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'[EE] Digital video'
2011\04\18@200736 by M.L.

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[Resent with tag]

I've been wondering how I might get digital video from an FPGA to an LCD
monitor.

Stepping back, what I'm wondering how to do with no real application is to
draw nice 2-D graphics on a monitor from an FPGA board. I know how to
interface to VGA, but it seems a bit backward to take digital data and
convert it to analog, only to have my digital LCD convert it after going
over a couple feet of cable. Doing some searching, I've found what appear to
be large complicated chips from Analog Devices, but of course their website
is down. Has anyone sent digital data to a monitor, bypassing the computer?
What did you do to accomplish this? How difficult was it?

Basically, what I need is a video "card" that can talk some FPGA dev. board
friendly bus.

Like I said, I have no real application at the moment, I'm just thinking
about how to do it. I just ordered a new FPGA board and (I'll admit) I've
been thinking about the MultiAnalyzer project that died a couple years ago.
With this in mind, I'd be happy with slow update rate. The "large
complicated A.D. chip" has a 36 bit wide bus that operates very fast. I'm
thinking I'd like to stay below 25 MHz bus speed and much fewer than 36
bits.

Perhaps the best way is to just go over USB through a PC application.

-- Martin K

2011\04\18@212956 by Dave Tweed

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M.L. wrote:
> I've been wondering how I might get digital video from an FPGA to an LCD
> monitor.
>
> Stepping back, what I'm wondering how to do with no real application is to
> draw nice 2-D graphics on a monitor from an FPGA board. I know how to
> interface to VGA, but it seems a bit backward to take digital data and
> convert it to analog, only to have my digital LCD convert it after going
> over a couple feet of cable.

Of course, modern LCD monitors do have digital inputs, and from the FPGA's
point of view, driving a DVI/HDMI transmitter chip really isn't all that
different from driving a VGA transmitter chip.

Or you could use something like a Beagleboard as the user interface for your
FPGA project.

-- Dave Twee

2011\04\18@233447 by Herbert Graf

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On Mon, 2011-04-18 at 20:06 -0400, M.L. wrote:
> is down. Has anyone sent digital data to a monitor, bypassing the computer?
> What did you do to accomplish this? How difficult was it?
>
> Basically, what I need is a video "card" that can talk some FPGA dev. board
> friendly bus.

Do you really need the video card, or just something that generates
video signals.

First off, I'd say go with VGA. Tons of dev boards have the necessary
hardware to output VGA. Yes, it's "silly" to go from digital to analog
and back again, but if it suits your purpose why not? Every computer
does the same thing.

If you REALLY want to stick to the digital side, you need a DVI
transmitter. You can use transmitter chips, most will require an NDA to
acquire due to most supporting the DRM that HDMI uses (HDMI and DVI are
physically the same, just slight differences in protocol and
configuration, i.e. DVI supports two links).

As a last stab, you could try doing DVI yourself. Most FPGAs contain the
necessary logic (gigabit transceivers) and pads to physically drive a
DVI sink. The DVI protocol is actually pretty simple, shouldn't be too
hard to put something together (basically it's just a bunch of counters
with some padding).

TTYL

2011\04\19@034846 by Michael Watterson

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On 19/04/2011 01:06, M.L. wrote:
>   but it seems a bit backward to take digital data and
> convert it to analog, only to have my digital LCD convert it after going
> over a couple feet of cable.

So read up on DVI (Digital mode, not Analogue) and HDMI. Basically a clock and a number of data streams.

There are other interfaces to LCD screens, but apart from Displayport not used externally (there are a couple of standard ones used for Laptop screens).

In terms of quality and complexity, using Analogue VGA or Analogue DVI (essentially VGA) is quite good and simple as all you need on the FPGA is a DAC and ironically VGA connection can handle higher resolution than a single DVI port or normal HDMI. It's the LCD VGA in that is more awkward than the FPGA out.

It's really only worth while using digital transmission to the LCD if the distance is 20m or 200m rather than 2m.

2011\04\19@045253 by cdb

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You might be interested in the Freescale and Bluetechnix SBC that Element14 is collecting names for possibly winning one.

http://www.element14.com/community/message/30342#30342

Colin
--
cdb, spam_OUTcolinTakeThisOuTspambtech-online.co.uk on 19/04/2011
Web presence: http://www.btech-online.co.uk   Hosted by:  http://www.justhost.com.au
 

2011\04\19@131809 by M.L.

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On Tue, Apr 19, 2011 at 3:48 AM, Michael Watterson <.....mikeKILLspamspam@spam@radioway.org> wrote:
{Quote hidden}

I did read up on DVI. With a pixel clock of 24 MHz (800 * 600 * 50Hz)
the TMDS interface has three lanes for R/G/B that operate in 10b/8b
encoding - so each lane would be up to 240 MHz for that minimal
resolution. I'm not designing my own board, and I'd be really nervous
about trying to make that work if I was designing my own board.

I can implement a RAM framebuffer in my FPGA and output to a video DAC
such as this:
http://focus.ti.com/lit/ds/symlink/ths8134b.pdf

I think I found what Dave Tweed was referring to when he said that a
DVI chip would be about the same as driving a VGA chip. This chip
takes a 24 bit bus or 12 bit double-edged bus and serializes it to
TMDS for you. If I use this chip I can get back to sending data out of
my FPGA at the pixel rate rather than 10x the pixel rate.
http://focus.ti.com/lit/ds/symlink/tfp410.pdf

Thanks for the info, everyone. It wasn't obvious to me what was available.

--
Martin K.

2011\04\20@090000 by Brendan Gillatt

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On 19/04/11 01:06, M.L. wrote:
> [Resent with tag]
>
> I've been wondering how I might get digital video from an FPGA to an LCD
> monitor.
>
Does it have to be a computer monitor? For fairly cheap you can get an
LCD screen of a fair size with a simple 18bit RGB input (look for the
Sharp manufactured Sony PSP screens on eBay). They are relatively easy
to drive with an FPGA or CPLD, assuming you have enough RAM for a
framebuffer.
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2011\04\20@185453 by M.L.

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On Wed, Apr 20, 2011 at 8:59 AM, Brendan Gillatt
<brendanspamKILLspambrendangillatt.co.uk> wrote:

>
> Does it have to be a computer monitor? For fairly cheap you can get an
> LCD screen of a fair size with a simple 18bit RGB input (look for the
> Sharp manufactured Sony PSP screens on eBay). They are relatively easy
> to drive with an FPGA or CPLD, assuming you have enough RAM for a
> framebuffer.

The tentative plan is to use a 8 bits per pixel in the frame buffer
and a 12 bit palette. The possibility is that I can reconfigure the
bus for 12 bit DDR and get 24 bit color.

I will start out simple though. The FPGA board I bought has an R-2R
DAC attached to a regular VGA port with 3/3/2 bits RGB. Who needs more
than 256 colors, anyway?

-- Martin K

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