DS90UB949-Q1: Trigger of HPD H -> L

Atsushi Hirai

Hi team,

In previous post, I drew below image but, it seems inaccurate. (But it may work as expected because HPD low period masks the GPIO0 signal)

When the customer checked the HPD signal, it went to low when he connect FPD Link cable and return to high automatically.

According to the datasheet, the Low to High transition means HDMI sink(Ser) is ready.

What is the trigger of High to Low transition? Is it FPD Link lock?

Best Regards,

over 4 years ago

0 Ben Dattilo over 4 years ago

TI__Mastermind 25765 points

Hello,

If the UB949 is no longer connected and/or able to receive an HDMI from the source, HPD will transition from H to L. HPD will stay low until the device is ready to receive signals from the source, then it will be pulled up to 5V and transition to back to H.

Regards,

Ben

0 Atsushi Hirai over 4 years ago in reply to Ben Dattilo

TI__Expert 5670 points

Ben-san,

It's difficult to understand. Could you draw an example timing diagram?

Regards,

0 Ben Dattilo over 4 years ago in reply to Atsushi Hirai

TI__Mastermind 25765 points

Atsushi-san,

Here is a diagram showing an example of sequence of events. Note: this diagram shows a basic example of the sequence of events regarding HPD and does not show actual timing.

Regards,

Ben

0 Atsushi Hirai over 4 years ago in reply to Ben Dattilo

TI__Expert 5670 points

Ben-san,

Originally I also thought like your answer but, actual behavior is different.

No FPD connection makes High.

Once FPD cable is connected, it goes Low

Around 150ms later, it returns to High automatically.

Could you check the actual behavior and trigger signal of HPD High to Low?

Best Regards,

+1 Ben Dattilo over 4 years ago in reply to Atsushi Hirai

TI__Mastermind 25765 points

Hello Atsushi-san,

The HPD will only be asserted if there is a lock between the 949 device and a downstream serializer. If HPD is indeed high when not locked to a deserializer, it may be that HPD is being forced high, then is pulled low when connected and pulled back high when ready to receive a signal. Forcing HPD has been done in some applications.

The latter part of your description:

Atsushi Hirai said:
Once FPD cable is connected, it goes Low

Around 150ms later, it returns to High automatically.

Is normal behavior, as I described in my previous reply.

Regards,

Ben

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DS90UB949-Q1: Trigger of HPD H -> L