AN3127
High-definition multimedia interface, consumer electronics control (HDMI-CEC)
Doc ID 16896 Rev 2
7/36
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.
shows a
CEC frame format.
Figure 1.
CEC frame format
Figure 2.
Message structure
S
t
a
rt
b
it
0
1
1
0
1
1
0 1
0
-
EOM
ACK
Initiator
De
s
tination
Header block
He
a
der
b
lock
D
a
t
a
b
ock 1
D
a
t
a
b
lock n
10
b
it
s
10
b
it
s
10
b
it
s
Initi
a
tor
a
ddre
ss
= 0x6
De
s
tin
a
tion
a
ddre
ss
= 0xD
Ex
a
mple of He
a
der
b
lock:
1
1
1
0
0
1
0 1
0
-
EOM
ACK
Data
Data block
D
a
t
a
= 0xE5
Ex
a
mple of D
a
t
a
b
lock:
a
i159
3
1
3TART
HIGH
(EADER
/PCODE
/PERAND
/PERAND
TOOPERANDS
HIGH
IMPEDANCE
BIT
IMPEDANCE
AI