[Oberon] HDMI question

D EMARD vordah at gmail.com
Sun May 17 10:25:05 CEST 2020

You can check our ULX3S schematics for low cost GPDI, this
is how we call it, consists from just a connector and capacitors
directly to FPGA :)

for lower resolution be connected directly to the pins. Choose pins
which support serdes, true differential pairs and TMDS electrical spec
if chip has them. If not even general purpose pins will always work for
640x480,  maybe more if you're lucky

It's best to add 8 capacitors 220nF in series with each wire
At moment when cable is plugged, C's will protect the board from
power AC/DC voltage difference or GND temporarily missing

weak +5V/100mA from board to monitor is required,
some monitors will show picture without +5V but some
will also ignore the signal if 5V is missing. It must be really 5V, not 3.3V.

I2C and CEC etc you don't need. Just generate signal with resolution
that all devices support like 640x480 or 1024x768

On 5/17/20, Skulski, Wojciech <skulski at pas.rochester.edu> wrote:
> Magnus:
> another hardware question. Is it safe to connect the Spartan-6 pins directly
> to the HDMI connector? There is some +5V lurking around the HDMI interface.
> The TMDS should be safe because it is terminated to 3.3V at the monitor
> side, but how about the CEC and I2C? In the Pipistrello schematics I can see
> some mysterious unlabeled box to the left of the HDMI (above the audio
> connector). What is that box? A bus switch or some voltage limiter perhaps?
> I am tempted to use my favorite SN74CB3T3306DCU in between the FPGA and the
> SCL/SDA from the HDMI connector. The ultimate protection would be to use a
> TMDS141RHAR redriver which can drive up to 5 meters of the HDMI to the
> monitor. Is it needed, or can the FPGA pack enough ooomph into the cable?
> I do not have actual experience with video HDMI. We used the HDMI gear to
> pump raw data between the FPGAs, but without actually dealing with video.
> Your experience would help!
> Thank you,
> Wojtek
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