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Old 19 June 2009, 02:01   #41
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Quote:
Originally Posted by Rabbit80 View Post
I don't have the faintest idea what a TTL signal looks like though
Hi Rabbit80,

A TTL signal is a digital signal where 0V D.C. represents logic 1 and ~2.4V D.C. represents logic 1.
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Old 19 June 2009, 09:05   #42
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erm - I thought it was a timing measurement -ie the time taken between peaks of a sine wave - not a voltage measurement!
Nope. It is an amplitude measurement not a frequency measurement.
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Old 19 June 2009, 12:03   #43
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OK - so how exactly do I generate a pk-pk signal from the TTL signal if that is what my TV requires? What components do I need and how do I wire them into my SCART lead?
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Old 19 June 2009, 12:46   #44
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Looking at that scart - d23 pinout, are we sure the composite video/sync pin is not kicking out analogue syncs?

Would make more sense to me than TTL syncs. And the comp video phono output definately uses analogue syncs so they mustbe generated somewhere...?
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Old 19 June 2009, 14:11   #45
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Bad guess. Did you even read this thread?
Sure, but I thought it had something to do with the pinout. Oh well, got lucky I guess
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Old 19 June 2009, 17:04   #46
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Originally Posted by Silver View Post
Looking at that scart - d23 pinout, are we sure the composite video/sync pin is not kicking out analogue syncs?

Would make more sense to me than TTL syncs. And the comp video phono output definately uses analogue syncs so they mustbe generated somewhere...?
How does this help me
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Old 19 June 2009, 18:13   #47
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OK - so how exactly do I generate a pk-pk signal from the TTL signal
Terminology, pk-pk is not a type of signal it is a type of measurement.

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OK - so how exactly do I generate a 1v signal from the TTL signal
I imagine you use a voltage divider to reduce the voltage from TTL's 2.6v-5v down to the 1v required?

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What components do I need and how do I wire them into my SCART lead?
Don't know.

1 resistor and ohms law? (Or just try 330 Ohm?)

Last edited by alexh; 19 June 2009 at 18:20.
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Old 19 June 2009, 21:09   #48
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I hate my TV

When trying Dreamcast out through TV, I get blank screen when I load a game - on a normal UHF type connection... It is fine in the system menu! If I turn the TV off then back on - I can see the picture (for half a second), but it looks like the interlace is out of sync!
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Old 19 June 2009, 23:07   #49
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How does this help me
Sorry - it does not, I was following on from earlier comments.

However, it looks like my confusion may be down to TTL being used to mean "TTL Level" - i.e. 2/3Volts rather than the original meaning "Transistor-Transistor Logic". Old Video signals were sometimes encoded digitally, often called TTL, with a very limited number of colours etc. I was assuming the sync was digitally encoded....
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Old 19 June 2009, 23:09   #50
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I was assuming the sync was digitally encoded....
It is.
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Old 20 June 2009, 00:26   #51
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It is.
You are of course, correct - all the sync pulses are 0/1 in nature.

So is there anywhere I can see a waveformof the syncs the amiga outputs? Is it identical to - e.g VGA syncs - but of differing voltage levels?
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Old 11 August 2009, 12:36   #52
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Almost got there with my SCART adventure. My A1200 now has a SCART socket in the back (I decided to build one into the Amiga that uses a standard SCART cable ) and works pretty well on some (CRT's and some LCD's) TV's. I have put a 1K variable resistor on the CSYNC line in the hope that I can tweak the voltage. I'll try to post some photos sometime!
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Old 11 August 2009, 18:20   #53
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@ Silver

CH1 (Yellow) is the TTL Csync signal, CH2 (green) is the VSync signal.



I need to test this, put feeding the CSYNC signal via a 1K2 resistor will provide a 300mV sync signal suitable for some video decoder devices. If the 1K2 resistor fails, try a 330 ohm resistor to create a 920mV video signal for the CVBS input.

Ian

Last edited by Stedy; 21 November 2010 at 23:59. Reason: Got my H & V syncs muddled up
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Old 11 August 2009, 18:26   #54
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what is 1k2 ? = 1kohm ?
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Old 11 August 2009, 22:02   #55
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1k2 = 1.2kOhm
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Old 11 August 2009, 22:13   #56
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now I have built a SCART socket into my Amiga, is there anywhere else I can pick up the signal from inside the A1200? A resistor doesn't work for me (tried variable at 0.1 increments from 0.1k to 5k)
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Old 12 August 2009, 00:47   #57
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The A1200 (and A600) both have video encoders, so you could replace the TTL C-Sync with Composite Video. Simply solder a wire from the Yellow Phono Jack to your SCART socket.

Last edited by alexh; 12 August 2009 at 00:54.
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Old 12 August 2009, 01:14   #58
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@Stedy

That's awesome, thanks - wish I had a scope at home...

Ok so standard syncs ~0.5ms Vsync (inc pre-post-equalising periods) at 5V.

Is that csync off one of the d-23 pins or off the composite video connector? I'm assuming the composite video connector has 1v p-p signal and therefore syncs....(i.e. 0.3V syncs)
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Old 12 August 2009, 14:14   #59
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Quote:
Originally Posted by alexh View Post
The A1200 (and A600) both have video encoders, so you could replace the TTL C-Sync with Composite Video. Simply solder a wire from the Yellow Phono Jack to your SCART socket.
I was wondering if that would work. I'll give it a go!

once I have it all up and running, I'll be sure to post a few photos!
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Old 12 August 2009, 23:35   #60
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@Silver

The Composite video output of the A600 is compatible with EIA 343, i.e. 700mV peak white and -300mV sync pulse, when terminated into 75 ohms.

Any video signal, RGB or Composite was measured when terminated into 75 ohms. The TTL signals were measured unterminated.

The CSYNC pulse is a TTL copy of that which comes out on the 1V pk-pk analogue video waveform. I use the TTL CSYNC pule to trigger my scope as the RGB outputs have no sync information.

The RGB outputs are DC coupled, the Composite video output appears to be AC coupled.
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