Trion T20 BGA256 Query

[RetroHQ]

Hi! I have a query on the Trion BGA if you don’t mind. As you are driving the DVI signals directly, what kind of maximum dot clock have you been able to achieve like this? And are you going through something like the PTN3366 to convert from ac coupled LVDS to CML? And have you also tried using the 5:1 gearing on the LVDS serialiser to give you just 2x dot clock in terms of actual output clocking?

I’m about to try this with the T20 for a small single board computer project and am just curious as to your experience! I’ve driven DVI directly with just ac coupled LVDS successfully before, so the implementation side of things I already have proven, I’m curious more on the specifics of the T20. I’m a big fan of Trion chips, but they are certainly not ideal for trying to drive DVI.

[randyrossi]

29Mhz is my max. I'm using SN65CML's to convert LVDS to CML. I also had to add a load switch to deal with 5V backfeeding from the HDMI connector that can power the FPGA. I'm not using the LVDS serializer. The serialization is driven by a 10x dot clock. I did try but I can't remember the reason the LVDS serializers didn't work for me. I think with ac coupled LVDS, you might be able to get around 16mhz. So you can probably do 640x480. The Tiron chips are definitely not ideal for DVI. I'm amazed it works, really.

[RetroHQ]

Fantastic, thank-you for the response! The PTN3366 takes care of the backfeeding of current and also level shifting on the I2C lines for querying modes, too, it looks like quite a useful (and cheap) part. The LVDS side of the T20 can, apparently, be clocked up to 800Mhz, but I guess ac coupling factor is limiting. :(

[RetroHQ]

Just as a FYI, I've finally built up a test board and I can output 720P via a PTN3366 using 5x serialisation just fine.