FPGA Central

On some other thread, MikeJ wrote:
>
> I usually try and keep work and the games separate, but it
> would make an excellent platform and save me finishing the
> DDR controller !!
> I have a broadcast serial digital 720P output module somewhere,
> but what I need to make is a DVI output I think ....
>
If you ever spot ( or need help writing/testing )
a FPGA DVI transmitter, let us know!

I've been thinking about trying that for a small S3E
home project; lots of colo{u}rful pixels with only a
few differential output pins and no PHY.

Seems like a simple bias network could shift the
(DC-balanced) encoding scheme from LVDS to TMDS
levels ( or just use an S3A with TMDS drivers )

Max resolution would be limited by the FPGA I/O rates
to say a 60-80 Mhz pixel clock; I think that gets you
into (or near) 1024x768 territory.

IIRC, you can map the DVI-D signals directly onto an
even smaller HDMI connector for a really tiny board
( PS/2, HDMI, VQ100 FPGA )

have fun,
Brian

I looked into this, then realised you can buy a small chip which not only
had a decent DAC to give you RGB analogue outputs, it also drives DVI.
There is one on the cheaper V5 eval board from Xilinx. As I need a DAC
anyhow it seems the way forward ...
/Mike

"Brian Davis" <[email protected]> wrote in message
news:[email protected] oups.com...
> On some other thread, MikeJ wrote:
>>
>> I usually try and keep work and the games separate, but it
>> would make an excellent platform and save me finishing the
>> DDR controller !!
>> I have a broadcast serial digital 720P output module somewhere,
>> but what I need to make is a DVI output I think ....
>>
> If you ever spot ( or need help writing/testing )
> a FPGA DVI transmitter, let us know!
>
> I've been thinking about trying that for a small S3E
> home project; lots of colo{u}rful pixels with only a
> few differential output pins and no PHY.
>
> Seems like a simple bias network could shift the
> (DC-balanced) encoding scheme from LVDS to TMDS
> levels ( or just use an S3A with TMDS drivers )
>
> Max resolution would be limited by the FPGA I/O rates
> to say a 60-80 Mhz pixel clock; I think that gets you
> into (or near) 1024x768 territory.
>
> IIRC, you can map the DVI-D signals directly onto an
> even smaller HDMI connector for a really tiny board
> ( PS/2, HDMI, VQ100 FPGA )
>
> have fun,
> Brian
>

Brian Davis <[email protected]> writes:
> Seems like a simple bias network could shift the
> (DC-balanced) encoding scheme from LVDS to TMDS
> levels ( or just use an S3A with TMDS drivers )

Can you get TMDS drivers that aren't part of a DVI transmitter chip
(which also does the encoding)?

It doesn't appear that DVI transmitter chips cost much, so is it
really worthwhile to try to avoid using one?

Eric Smith wrote:
>
> Can you get TMDS drivers that aren't part of a DVI
> transmitter chip (which also does the encoding)?
>
The only thing I've spotted are the HDMI mux chips,
which do TMDS -> TMDS ( e.g. AD8190 )

>
> It doesn't appear that DVI transmitter chips cost much,
> so is it really worthwhile to try to avoid using one?
>
and MikeJ wrote:
>
> I looked into this, then realised you can buy a small chip
> which not only had a decent DAC to give you RGB analogue
> outputs, it also drives DVI.
>
I think that makes great sense for a larger board,
especially if you also want the analog outputs.

However, once someone writes a DVI Tx encoder and works
out a driver scheme for the S3E (or uses TMDS on S3A),
DVI is only a connector away...

Beyond than the really important home projects,
like hi-def Asteroids, I also have some homebrew
RF test equipment in mind.

In that case, if I'm doing several functions in one
small FPGA, I'd much rather have only 4 LVDS pairs
switching at my reference frequency, as contrasted
to 12-24 CMOS lines, driving another chip, switching
at its' own variable reference clock.

I hopefully will have an S3E board set up for other
purposes in the next month or few, I'll try to look
at some LVDS -> TMDS biasing schemes when I do.

Brian

> Beyond than the really important home projects,
> like hi-def Asteroids, I also have some homebrew
> RF test equipment in mind.
>
>
> I hopefully will have an S3E board set up for other
> purposes in the next month or few, I'll try to look
> at some LVDS -> TMDS biasing schemes when I do.
>
Yeah, it can't be that hard. If you figure out the analogue stuff the DCI
encoding is fairly easy I think.
Wonder if you can get away with patching a socket onto the S3E board, I have
one on my desk

no, don't distract me, I'm in the process of releasing Frogger and
Scramble - had enough of real work for this morning !!

/Mike

On Jun 11, 3:30 pm, Eric Smith <[email protected]> wrote:
> Brian Davis <[email protected]> writes:
> > Seems like a simple bias network could shift the
> > (DC-balanced) encoding scheme from LVDS to TMDS
> > levels

Yes, but it would not be HDMI or DVI compliant. We do this from the
LVDS outputs on a Virtex4 to a MAX3814 cable equalizer. Simple
capacitive coupling works, because there is a current source (pull up)
in the CML inputs on this chip.

> Can you get TMDS drivers that aren't part of a DVI transmitter chip
> (which also does the encoding)?

As above. Be careful, there are a number of things that won't work.
Most CML stuff we looked at has a pullup in the ouput driver (which is
not compliant with HDMI), instead of the input, which would also
require pullup resistors to bias. Many of the TMDS muxes, are simple
analog muxes, and not CML drivers. Cable equalizers are the only
things that we found a year ago that seemed reasonable choices.
Market may have changed.

> It doesn't appear that DVI transmitter chips cost much, so is it
> really worthwhile to try to avoid using one?

8 IO pins total required on the FPGA. Ability to embed audio or other
data for HDMI. Complete control over the protocol.

To go from an 8 bit data stream to a differential pair with TMDS
encoding running at the max toggle rate of the FPGA pins is not a
terribly difficult design to do. Three of these in parallel (with a
very slight difference, depending on which channel it is) makes a
complete interface.



Regards,
Erik.

---
Erik Widding
President
Birger Engineering, Inc.

(mail) 38 Chauncy St #1101; Boston, MA 02111
(voice) 617.695.9233
(fax) 617.695.9234
(web) http://www.birger.com

On Jun 11, 2:42 pm, "MikeJ" <[email protected]> wrote:
> I looked into this, then realised you can buy a small chip which not only
> had a decent DAC to give you RGB analogue outputs, it also drives DVI.
> There is one on the cheaper V5 eval board from Xilinx. As I need a DAC
> anyhow it seems the way forward ...
> /Mike

> > Brian- Hide quoted text -
>
> - Show quoted text -

Whats the device that has DAC and DVI outputs? does it also have a
color space converter? Ycrcb to RGB??
The only one I saw was a chrontel 7303 and they never answer my calls
or emails...
thanks
-Bill

ch7301c
http://www.chrontel.com/products/7301.htm

I am rather worried about sourcing it though.


"ZR1TECH" <[email protected]> wrote in message
news:[email protected] oups.com...
> On Jun 11, 2:42 pm, "MikeJ" <[email protected]> wrote:
>> I looked into this, then realised you can buy a small chip which not only
>> had a decent DAC to give you RGB analogue outputs, it also drives DVI.
>> There is one on the cheaper V5 eval board from Xilinx. As I need a DAC
>> anyhow it seems the way forward ...
>> /Mike
>
>> > Brian- Hide quoted text -
>>
>> - Show quoted text -
>
> Whats the device that has DAC and DVI outputs? does it also have a
> color space converter? Ycrcb to RGB??
> The only one I saw was a chrontel 7303 and they never answer my calls
> or emails...
> thanks
> -Bill
>
>