[Oberon] HDMI question

[D EMARD]

We are using PCA9306 for i2c, works in both directions.
Signals are DC balanced so if you want to do only output
to monitor, just use C in series to every TMDS wire
value doesn't matter some boards use 100nF  I use 220nF

Spartan6 has all that is needed to make a good picture 1440x900
if your RAM bandwidth allows

We have SDRAM and bandwidth is enough for 1024x768
with 64 colors per pixel. (colors except BW I have never seen, don't
know how to program oberon :)




On 5/17/20, Skulski, Wojciech <skulski at pas.rochester.edu> wrote:
> 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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>>
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