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Author Topic: Stupid, stupid, stupid, stupid, stupid.  (Read 2387 times)


  • ZX80
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Stupid, stupid, stupid, stupid, stupid.
« on: February 25, 2015, 06:37:58 PM »

I was thinkign a moment about how, why games ran at 50Hz on a PAL monitor because it was impossible for them to refresh faster because that's how fast the mains electricity went and that was that.


I realised there might be a way around it.

Using a split screen method with upper half an almost exact duplicate of the lower half.


It receives Two joystick input raster interrupts, one on the vertical retrace and the other halfway down the screen. So.....


You can have your joystick detect run at 100Hz.


.... Oh, I can't be bothered with this, ther isn't enough time in the whole world.


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Re: Stupid, stupid, stupid, stupid, stupid.
« Reply #1 on: February 26, 2015, 11:57:28 AM »

There may be enough time..... run at 15hz and make use of the extra :)
Coding for the love of it!


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Re: Stupid, stupid, stupid, stupid, stupid.
« Reply #2 on: March 04, 2015, 05:39:25 PM »

Omg you asked for this......

Nah, what I mean is, you can have two raster interrupts, one during VBL and it polls the joystick and scrolls the top half of the screen, then one a bit further down which polls the joystock again and scrolls the bottom half of the screen.

You have enough to do both at 50Hz.

But if you think about it, you're polling the joystick at 100Hz. So you're taking 100 user inputs/sec.

If you then treat the top and bottom half of the playfield as Two screens, running at 50Hz each, because you can't break the 50Hz barrier, you still have Two screens updating at 50Hz, effectively, staggered though, 0.02 secs / 2 = 100 Hz apart.

Ya get mi?

So, instead of each new screen refresh appearing on subsequent screens, there are two screen refreshes per scan.

The top and bottom half of the screen are effectively divided by 0.01 secs of raster time.

You can theoretically do this as many integer times as you like. Three or four screen refreshes per scan.

With only drawback, and I admit it's a pretty big drawback, that your screen doesn't appear in a uniform location in your field of view.

BUT! There's a possible answer.

If you had a device that first showed the top half of the screen and then the lower half, and then the upper and then then the lower, etc, then you effectively have a 100Hz refresh.

Failing a specially adapted device, you could simply Look at the top hald and then the bottom half and back again in 0.01 second intervals.

With a little bit of training you just could pull it off!

See? 100Hz game on a PAL screen.... sort of.
« Last Edit: March 04, 2015, 05:46:46 PM by vapourmile »