HDMI interface doubt

[ku637]

Hello,

Any body can suggest me how the HPD and CEC pins function in HDMI interface.

I want to correctly interface these signals to my SoC board

Is HPD ( hot plug detect ) being supplied by the external device ? 5V will appear on HPD line when external device is connected.is this understanding correct.

CEC pin in my understanding is a communication line, but can it be treated like an open drain manner so that we can pull it up to my SoC use voltage

 

[KlausST]

HI,

what I did:

* Internet search "HDMI Interface specification"
* this leads me to: wikipedia "High Definition Multimedia Interface"
* in Wikipedia I used the link to CEC "Consumer Electronics Control"
* there you have a lot of reference documents like: " Designing CEC into your next HDMI Product "

What else do you need?

it took about 15 seconds....

Klaus

 

[ku637]

Hi KlausST,

Thank you for the comment. I had actually referred that document before posting the query here..

That document says CEC devices have internal pull ups but not sure if that mandates inside my board too or relying on pull up inside display is ok..

Electrical Characteristics
When idle, pull-ups within 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 de-
vices 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. Maximum leakage current is limited to 1.8
microamps to prevent devices from affecting the CEC bus, when they are disconnected
from the power company. Since the CEC bus can include ten 100pF devices and nine
700pF cables, the maximum bus capacitance is 7200pF.

Any clarity on that will be helpful

 

[KlausST]

Hi,

I don´t know how your SOC board is related to a display or a PCB..so I can´t answer about this-

"Pull-ups wihtin CEC devices" should be clear.
The rest is an active device for pulling down.
It may be a bjt in open collector, or a MOSFET in open drain, or a totem pole with series diode...I think it does not matter as long as it fullfills the timing and level specifications.


Klaus

added: for further discussion a sketch that explains your situiation would be helpful.