Re: Open hardware AV to digital conversion

From: Ingo Korb <>
Date: Sat, 10 Jan 2015 13:12:14 +0100
Message-ID: <> writes:

> S-video is the best what you get from the VIC-II. You don't get a
> better signal from it. No component, no RGB, no SDI, ... This means
> you don't jump over its limits.

But what use is S-Video if you cannot use it because your monitors do
not accept it because it's been phased out?

> Except that I want to make it much cleaner.

I hope you don't mean that you want to reconstruct which of the 16
colors was used for the current pixel and output exactly that - although
this could work for Composite/S-Video output, an improved version with
Component/RGB/DVI/HDMI/Displayport output would look like an emulator
and lose everything that relies on the effects of color decoding.

>> Yes, but... "regular" devices have a slightly different video timing. If
>> I'm not mistaken the C64 outputs half a line less per frame, exactly
>> that half line that is needed to signal an interlaced picture.
> I want the solution to reconstruct the sync pulses itself but what you
> say has to be double-checked. If you say that I may run out of the
> VBLANK time to get the proper timing and remain in sync with the source
> then this would indeed pose a problem, solving which would make the
> whole thing more difficult. I think, however that this is not the case.

The PAL VIC-II outputs 312 lines per frame according to the table shown
at [1], so if you convert those two into fields you end up with 624
lines per field instead of the 625 that PAL specifies. For NTSC the
result would be 526 lines instead of 525.


>> Are you sure that such a signal
>> is acceptable to modern TVs?
> Well - that's the norm. I want to reconstruct the norm signal with
> digital accuracy so that those TVs/upscalers/adapters/etc. don't have
> any excuse for saying "no signal" or displaying garbage.

I'm tempted to implement a large-memory arbitrary waveform generator on
an FPGA board to replay a sampled and modified C64 image to simulate
this, but unfortunately there are some other things I'd like to finish

>> I haven't tried something like that with
>> interlaced signals yet, but when I accidentally generated a 480p signal
>> where two consecutive frames were differing by one or two lines, I
>> mostly saw the familiar "No Signal" message.
> I guess it's understandable in such case as the signal must have seemed
> inconsistent to the receiver.

Yes, but why should your modified signal seem more consistent? My bug
did not concern the number of active lines in the frames, but the total
number of lines, similar to what I suspect the output of your method
would look like.

> As we all know - it's not what will make me or anyone here a good
> retirement ;-)

Aren't we all just doing it to have fun anyway? =)

> So yes, cost is an important factor but what I envision is a
> combination of VIC riser and RF modulator replacement. This gives
> ample space for all processing stages I described.

Good, that also means that you could output standard S-Video signals
from your VIC riser instead of the intermediate levels that the RF
modulator converts to something more standards-compliant.

> In the end I'd be happy to see an unbeatable quality signal on both
> the original DIN and an HDMI socket located more or less in the middle
> of the former RF modulator's length.

A type-D HDMI socket should fit into the opening for the original
modulator output without modifying the case, but I'm not sure if these
things can be soldered without using reflow techniques.

> That was the very first idea I talked about with Gerrit - I wanted to
> reconstruct the sync pulses only but later on I thought that this
> approach, even if it worked, would be only a kind of workaround.

It would result in a much simpler and cheaper solution though, I suspect
you could get away with a single 8-pin microcontroller plus maybe a bit
of analog components if you need to generate a blanking-level output
signal. It would certainly make for a nice addon to those modulator
replacement/vertical stripe remover boards that people have suddenly
started to design everywhere.


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Received on 2015-01-10 13:00:03

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