Nes 50/60hz workaround?

Nes 50/60hz workaround?
by on (#113679)
Hey everyone.

As you all know or should know by now.
The pal nes can't be modified to output ntsc.
But i recently thought to myself:
what if i overclock the pal cpu to get a similar game-speed as the ntsc nes?
Of course it will still output pal but at least the speed will be the ntsc like speed for all the slowed down games like castlevania.

Would this be possible?

Greets
Re: Nes 50/60hz workaround?
by on (#113680)
It won't work. You could fix the music pitch by overclocking but that's it. The VBlank interrupts will still happen at 50 Hz.

If you overclock both the PPU and the CPU then the VBlank interrupts could happen at 60 Hz, resulting in a normal game speed, but then the video signal would be completely wrong, and very probably unusable.

In other words : It is cheaper/simpler to buy a famicom :)
Re: Nes 50/60hz workaround?
by on (#113681)
Bregalad wrote:
It won't work. You could fix the music pitch by overclocking but that's it. The VBlank interrupts will still happen at 50 Hz.

If you overclock both the PPU and the CPU then the VBlank interrupts could happen at 60 Hz, resulting in a normal game speed, but then the video signal would be completely wrong, and very probably unusable.

In other words : It is cheaper/simpler to buy a famicom :)


I see. Thanks for explanation anyway! :D
Re: Nes 50/60hz workaround?
by on (#113708)
Bregalad wrote:
If you overclock both the PPU and the CPU then the VBlank interrupts could happen at 60 Hz, resulting in a normal game speed, but then the video signal would be completely wrong, and very probably unusable.


Would it though? PAL60 is often an unofficially supported quasi-standard. The only remaining issue I see is the line rate which at 625/60 would generate an 18.7KHz video signal which might be out of range for a TV set.
Re: Nes 50/60hz workaround?
by on (#113710)
The easiest way to get PAL60 would probably be to get an RGB NES and rig up an RGB to PAL encoder.

Here's how it was done in the real world: PAL-M is a variant of PAL60 with a lower color burst frequency that fits better into the "M" band plan used with NTSC. Brazil used it before the 2007 digital switchover. The NES sold in Brazil had an NTSC PPU and a daughterboard that decoded NTSC and encoded PAL-M. Some sets support both PAL-M and PAL60; others don't.
Re: Nes 50/60hz workaround?
by on (#113711)
Overclocking will increase frame rate, but it will make lines shorter and line count will be 312. You need same length lines but only 262 of them for 60Hz video output.
Re: Nes 50/60hz workaround?
by on (#113713)
I am not knownledgable about Video standards, but I am under the impression that PAL 60 is not simply 50 Hz PAL with all timings scaled by 5/6 in order to get 60Hz video, but more like a NTSC timing with PAL colour encoding. I might be wrong though, other people could confirm or deny this.
Re: Nes 50/60hz workaround?
by on (#113714)
Bregalad wrote:
I am not knownledgable about Video standards, but I am under the impression that PAL 60 is not simply 50 Hz PAL with all timings scaled by 5/6 in order to get 60Hz video, but more like a NTSC timing with PAL colour encoding. I might be wrong though, other people could confirm or deny this.

I was thinking the samething.
Re: Nes 50/60hz workaround?
by on (#113715)
Bregalad wrote:
I am not knownledgable about Video standards, but I am under the impression that PAL 60 is not simply 50 Hz PAL with all timings scaled by 5/6 in order to get 60Hz video, but more like a NTSC timing with PAL colour encoding. I might be wrong though, other people could confirm or deny this.

That's how my Swedish friends have explained it to me as well (basically NTSC timing with PAL colour/frequencies). I too hope someone here can shed some light on how PAL60 actually works.
Re: Nes 50/60hz workaround?
by on (#113733)
Bregalad wrote:
I am not knownledgable about Video standards, but I am under the impression that PAL 60 is not simply 50 Hz PAL with all timings scaled by 5/6 in order to get 60Hz video, but more like a NTSC timing with PAL colour encoding. I might be wrong though, other people could confirm or deny this.

Yes. PAL60 is normally defined as 525 lines, 60Hz, using PAL colour encoding. What you'd get from an overclocked PAL NES wouldn't be PAL60, because it'd be 625 lines, 60Hz, using PAL colour encoding. I was using PAL60 as an example to illustrate that deviating from the official standard doesn't always mean things will horribly break. In fact, dual-sync, tri-sync or multisync monitors with a composite input will probably accept the signal without issue. The main question is just how lenient your average consumer CRT TV is. I remember messing around with PowerStrip on a PC with a Radeon card connected to a simple VGA-to-SCART cable, and found that I could increase the scan rate quite a bit above 15KHz before the picture would start rolling on my Philips TV. It could be that 18KHz is too high, but you wouldn't know unless you tried.

It's an interesting experiment for sure, if you don't mind risking a few hardware components in the process. I wouldn't shoot it down just because the video signal output isn't going to conform to a defined video standard.
Re: Nes 50/60hz workaround?
by on (#113783)
Muf wrote:
What you'd get from an overclocked PAL NES wouldn't be PAL60, because it'd be 625 lines, 60Hz, using PAL colour encoding.

Well, it's not really PAL color encoding anymore, because the overclocking would also affect the color carrier frequency output by the PPU (normally ~4.4MHz for PAL, after overclocking about ~5.3MHz), so at best you would get a black and white picture.
Re: Nes 50/60hz workaround?
by on (#113827)
thefox wrote:
Muf wrote:
What you'd get from an overclocked PAL NES wouldn't be PAL60, because it'd be 625 lines, 60Hz, using PAL colour encoding.

Well, it's not really PAL color encoding anymore, because the overclocking would also affect the color carrier frequency output by the PPU (normally ~4.4MHz for PAL, after overclocking about ~5.3MHz), so at best you would get a black and white picture.

Ah hm, good point. I didn't think about that. Yeah, I think that's pretty much the final nail in the coffin for this. :)