Why does an NES run slower at a lower frequency?

Thread Starter

jlawley97

Joined Oct 5, 2019
18
I understand that lower frequency means less peak to peak per second.
But if the voltage is being rectified and a significantly large capacitor is used to get rid of the ripple so that there is a solid line. Then why would the frequency matter if the power is DC before it interacts with 99% of the components? especially if Vrms is not effected by frequency?

talk to me like Im stupid here, I really want to understand
 

ericgibbs

Joined Jan 29, 2010
13,652
hi j97,
You can rectify and smooth, by using a large smoothing capacitor, to create a suitable working voltage for most components, from almost any voltage frequency.

E
 

Yaakov

Joined Jan 27, 2019
3,517
I understand that lower frequency means less peak to peak per second.
But if the voltage is being rectified and a significantly large capacitor is used to get rid of the ripple so that there is a solid line. Then why would the frequency matter if the power is DC before it interacts with 99% of the components? especially if Vrms is not effected by frequency?

talk to me like Im stupid here, I really want to understand
NES as in Nintendo?
 

Ramussons

Joined May 3, 2013
1,062
As ericgibbs posts, frequency is not an issue as far as there are no transformers. If there are, oh boy! the frequency will make one hell of a difference.
 

scorbin1

Joined Dec 24, 2019
90
From my understanding the differing speeds has less to do with the Line input voltage and more to do with the refresh rate of PAL(25) interface vs NTSC(29.97) interface. It seems that game developers created content depending heavily on this refresh rate to set timing, so playing the same title on a PAL version would definitely affect the speed of the game. I wouldnt think it would have a great affect, but then again we are talking about nearly 17% difference in speed, that could definitely have a significant impact.
 

MrSoftware

Joined Oct 29, 2013
2,015
Assuming we're talking about a game console, then @scorbin1 could have the answer. Forget the power supply frequency for a moment, what is the refresh rate of the screens you're using in both cases? It cannot redraw the screen faster than the refresh rate.

Side note: Does any modern screen even have NTSC and PAL settings anymore? I'm guessing most are various flavors of the HD standards.
 

scorbin1

Joined Dec 24, 2019
90
I would think the RF/Ant input, when tuning to analog channels, would still have to comply with either NTSC or PAL depending on your region. I think old gaming consoles like the NES are probably the only ones still using it though, as at least in the USA the FCC forced all broadcast stations to digital in recent years.
 

Thread Starter

jlawley97

Joined Oct 5, 2019
18
From my understanding the differing speeds has less to do with the Line input voltage and more to do with the refresh rate of PAL(25) interface vs NTSC(29.97) interface. It seems that game developers created content depending heavily on this refresh rate to set timing, so playing the same title on a PAL version would definitely affect the speed of the game. I wouldnt think it would have a great affect, but then again we are talking about nearly 17% difference in speed, that could definitely have a significant impact.
ahhhhh okay so it is not the nintendo entertainment system its self but rather the televisions they are played on
that makes more sense to me
 

scorbin1

Joined Dec 24, 2019
90
ahhhhh okay so it is not the nintendo entertainment system its self but rather the televisions they are played on
that makes more sense to me
Yes and no... Really it's the software(the game) that's the culprit. When programming games, timing is obviously very important, especially on older single threaded systems like the Atari and NES. Modern games will spawn several threads (probably being VERY generous there), for example one thread to update the output (the screen), one thread to calculate weather or not two objects interacted and decide if a variable needs to change, one thread accepting user input, etc... As I said on these older systems they were not capable of multi-threading or even able to attempt a poor emulation of multi-threading. So the programmers had no choice but to find creative ways to implement their games. They would write a routine that would loop continuously, first it gets input from the user, then it calculates what changes the users input should cause, then it updates the screen, then it loops back around and gets input from the user again. So while it's updating the screen, it can't accept input from the user and it can't process what changes should be effected. So the game only receives input in the interval where the CPU is not updating the screen or calculating changes, which happens between each frame. In a PAL system this is at a frequency of 25fps(Hz), with an NTSC system that frequency jumps up to 29.97fps(Hz). So while the processor may run at a higher frequency the game is effectively running at the frequency of the refresh rate.

Another likely big factor, that I actually ran into while doing some research for this reply, is that the CPU in the NTSC version of the NES and the PAL version of the NES actually run at different frequencies. Likely this was due to the fact that they ran at a multiple of their respective refresh rates to simplify programming the refreshing of the screen. I think this could actually have a multiplying effect when considered with my previous paragraph.
 
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