Hardware environment
AN3127
Doc ID 16896 Rev 2
2 Hardware
environment
To be fully compliant with the stringent HDMI 1.3a specification, specially when the CEC
device is in the power-off state, a fully integrated ESD protection should be added externally
to the STM32F100xx device. For that purpose, the HDMI2C1-5DIJ ensures level-shifting
and serves as the signal booster for control links of HDMI 1.3 transmitters. The HDMI2C1-
5DIJ is a bidirectional isolation buffer, integrating hysteresis and signal boosters for
maximum system robustness and signal integrity.
In addition to this circuit, the 27 k
Ω
pull-up resistor on the CEC line should be externally
connected to the STM32F100xx.
With these few hardware additions, the STM32F100xx CEC solution (CEC peripheral plus
ESD protection circuit) is fully compliant with the HDMI 1.3 standard.
The solution is already implemented on Value line evaluation boards. Two HDMI connectors
are available for each Value line evaluation board (CN15, CN16 for STM32100B-EVAL and
CN2, CN3 for STM32100E-EVAL). The CEC, SCL, SDA and HPD signals are supported
and connected to STM32F100xx through HDMI2C1-5DIJ.
The external hardware component is only needed when the CEC power-off state is needed
in the application. If the power-off state is not needed, you can directly connect the
STM32F100xx CEC line to the CEC bus.
2.1 HDMI
connector
Only a vendor-approved, HDMI connector should be used. The list of approved HDMI
connectors is available from the HDMI site (
www.hdmi.org
).
The differential impedance of this connector should be equal to 100
Ω
±15%. This can be
checked by using time domain reflectometry (TDR) equipment.
Figure 10.
HDMI cable