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-   -   Alice Chip Sync Signal Voltage?? (http://eab.abime.net/showthread.php?t=61006)

Ami_GFX 13 September 2011 05:59

Alice Chip Sync Signal Voltage??
Hi All, I'm new to this forum. After reading a lot of old posts today about Amiga Video and the DCE Scanmagic/Flicker Magic, I've joined and have one question.

Does anyone know the voltage levels of the Vertical and Horizontal sync signals on pins 79 and 81 of the Alice chip? Are they TTL or a higher or lower voltage?

If they are TTL, I should be able to do a very simple mod to my DCE Flickermagic to change the sync signal source from the Alice chip to the VGA output of a Sync Strainer which would make the Flickermagic work with my Video Toaster in Genlock mode. If they are a different voltage, I could still do it but it would take a few more parts and bit more work.

Thanks in advance

alexh 13 September 2011 10:41

The Scan/FlickerMagic is designed to take TTL level inputs.

I know this because it was designed to use an alternate connector which takes sync from the 23-pin D RGB connector on the back of an Amiga instead of the clip over the Alice.

Ami_GFX 13 September 2011 15:35

Perfect, that means it will take the signals from a Sync Strainer which is attached to the RGB port. And the internal and external Vga cables I'll need to do this will cost me around $12. And maybe a small DPDT switch so I can switch sync sources if I want. There's already a hole for another DB15 connector on the vga bracket that came with the Flickermagic. Thanks alexh


Ami_GFX 24 September 2011 02:58

Ok, I tried it today and it works but not very well. The toaster screen is a bit distorted and has horizontal lines running across it. The sync from the regular amiga modes works fine, no noticible difference than from the Alice chip but not so in genlock mode. It looks like the horizontal sync the Sync Stainer derives from the composite sync is not occuring in the right relationship with the video information.

alexh 24 September 2011 10:28

You'd have to explain to me the nature of the sync strainer and the chain of video devices (RGB + Sync) for me to understand what is going wrong.

I imagine that one of the devices delays the video pixel data but not the sync (or vice versa)?

From what I understood a genlock syncs the Amiga video to an external source?

Ami_GFX 25 September 2011 02:32

The sync strainer is is a dongle that attaches to the Amiga RGB port and is intended to be used with the Video Toaster. When the Toaster is started, the Amiga goes into genlock mode and the Horizontal and Vertical sync signals are set to 7.8khz and only composite sync is outputed from the RGB port. The 1080 monitors have a composite sync input and function with the Toaster but most other monitors, even old 15khz CGA ones don't, and the Sync Strainer separates the 15khz horizontal and vertical sync signals from the composite sync and outputs them.

In genlock mode, the Amiga can be synced to an external video source and Amiga graphics can be overlayed onto incoming video. The Video Toaster is the the best genlock device ever made for the amiga but even a Commodore 2300 will do the basic genlock functions. This limits the Amiga video to frequencies that are compatible with NTSC or PAL video signals. The basic 15khz Amiga modes work but no DBLNTSC or DBLPAL and some 15khz display modes work better with a genlock than others.

I've changed the sync input on the Flicker Magic from the horizontal and vertical signals on the Alice chip to the output of the sync strainer though a 15 pin VGA input port I added to the Flicker Magics bracket.

At this point, my next step is to dig out my oscilliscope and take a look at the sync signals to see what the differences are. The distorted video is very stable which is a good sign and indicates a timing issue with the horizontal sync signal and the rest of the video signal.

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