TUSB546A-DCI: HDMI Alt Mode - TPS65987D without DDC

Benjamin

I would start with this app note as a design reference, https://www.ti.com/lit/an/slla333/slla333.pdf for question 1 and 2. 

For question 1, the PD controller will detect the connection and orientation of a sink device through the CC1 and CC2. The TUSB546 HPD is used as a power management feature that can enable/disable its output when the TUSB546 is being configured in the DP Alt Mode.

For question 2, You can use the PD controller to control the FLIP depends on the CC1/2 condition. But if the PD controller can't handle the DDC communication, then you need another piece of hardware to handle the SBU/DDC communication.

I think the easiest solution is to find a PD controller that supports HDMI Alt Mode over Type-C or go with question #3.

Thanks

David 

Hi David,

Thanks very much for your reply on the above points.

I think the best solution indeed will be searching for a dedicated PD controller with HDMI alt mode, or doing the conversion events as you suggested.

Out of interest, am I correct in saying that the TPS65987D will not be able to communicate any GPIO events listed in the document here with the above application in any manner? I would imagine that some events like cable flip (i.e Port 0 Cable Orientation Event GPIO), PD contract related registers & DFP event detection reads would still work fine over the CC lines, however registers relating to detection of any HDMI sink device would not work properly. How does the TPS65897D know when a HDMI sink device is connected and to pass the lines through the muxer from sink to source?

In particular, can the CTL0/CTL1 pins of the TUSB546 still be controlled from the TPS65987D in GPIO mode? If not, could I just tie these pins with pull resistors to achieve desired function? I don’t plan on implementing high speed muxing of USB 3.1 signals on my board. 

www.ti.com/.../slvae11a.pdf

Kind regards,
Benjamin

Benjamin

For this question, 'Out of interest, am I correct in saying that the TPS65987D will not be able to communicate any GPIO events listed in the document here with the above application in any manner? I would imagine that some events like cable flip (i.e Port 0 Cable Orientation Event GPIO), PD contract related registers & DFP event detection reads would still work fine over the CC lines, however registers relating to detection of any HDMI sink device would not work properly. ', I am asking my co-worker in the PD controller team to provide input.

Thanks

David

Thanks Dave

Hi Dave,

Did your colleague get back to you on the above GPIO event question? 

Kind regards
Benjamin

Benjamin

Their response will be posted in this ticket.

Thanks

David

Thanks Dave,

One question I wanted to ask is how the PD controller knows when an alternate mode sink device is connected to the USB-C receptacle. In DisplayPort, I think this is handled over the CC lines via a 3v3 HPD. How is this handled with HDMI? The spec says to connect the sink HPD to the USB-C connector SBU1 pin, but the app note you linked above says to connect the HPD directly to the PD controller and MUX, which I’m not sure how that works because it’s a 5V logic signal. 

I assume both USB and HDMI sink devices (i.e a display monitor) have pull-downs on the other end, so the PD controller knows a sink device is connected. 

Then, how does the PD controller know the difference between an alternate mode device (i.e a monitor) and say, a USB 2.0/3.0/3.1 peripheral? 
In GPIO mode, how does the PD controller know to change the status of CTL1, CTL0 and flip pins to enter and exit alternate mode, assuming these are the pins that control them. 

The reason I say this is because Adam here made it seem like that the PD controller has no way of knowing if a HDMI is connected in a different thread I read.

Kind regards,
Benjamin

Benjamin

The connection detection or discovery is handled by the USB Type-C to HDMI Cable Adapter.

The Cable Adapter contains logic circuit to implement SOP communication of USB PD and support discovery. 

• The HDMI DDC and CEC using the USB Type-C CC communication signaling when operating in HDMI Alt Mode.
• The Utility and HPD are transmitted directly through pin A8 and B8 of the Type-C connector when operating in HDMI Alt Mode. They need to be switched off until the transition to HDMI Alt Mode.

Thanks

David

Hi David, 

Thanks for the informative response, very much appreciate your help. 

Hopefully my last question here… Is the TPS65897D able to detect an alternate mode sink device for HDMI or only for DisplayPort? I assume if the detection is done over the CC wire there must be some register I can read back from the TPS65897D to detect a HDMI sink device? 

Have a great weekend.
Ben

Dave,

I also wanted to ask if TI have a HDMI 2.0 to DP 1.2/1.4 converter IC that I could use alongside the TPS65897D. Think it's best to go this way rather than use the less common HDMI Alternate Mode standard after all. 

Ben