Amiga Dual Frequency Oscillator - Help needed!

[Jope]

Well, my 2c:

Most Amiga software worth running runs in PAL 50Hz modes, so perhaps that's why this isn't something that people are falling over each other to get.

It's different with the consoles where 50/60Hz is more relevant.

[BuckoA51]

Many games support 60hz though and run much more smoothly. Fury of the Furries, Lotus Trilogy, Menace immediately spring to mind and there are many more.

[pandy71]

Originally Posted by mark_k

??? How did you work that out? There is less than 1% difference between NTSC and PAL CPU clocks.

I made error - this will be around 60.5Hz ((28636360*60)/28375160)

[Jope]

Originally Posted by BuckoA51

Many games support 60hz though and run much more smoothly. Fury of the Furries, Lotus Trilogy, Menace immediately spring to mind and there are many more.

Yep, and most of us run those in 50Hz. :-)

[BuckoA51]

Why would you run them in 50hz if you had the option of smoother, better gameplay with 60hz?

[Jope]

Me personally, I had an OCS A500 so no 50/60Hz switchability back in the day. In these modern times I've tried the NTSC tooltype with some WHDLoad slaves but most of the games I like to play did not run smoother, they ran faster or glitched otherwise.

But hey, it's not like I'm saying 60Hz is forbidden, I just brought up a point of view that it isn't perhaps as excitement inducing as in the console world.

[BuckoA51]

It's definitely officially supported in a number of games.

Don't you take Amiga gaming as seriously as console gaming?? Shame on you :P

[Jope]

The only gaming I'm serious about is arcade PCBs in my cabinets. ;-)

[JimDrew]

Originally Posted by pandy71

DB23 video port have two input signals related to Amiga clock:
XCLK - this is clock input - 5V TTL level compatible
^XCLKEN - this is strobe to enable external clock input - active logical low '0', 5V TTL level .

With those two signal Any (AFAIK) Amiga can be forced to use external clock, those clock may be different than regular one and as such all dependent timing will be affected (and this how Sybil works - by modifying this clock, Paula may have different transfer speed - side effect will be changes in all system timing - not sure it looks from Amiga perspective (Jim Drew as co-author(?) of Sybil should be able provide more details).

Yes, you can use the XCLK/XCLKEN to feed a new clock for the Amiga. I got this idea one day when playing with a Genlock (which does the same thing). However, I was curious just how far you could tweak the system up and down before it would fail. It turns out that you can go pretty far - far enough to be able to write very short or very long tracks, but the reason I designed SYBIL really was to be able to emulate the speed change of a Mac low density drive. Using SYBIL I was able to read and write in real Mac format using the Amiga. I struck a deal with Readysoft to provide a specific version of SYBIL for them (that they could detect and allow/disallow) to use with their Mac+ emulator, Amax. We produced all of the hardware and were ready to ship and then Readysoft decided that they wanted to make a plug-in card instead and did not follow through with our agreement. I was so pissed that I created EMPLANT to compete directly against them. So, if I would have never been playing with that Genlock that one day, SYBIL would have not been made, and thus there would have never been an EMPLANT board.

[dirkies]

if you have both NTSC & PAL oscillators already, what pin should be connected to a switch and which pins can be soldered to the A500 motherboard?
Have an NTSC A500 here with a fat agnus so I can do PAL too, and would like to have it PAL/NTSC switchable.

[hooverphonique]

Originally Posted by JimDrew

- far enough to be able to write very short or very long tracks, but the reason I designed SYBIL really was to be able to emulate the speed change of a Mac low density drive. Using SYBIL I was able to read and write in real Mac format using the Amiga.

So basically you were changing the read/write bit rate of Paula for the floppy port, given that changing amiga clocks doesn't affect the rotational speed of the drive?

[pandy71]

Originally Posted by hooverphonique

So basically you were changing the read/write bit rate of Paula for the floppy port, given that changing amiga clocks doesn't affect the rotational speed of the drive?

Main clock is changed so All clocks are affected (CPU, Color Clock, CIA clock etc) - this mean video have variable H and V sync also.

[JimDrew]

Correct, SYBIL caused the loss of video when writing long or short tracks (or writing Mac format). The XCLK provides a new base frequency for the entire Amiga, since that all clocks are a multiplier of the color clock frequency, be it NTSC or PAL. The Amiga drives always have a fixed drive speed of either 300RPMs (880K) or 150RPMs (HD).