High-Definition Multimedia Interface, Consumer Electronics Control (Hdmi-Cec); Introduction; Frame Description; Figure 1. Cec Frame Format - ST STM32F100 Series Application Note

AN3127

High-definition multimedia interface, consumer electronics control (HDMI-CEC)

1 High-definition multimedia interface, consumer
electronics control (HDMI-CEC)
1.1

Introduction

Consumer electronics control (CEC) is the appendix supplement 1 to the HDMI (high-
definition multimedia interface) standard.
It is a protocol that provides high-level control functions between all of the various
audiovisual products in a given environment. It is specified to operate at low speeds with
minimum processing and memory overhead.
For more details, refer to the high-definition multimedia interface specification available from
www.hdmi.org.
1.2

Frame description

The CEC bus is a single-wire protocol that can connect up to 10 audiovisual devices through
standard HDMI cabling.
All transactions on the CEC line consist of an initiator and one or more followers. The
initiator is responsible for sending the message structure and the data. The follower is the
recipient of any data and is responsible for setting any acknowledgement bits.
A message is conveyed in a single frame that consists of a start bit followed by a header
block and, optionally, an opcode and a variable number of operand blocks.
CEC frame format.
Figure 1.
Figure 2.
CEC frame format
10 bits
Start bit Header block
Example of Header block:
Initiator address = 0x6
Destination address = 0xD
Header block
0 1 1 0 1 1 0 1
Initiator Destination
Message structure
Doc ID 16896 Rev 2
10 bits
Data bock 1
Example of Data block:
Data = 0xE5
1 1 1 0 0 1 0 1
0 -
Data
EOM ACK
Figure 1
10 bits
Data block n
Data block
0 -
EOM ACK
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