (e.g. asking a device to play, go into standby, switch sources, or request a device’s physical address). Informative – status messages and messages describing where a devices is in a network (e.g. report physical address, report vendor ID). CEC messages can also be grouped in terms of the intended target device: Directed Message - sent to a single CEC device. Broadcast - sent to all devices in the CEC network. CEC messages can be up to 16 blocks total (including the header and opcode blocks). If they were longer, they would impede access to the CEC bus due to the speed of the bus. (Sending 16 blocks successfully takes about 0.4s). The shortest message that can be sent is the polling message, which is simply a start bit followed by a header block. Devices must respond to a message in 1 second or less, but the desired response time is 200 msec.

  9. CEC Messaging – Blocks and Frames • A CEC message block includes the 8 data bits as well as two extra bits: • End of message – set to 0 for every block except the final block of the message where it is set to 1. • Acknowledgement (ACK) – set to 1 for every block. CEC Data Block CEC Header Block End of Message Information Bits Logical Address of Initiator Logical Address of Destination End of Message Acknowledgment Acknowledgment Example Messages: Image View On – 40 04 Routing Change - 5F 80 13 00 CEC Frame Optional Data Blocks Header Block Start Bit

  10. CEC at Work

  11. CEC at Work – One Touch Play Request Active Source (0F 85) Active Source (4F 82 11 00) Image View On (40 04) DVD DTV Active Source (4F 82 11 00) Active Source (4F 82 11 00) DVD ALL 01 00:00:11.01 00:00:00.00 PLAYER1->TV CEC CEC IMAGE VIEW ON 02 00:00:11.07 00:00:00.60 PLAYER1->ALL CEC CEC ACTIVE SOURCE 03 00:00:12.21 00:00:01.60 AUDIO->ALL CEC CEC REQUEST ACTIVE SRC Request Active Source (5F 85) Request Active Source (5F 85) 04 00:00:18.41 00:00:06.20 PLAYER1->ALL CEC CEC ACTIVE SOURCE 05 00:00:12.21 00:00:01.60 TV->ALL CEC CEC REQUEST ACTIVE SRC 06 00:00:18.41 00:00:06.20 PLAYER1->ALL CEC CEC ACTIVE SOURCE DVD AVR DTV DTV DVD ALL DTV ALL AVR DVD ALL DVD Game System STB-DVR Device functions, actions, message simulation only, 3 ports AVR

  12. CEC at Work – One Touch Play Set Stream Path (03 86 13 00) Image View On (30 04) STB-DVR DTV Active Source (3F 82 13 00) 01 00:00:11.01 00:00:00.00 TUNER->TV CEC CEC IMAGE VIEW ON 02 00:00:11.07 00:00:00.60 TV->TUNER CEC CEC SET STREAM PATH 03 00:00:12.21 00:00:01.60 TUNER->ALL CEC CEC ACTIVE SOURCE STB-DVR ALL DTV DTV Remote Ch. 2 Ch. 3 Ch. 4 AVR DVD Game System STB-DVR

  13. CEC at Work – Device Menu Control Ch. 2 Ch. 3 Ch. 4 User Control Released (03 45 XX) Menu Request (Activate) (03 8D 00) Image View On (40 04) STB-DVR DTV STB-DVR DTV Menu Status (Activate) (30 8E 00) Active Source (4F 82 11 00) Menu Request (Deactivate) (03 8D 01) 01 00:00:11.01 00:00:00.00 PLAYER1->TV CEC CEC IMAGE VIEW ON STB-DVR ALL 02 00:00:11.07 00:00:00.60 PLAYER1->ALL CEC CEC ACTIVE SOURCE 03 00:00:11.01 00:00:00.00 TV->TUNER CEC CEC MENU REQUEST 04 00:00:11.07 00:00:00.60 TUNER->TV CEC CEC MENU STATUS User Control Pressed (03 44 XX) Menu Status (Deactivate) (30 8E 01) 05 00:00:12.21 00:00:01.60 TV->TUNER CEC CEC USER CNTL PRESSED 06 00:00:18.41 00:00:06.20 TV->TUNER CEC CEC USER CNTL RELEASED 07 00:00:19.00 00:00:00.59 TUNER->TV CEC CEC MENU REQUEST 08 00:00:19.59 00:00:00.50 TV->TUNER CEC CEC MENU STATUS DTVRemote DTV AVR DVD Game System STB-DVR

  14. CEC at Work: One Touch Record Record TV Screen (10 0F) STB-DVR DTV Record ON [Digital Service ID] (01 09 02) 01 00:00:18.41 00:00:00.00 RECORDER->TV CEC CEC RECORD TV SCREEN 02 00:00:69.51 00:00:51.10 TV->RECORDER CEC CEC RECORD ON 03 00:00:69.71 00:00:00.20 RECORDER->TV CEC CEC RECORD STATUS DTV Record Status [Recording Digital Service] (10 0A 02) Recording AVR DVD Game System STB-DVR

  15. CEC at Work – Deck Control Deck Status [Skip Forward] (40 1B 17) Deck Status [Play] (40 1B 11) Deck Control [Skip Forward] (04 42 01) Play [Forward] (04 41 24) DTV DVD 01 00:00:11.01 00:00:00.00 TV->PLAYER CEC CEC PLAY FORWARD 02 00:00:11.07 00:00:00.60 PLAYER->TV CEC CEC PLAY STATUS 03 00:00:11.01 00:00:00.00 TV->PLAYER CEC CEC SKIP FORWARD 04 00:00:11.07 00:00:00.60 PLAYER->TV CEC CEC SKIP STATUS DTV DTV Remote AVR DVD Game System STB-DVR

  16. CEC at Work - Shutdown Standby (0F 36) DTV ALL 01 00:00:11.01 00:00:00.00 TV->*ALL* CEC CEC STANDBY DTV AVR DVD Game System STB-DVR

  17. CEC Addressing

  18. CEC Addressing CEC assumes that all AV source products in a system are directly orindirectly connected to a “root” display (DTV). HDMI connections form an upside-down tree, with a display as the “root”, switches as “branches”, andvarious source products as “leaf” nodes. There are two types of addressing: Logical Physical

  19. Logical Addressing Logical addressing is what CEC uses to identify a specific instance of a specific device type. When messages are sent over CEC, the logical address identifies both the sender (“Initiator”) and intended receiver (“Follower”) of the message. Logical addressing is done with nybbles (4-bit numbers, allowing for addresses from 0-15). Because of this, the header blocks are simply in “to, from” format – the first four bits sent are the address of the initiator (or sender), while the latter four bits are the follower’s (receiver’s) address. CEC Header Block Logical Address of Initiator Logical Address of Follower End of Message Acknowledgment

  20. Logical Addressing (continued) Logical addresses are split among device types: 0 is a TV 1,2 & 9 are recorders (HDD, DVD, BD, etc.) 3,6,7 & 10 are tuner devices (i.e. set-top boxes) 4,8 & 11 are players (DVD, VCR, Blu-Ray, etc.) 5 is an audio system 12 & 13 are reserved 14 is a wild-card 15 means “Unregistered” if it’s the initiator address, “Broadcast” if it’s the follower address.

  21. Physical Addressing Physical addressing describes the topology, i.e. what devices are between the CEC device and the TV, and through what inputs it is connected. Physical addressing is a required feature for ALL HDMI devices (regardless of whether or not they support CEC), and is essential for routing control, among other things.

  22. Physical Addressing Description A TV (that does not have HDMI outputs) will use physical address [0.0.0.0]. Any device with an HDMI output will have an address that contains at least one non-zero number, which is grabbed from the HDMI vendor specific data block (VSDB) of the sink device’s EDID. Devices with both a source and a sink must read the physical address from the EDID of the sink device that it is attached to, and configure its own EDIDs on its sink ports so that they contain the proper physical addresses.

  23. CEC Addressing – Physical Addressing DTV PA 0000 1000 PA 1000 AVR 1100 1300 1200 DVD Game System STB-DVR PA 1100 PA 1200 PA 1300

  24. Physical Addressing – VSDB of EDID 1100

  25. CEC Addressing – Logical Addressing DTV ALL Report Physical Address (0F 84 00 00) Report Physical Address (8F 84 12 00) Report Physical Address (4F 84 11 00) Report Physical Address (5F 84 10 00) 01 00:00:10:0174 00:00:01:0100 TV->*ALL* CEC CEC REPORT PHYSICAL ADDRESS Game System AVR Unregistered DVD ALL AVR ALL ALL 02 00:00:11.0274 00:00:00:0060 UNREG->AUDIO CEC CEC CEC PING - NACK 03 00:00:11:0639 00:00:00:1000 AUDIO->*ALL* CEC CEC REPORT PHYSICAL ADDRESS 04 00:00:11:1639 00:00:00:0100 UNREG->PLAYER1 CEC CEC CEC PING - NACK 05 00:00:11:1739 00:00:00:0251 PLAYER1->*ALL* CEC CEC REPORT PHYSICAL ADDRESS 06 00:00:11:1990 00:00:00:0028 UNREG->PLAYER1 CEC CEC CEC PING 07 00:00:11:2018 00:00:00:0122 UNREG->PLAYER2 CEC CEC CEC PING - NACK 08 00:00:11:2140 00:00:00:0100 PLAYER2->*ALL* CEC CEC REPORT PHYSICAL ADDRESS DVD Unregistered LA 0 PA 0000 DTV Game System Unregistered LA 05 PA 1000 LA 04 LA 08 LA 04 AVR PA 1200 LA 1100 STB-DVR Game System DVD Polling Message (F4) Polling Message (F5) Acknowledged Polling Message (F8) Polling Message (F4)

  26. CEC Addressing – Logical Addressing STB-DVR Unregistered Report Physical Address (3F 84 13 00) Report Physical Address (1F 84 13 00) 01 00:00:10:0174 00:00:01:0100 TV->ALL CEC CEC REPORT PHYSICAL ADDRESS STB-DVR STB-DVR ALL ALL 02 00:00:11.0274 00:00:00:0060 UNREG->AUDIO CEC CEC CEC PING - NACK 03 00:00:11:0639 00:00:00:1000 AUDIO->ALL CEC CEC REPORT PHYSICAL ADDRESS 04 00:00:11:1639 00:00:00:0100 UNREG->PLAYER1 CEC CEC CEC PING - NACK STB-DVR Unregistered 05 00:00:11:1739 00:00:00:0251 PLAYER1->ALL CEC CEC REPORT PHYSICAL ADDRESS 06 00:00:11:1990 00:00:00:0028 UNREG->PLAYER1 CEC CEC CEC PING 07 00:00:11:2018 00:00:00:0112 UNREG->PLAYER2 CEC CEC CEC PING - NACK 08 00:00:11:2140 00:00:00:0100 PLAYER2->ALL CEC CEC REPORT PHYSICAL ADDRESS 09 00:00:11:2230 00:00:00:0600 UNREG->TUNER CEC CEC CEC PING - NACK 10 00:00:11:2830 00:00:00:0164 TUNER->ALL CEC CEC REPORT PHYSICAL ADDRESS DTV: PA 000 LA 0 AVR: PA 1000 LA 05 DVD: PA 1100 LA 04 Game System: PA 12 00 LA 08 STB-DVR: PA 1300 LA 03/LA 01 11 00:00:11:2994 00:00:00:0600 UNREG->RECORD CEC CEC CEC PING - NACK 12 00:00:11:3594 00:00:00:0000 RECORD->ALL CEC CEC REPORT PHYSICAL ADDRESS LA 0 PA 0000 DTV DTV LA 05 PA 1000 LA 08 LA 01 LA 03 AVR PA 1200 PA 1300 STB-DVR Game System DVD LA 04 Polling Message (F1) Polling Message (F3) LA 1100

  27. CEC Addressing – Sample Network

  28. CEC Physical Layer

  29. Physical Information CEC is pin 13 on the HDMI cable. It shares a common ground with DDC. CEC idles in a high-impedance state (the line shows a voltage between +2.5 and +3.63V). During a message, the line will be pulled down to between 0 and +0.6V (“low-impedance”).

  30. Physical Information (continued) CEC supports nine devices on the bus simultaneously (potentially more if good cabling is used). The limitation is due to a network limit on capacitance of 7200pF (allowing for 100pF per device and 700pF per cable). However, there are only 15 valid CEC logical addresses, so having a limitation of nine devices would rarely be a problem in real-world applications. The CEC line is in use when there is a device pulling the line low. All timing is derived from the high to low transitions.

  31. Physical Information – Bit Timing Start Bits Logical “0” and “1”

  32. CEC Message Waveform • Max Rise Time = 250usecs • Max Fall Time = 50usecs

  33. CEC Bus Control

  34. CEC Bus Control - Retransmission Retransmission can occur for many reasons: A device could be holding the CEC bus low when the initiator expects it high, causing a bus error. A device sends a message and does not receive the expected acknowledgement. A device loses arbitration (retry). Retransmission should not occur if there is sufficient indication that the follower does not support the message being sent.

  35. CEC Bus Control - Acknowledgement • Directed messages • Intended for a single device • ACK is set as a “logical 1” • Set to “logical 0” by the follower to acknowledge • Broadcast messages • Intended for all devices • ACK is set as a “logical 1” • Must be kept as a “logical 1” by all devices • A “logical 0” is a NACK

  36. CEC Bus Control - Acknowledgement Image View On (30 04) Directed Message STB-DVR DTV 01 00:00:11.01 00:00:00.00 TUNER->TV CEC CEC IMAGE VIEW ON Pull down bus to Ack with “0’ bit 02 00:00:18.41 00:00:06.20 AUDIO->ALL CEC CEC REQUEST ACTIVE SRC STB-DVR DTV Request Active Source (5F 85) Request Active Source (5F 85) high low DTV 0.6 ms 1.5 ms Release bus Release bus to set Ack bit to “1” Broadcast Message STB-DVR DTV AVR AVR Do nothing to acknowledge ALL high low AVR 0.6 ms Release bus to setAck bit to “1” DVD Game System STB-DVR

  37. CEC Bus Control – No Acknowledgement Image View On (30 04) Directed Message STB-DVR DTV 01 00:00:11.01 00:00:00.00 TUNER->TV CEC CEC UNACKNOWLEDGED 02 00:00:18.41 00:00:06.20 AUDIO->ALL CEC CEC UNACKNOWLEDGED AVR DTV Request Active Source (5F 85) Request Active Source (5F 85) high low DTV 0.6 ms Release bus to set Ack bit to “1” Do nothing to Nack Broadcast Message STB-DVR DTV AVR Pull down to 0 to Nack STB-DVR DTV high low AVR 0.6 ms 1.5 ms Release bus Release bus to set Ack bit to “1” DVD Game System STB-DVR

  38. CEC Bus Control - Arbitration Since CEC is a single wire for all devices, it is sometimes the case that two devices want to use the CEC line at the same time. Arbitration check begins with leading edge of start bit and continues to end of initiator address. Priority given to the device with the lowest logical address. The TV (logical address 0) has priority over all other devices. If a device is already using the CEC line, the devices that would like to use it must wait until “signal free time” has been met (the device has stopped using the line for a defined length of time). At least 3 bit periods (7.2ms) in the case of a device trying to resend a message. At least 5 bit periods (12.0ms) for a new device wishing to send a message At least 7 bit periods (16.8ms) for the same device wishing to send a new message. Signal free time is defined from the START of the final bit being sent (the high to low transition).

  39. CEC Bus Control - Arbitration Image View On Image View On (40 04) Get Menu Language (04 91) Record TV Screen DVD DTV DVD Record TV Screen (01 0F) Record ON [Digital Service ID] (10 09 02) Active Source (4F 82 11 00) 01 00:00:11.01 00:00:00.00 PLAYER1->TV CEC CEC ERROR 02 00:00:11.07 00:00:00.60 TV->PLAYER1 CEC CEC GET MENU LANGUAGE 03 00:00:12.01 00:00:00.20 PLAYER1->TV CEC CEC IMAGE VIEW ON 04 00:00:12.21 00:00:01.60 PLAYER1->ALL CEC CEC ACTIVE SOURCE 05 00:00:18.41 00:00:06.20 TV->RECORDER CEC CEC UNACKNOWLEDGED Signal Free Time >/= 5 bit times (~ 12.0ms) New Message 06 00:00:18.49 00:00:06.11 TV->RECORDER CEC CEC RECORD TV SCREEN Record Status [Recording Digital Service] (01 0A 02) 07 00:00:69.51 00:00:51.10 RECORDER->TV CEC CEC RECORD ON 08 00:00:69.71 00:00:00.20 TV->RECORDER CEC CEC RECORD STATUS DTV DTV STB-DVR Signal Free Time >/= 3 bit times (~ 7.2ms) Retransmit AVR DVD Game System STB-DVR

  40. Verifying CEC Implementation

  41. Verifying the CEC Implementation Compliance testing In-house using compliance test tools Plugfests (CEA and ETSI) HDMI Authorized Test Centers Interoperability testing (multi-vendor) In-house Plugfests

  42. Verifying the CEC Implementation • Tools you will need • CEC debug tools used during development • CEC bus monitor • CEC compliance test application (Quantum Data Test Management Environment is the recommended test tool in the HDMI CTS) • Test fixtures

  43. CEC Debug Testing – Error Simulator Sample screen of CEC debug test application. Enables: • Simulation of acknowledgement failures • Simulation of arbitration failures • Ability to corrupt bits • Modify timing parameters (Quantum Data CEC Controller)

  44. CEC Debug Testing – Message Logger Sample screen of CEC Transaction logger: • Logs CEC trans- actions during compliance test • Logs CEC trans- actions during debug testing • Shows detailed timing • Shows acknow- ledgement and other errors (Quantum Data Auxiliary Channel Analyzer)

  45. CEC Compliance Testing – CDF Entry Sample of a CEC compliance test application showing CDF definition: • Enables importing CDF from comma separated value file for fast CDF definition • Enables definition of CDF parameters for new devices through GUI • Supports saving CDFs for later use (Quantum Data CEC Compliance Application)

  46. CEC Compliance Testing - Test Initiator Sample of a CEC compliance test application showing test execution: • Enables running of selective tests, or groups of tests • Online help for test setup • Tests run automati- cally without user interaction after test setup • Results provided on display interface • Comprehensive report for all tests that can printed or emailed. (Quantum Data CEC Compliance Application)

  47. For more information… • Quantum Data has prepared an educational whitepaper and a video on CEC that provides some further examples: http://www.quantumdata.com/

  48. Thank You… Presenter: Neal Kendall Technical consultant: Jeff Stenhouse Animation & Graphics: Robert Watson

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