CEC Interface




Consumer Electronics Control Interface

The Consumer Electronics Control [CEC] bus.
CEC is a 1-wire bus running on the HDMI interface providing automatic control in HDMI-interfaced systems.
The CEC interface pins shows up on pin 13 of the HDMI connector interface, found below.
CEC will connect up to 10 Audio Visual [AV] devices.





Electrical Characteristics
When idle, CEC devices lift 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. All devices monitor the logical state of the bus by comparing bus voltage with a state-dependent threshold, which provides approximately 400 millivolts of hysteresis. Rise and fall times may be purposely slowed to avoid ringing. Signal rise and fall times only need to be less than 250 and 50 microseconds, respectively.
Bit-level Protocol
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 a number of shorter data bits. Start bits last 4.5 milliseconds and have a low period of 3.7 milliseconds Data bits only last for 2.4 milliseconds and have a low period that depends on the logical data value being communicated. Here, logical zero bits have a longer low state than logical one bits
Block-level Protocol
Bits are grouped into 10-bit header 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 '1').





HDMI-to-HDMI Cable
HDMI Cable

HDMI Connector Pinout
Pin Number Signal name Pin Number Signal name
1 TMDS Data 2+ 20 SHELL
2 TMDS Data 2 Shield 19 Hot Plug Detect
3 TMDS Data 2- 18 +5V Power
4 TMDS Data 1+ 17 Ground
5 TMDS Data 1 Shield 16 DDC Data
6 TMDS Data 1- 15 DDC Clock
7 TMDS Data 0+ 14 No Connect
8 TMDS Data 0 Shield 13 CEC
9 TMDS Data 0- 12 TMDS Clock-
10 TMDS Clock+ 11 TMDS Clock Shield


HDMI Connector Manufacturers

ACON {HDMI A Type}

Leoco {High Definition Media Input, HDMI Socket, HDMI Plug}

Molex {HDMI Connector Manufacturer}

Tyco Electronics {HDMI Connectors}





Computer Video Monitor Information Pages

DFP [Digital Flat Panel] page for additional info and connector pinout descriptions
EVC [Enhanced Video Connector] page for additional info and connector pin-out descriptions
EGA [Enhanced Graphics Adapter] Which dates back to 1984.
XGA [eXtender Graphics Adapter] Also an out-dated interface from 1990.
VGA [Video Graphics Adapter] Which is the original 'VGA' interface standard.
SVGA [Super Video Graphics Adapter] Which is the current 'VGA' standard.
PC Video Buses

Additional information;

NTSC [National Television System Committee] is used in US [and Japan]
PAL [Phase Alternation by Line] is used outside the US
.... M-PAL [Phase Alternation by Line] is used outside the US [Brazil]
.... N-PAL [Phase Alternation by Line] is used outside the US
SECAM [Sequential Color with Memory] is used outside the US [France/Russia/Africa]


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Modified 6/13/15
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