Controlling an HDMI Transmitter

I plan to use the NXP TDA19988BHN HDMI transmitter in a design. I will be driving it with an FPGA which produces 8-bit RGB video output. It is reverse-engineered from a design which fed an Analog Devices ADV7125KSTZ140 video DAC, and has been proven to work in that design. My goal is to take the 8-bit (actually, 6-bit since the two LSBs are grounded) RGB output from the FPGA and use that as the input to the TDA19988. I do not require audio, so I have left that off the schematic.

My current schematic is attached in PDF format. I left off the majority of the design as much of it is not particularly applicable to this question, and just adds a lot of unnecessary information. The sheet I attached is only showing the TDA19988 connections.

Would someone here please review this schematic and let me now if I have missed anything crucial? I cannot seem to find much documentation on the TDA19988 other than the datasheet, so I'm hoping someone here has more experience with HDMI transmitters in general and is able to identify what might be missing from my design.

Many thanks,
Matt

I did spend some time looking at this...it is not clear why I did, but I did. What I essentially did was to compare your design with **broken link removed** [linked from here] and I had the data sheet out while doing so. I understand you are not doing audio.

No, I found no gross errors, but I am hoping that you will address a few questions...

You are using pull down resistors for the configurable I2C address lines rather than straight connections to ground - are you just being extra careful/concientious/best practices?

You are not going to support CEC and have that line nc. I read something where CEC and I2C communications are or can be related in the sense that an external device can grab them or some such thing...is just leaving that line nc ok?

One thing I did notice that could, potentially be of some concern is that you have the TX lines going straight through to the HDMI connector while the other design uses some kind of hi-speed esd diodes [ the IP4283C210-TT] - is this going to be a noise issue?

I was also reading that NXP has not publicized all of the I2C registers - a few folks complained about that and one said that you had to sign an NDA first - is that true? Do you know?

DrG said:

hi-speed esd diodes

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I have always used protection diodes. (low capacitance diodes)

Hello, thank you very much for the response. Here are my answers to your questions:

You are using pull down resistors for the configurable I2C address lines rather than straight connections to ground - are you just being extra careful/concientious/best practices?

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This is mostly to follow best practices. I generally try not to connect inputs or outputs directly to a rail, even if I never plan to change them. I only used 4.53k resistors (rather than a lower value) because I already use them in multiple places in the design.

You are not going to support CEC and have that line nc. I read something where CEC and I2C communications are or can be related in the sense that an external device can grab them or some such thing...is just leaving that line nc ok?

Click to expand...

CEC is a bidirectional signal that allows communication over a home appliance network. As far as I can tell it does not need to be connected, but this is one of the questions I had and am hoping someone can confirm this assumption.

One thing I did notice that could, potentially be of some concern is that you have the TX lines going straight through to the HDMI connector while the other design uses some kind of hi-speed esd diodes [ the IP4283C210-TT] - is this going to be a noise issue?

Click to expand...

As a matter of fact, I do have ESD protection on the HDMI connections. The devices are actually shown on a different sheet of the schematic with the HDMI connector.

I was also reading that NXP has not publicized all of the I2C registers - a few folks complained about that and one said that you had to sign an NDA first - is that true? Do you know?

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I saw the same post you did mentioning this concern, and I decided this will just be a bridge I'll have to cross when I come to it. I have no problem signing an NDA if need be.

DerStrom8 said:

CEC is a bidirectional signal that allows communication over a home appliance network. As far as I can tell it does not need to be connected, but this is one of the questions I had and am hoping someone can confirm this assumption.

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If it's any help?, CEC was created jointly by Sony and Panasonic (and has been adopted as the standard, under various individual manufacturer names), AFTER the original HDMI was released - so the first units to use HDMI didn't support CEC at all, as it didn't exist.

DerStrom8 said:

I plan to use the NXP TDA19988BHN HDMI transmitter in a design./--/
Matt

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Just curious if there is any update on this - did it all work the way that you anticipated?

DrG said:

Just curious if there is any update on this - did it all work the way that you anticipated?

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Hi DrG, sorry for the delay. I don't get much time to browse the forums these days.

I ended up dropping the TDA19988 due to lack of documentation and instead opted for the Texas Instruments TFP410. This is the part used for HDMI on boards like the Beaglebone and other well-known designs, and the documentation and support is far more comprehensive. I am still working on the firmware to configure the device but I feel I am making good progress. I will try to remember to post an update once I get things working.