8.6.4 New Videlity Pixelclock

New pixelclock (Falcon/Videlity)

D.I.Y. "Screenblaster (tm)"
Jo Even Skarstein

• Titan Designs
   

claims that Videlity is a perfect complement for Nemesis. Well, I have both and I have to disagree. Don't get me wrong, Videlity is a superb piece of software, but it's not very well integrated with Nemesis.

The most annoying problem is that Videlity doesn't know when you change the bus-speed. So if you run in a resolution that depends on the system-clock, the screen will be totally messed up whenever you switch bus-speed.

Also, Nemesis wasn't compatible with my ScreenBlaster Inside (Which wasn't very useful to me anyway, because of it's 50MHz clock.) as both use the same control-lines. So when Geir Øyvind Vælidalo came up with the idea to install a permanent "external" pixelclock I just had to try it.

You need...

- An oscillator of the desired speed.
- Preferably a 14-pin DIL-socket.
- Some pieces of wire.
- Soldering tools.

Installation

The installation is quite simple, you have to solder three wires. If you don't bother with the socket, the wires are soldered directly to the oscillator.

Pin 14 of the socket is connected to the positive end of the big smoothing capacitor next to the Videl.

Connect pin 7 of the socket to ground, the negative end of the smoothing capacitor is a perfect place.

Connect pin 8 of the socket to pin 14 on the Videl. There's a solder-pad  5mm from this pin, this is the best place to solder. Scrape the solder-resist coating away from the pad before you solder. Make this wire as short as possible.

Insert the oscillator in the socket (The right way please! Pin 1 is at the square corner.) and secure it with some tape. That's it! You can now make new resolutions with Videlity, just be sure to set "Dot clock" to "Ext". These resolutions will now be entirely independent of bus speed.

I've not used a socket in this installation, simply because I didn't have one available at the time. The blobs covering the pins on the oscillator is hotglue (for insulation and rigidity). The oscillator is fixed to the PCB with double adhesive tape. As you can see I haven't grounded the oscillator according to my own advise (smoothing capasitor), but to the RF-modulator's shielding.

Clock-speed

What clock-speed should you select? That's hard to say, as it depends on your monitor. My lousy SVGA is very picky about frequencies, and pixel-clocks above 40MHz is pretty useless to me. But if you have a very good monitor you might want a 60MHz-clock or above for really high resolutions.

But remember, bandwidth is also an issue here. Too fast clocks will stress the bus and slow down your Falcon considerably. I settled for a 36MHz clock, which gives me a stable picture at 832x624 in 16 and 256 colours without using too much bandwidth.

Legal stuff

This modification works very well with my Falcon, and unless you do something wrong, there's no reason it should do any harm. But just in case: If you decide to to this modification, you do it entirely at your own risk. I take absolutely no responsibility for any damage done to either your Falcon, monitor or yourself!

And remember, always disconnect the Falcon from the mains when you open it! I once touched a live PSU with my nose (don't ask), and it was - to quote Ford Fairlane - "slightly amusing, but mostly painful".

Updated 09/08/98