[Oberon] HDMI question

[Skulski, Wojciech]

D.Emard:

thank you for the useful design information.

> 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.

Spartan-6 has all of this. There is an IP which explicitly used these features on Artix-7. I expect some differences in Spartan-6, but probably not much. Back porting from Artix-7 to Spartan-6 should be possible. Porting to your board is probably more work. 

https://opencores.org/projects/lcd_to_hdmi_output_ip 

> If not even general purpose pins will always work for 640x480,  maybe more if you're lucky

They claim to achieve "1440x900 at less that 60 Hz, maximum 1 gigabit/second/line for Artix7 -1 grade device".

> 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

An interesting suggestion! Are these signals AC-balanced? After reading this I am tempted to insert a redriver. 

> 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.

Very useful, thanks!

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

Magnus pointed out the I2C level translator PCA9306. I will connect these signals if I have pins. I am now redesigning a board with Spartan-6 LX9 in TQ144 to enable Guy soldering the board by hand if he so desires.. ;-) There are only 102 I/O pins in this package.

Wojtek



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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