DIY Screenblaster mod

[SoundDoctor]

Hello folks,

Having taken delivery of my shiny old stock 14mb / 160mb Falcon 030 I have been digging around itching to do all those mods I read about that were not around when I gave up my old Falcon back in 1996 or were published while I didn't have one.

My machine is pretty stable and doesn't seem to have any of the standard mods in place - except a little jumper on one pin of the videl chip that goes to a via near the leg of the chip - probably a repair on a pulled trace. The only real problem I can find with it is the up cursor key a bit flakey, and the RTC is dead. I have a Dallas 12887A on order but will try the 'adding a battery' mod first...if I screw that up I'll replace with the new chip. I might make a little adapter using using two DIP sockets and a bit of this Vero board trimmed down to relocate the RTC to a more roomy location:
http://www.ebay.co.uk/itm/Copper-Protot ... 2a1897fe5b

I'm not that interested in pushing the Falcon to high bus or CPU speeds...yet. One thing I'd like to do though is increase the VGA resolution. I've got Videlity and it's by far the easiest to use of the software only screen enhancers that I have tried. I found this DIY internal Screenblaster mod online here:

http://atari.nvg.org/pixelclock/pixelclock.html

It looks like an easy and simple mod to add a bus independent external clock to the videl chip that Videlity can see.

Has anyone got any thoughts on this simple mod? Has anyone tried this with newer TFT VGA screens that might not play to well with wacky frequencies? My real stumbling block is knowing which oscillator to use. If I install a DIP socket I can try a variety of clocks above 32MHz but how far to go without stressing the bus, slowing the falcon to a crawl, and ending up with a blank screen or 'signal out of range' message for my trouble?

Thoughts most welcome

Sounddoctor

[joska]

I found that a 36MHz pixelclock was a good compromise between resolution and bus load. With modern LCD monitors you can use a pretty low refresh-rate (and even interlace) and still get a good picture.

[SoundDoctor]

I found that a 36MHz pixelclock was a good compromise between resolution and bus load. With modern LCD monitors you can use a pretty low refresh-rate (and even interlace) and still get a good picture.

It's your guide I was looking at joska! I would have asked you but your excellent site is dated 2002 and I wasn't sure how to contact you. Being new to the forum I didn't know you were here! Thanks for the confirmation. I was thinking about 40MHz but wasn't sure of the benefit of the higher clock.
I was thinking I could use the same crystal oscillator to feed both the external pixel clock for the Videl and as a clock for the FPU accelerator by gøv (also found on your page). It's probably not a good idea - my thinking is the clock signal wire should be as short as possible so I would be better to use two separate crystals for both mods to be stable. I suppose the need to do these mods is because Atari originally cut corners and shared the same clock source for too many components that compromised the system and restricted some devices in the first place.

Cheers

[joska]

I was thinking I could use the same crystal oscillator to feed both the external pixel clock for the Videl and as a clock for the FPU accelerator by gøv (also found on your page). It's probably not a good idea - my thinking is the clock signal wire should be as short as possible so I would be better to use two separate crystals for both mods to be stable.

You should use separate clocks. The FPU (and DSP) can be clocked at 50MHz, but anything above ~40MHz is not really usable for a pixelclock on an otherwise standard Falcon.