Hdmi-Cec Functional Description; Hdmi-Cec Pin; Hdmi-Cec Block Diagram; Message Description - ST STM32G0 1 Series Reference Manual

HDMI-CEC controller (CEC)
39.3

HDMI-CEC functional description

39.3.1

HDMI-CEC pin

The CEC bus consists of a single bidirectional line that is used to transfer data in and out of
the device. It is connected to a +3.3 V supply voltage via a 27 kΩ pull-up resistor. The output
stage of the device must have an open-drain or open-collector to allow a wired-AND
connection.
The HDMI-CEC controller manages the CEC bidirectional line as an alternate function of a
standard GPIO, assuming that it is configured as alternate function open drain. The 27 kΩ
pull-up must be added externally to the microcontroller.
To not interfere with the CEC bus when the application power is removed, it is mandatory to
isolate the CEC pin from the bus in such conditions. This can be done by using a MOS
transistor, as shown on
Name
CEC
39.3.2

HDMI-CEC block diagram

Cortex
Core
HSI
LSE
39.3.3

Message description

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 acknowledgment 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.
1348/1390
Figure 414.

Table 242. HDMI pin

Signal type
Bidirectional

Figure 414. HDMI-CEC block diagram

CEC interrupt
CEC
ITF
AHB APB
RCC
CLK
32 kHz
CEC
Kernel
Event
Wake-int
control
RM0444 Rev 5
Two states:
– 1 = high impedance
– 0 = low impedance
A 27 kΩ resistor must be added externally.
STM32
HDMI_CEC
controller
27 kΩ
RX
TX CEC
PAD
Remarks
3.3V
3.3V
G
Remote
CEC
D
CEC line S
device
RM0444
MSv35920V2