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G2 screen refresh rate (20200121)
01-24-2020, 06:06 AM
Post: #12
RE: G2 screen refresh rate (20200121)
Hello,

OK, lots to untangle here...

> Cyrille aka "Wolverine" <- my nickname for Cyrille from the last Millenium
My nickname in the last milenium was never Wolverine (which is a name that I did not hear until I moved to english speaking countries, we did not do super heroes in France when I was youg, bar Superman, Zorro and Batman, and our comic books have nothing to do with super heroes)....
My nickname was HPmâd (note the important accent on top of the 'a') since I was 'crazy' (aka 'mad' in my poor english of the time) about HP calculators, and since crazies, in old movies and comics did wear funnels as hats (hence the accent circonflexe on top of the â which is a simplified "depiction" of said funnel (when I was writing it by hand, I would draw the funnel))...

> why flicher and AC frequency are linked.
non-incandessent lights flicker at the AC frequency. it used to be true only of neons in the old time, which meant only office buldings and the like. now that fluoressent and LED (which also flicker) are everywhere it is way more important.
if the screen refresh rate is very close to the light flicker rate, you get a stroboscopic effect (think weels that seems stationnary, or to go slow or backward in movies). this effect reinforce the lighting/visibility of some part of the screen amd make other seem dimmer. since your eye is verry sensitive to contrast, it will enhance this effetct and this will manifest as a type of flicker... since US uses 60hz and the rest of the world uses 50hz, I set the refresh rate at 55hz.

> about outside flicker.
The sun does flicker with 2 main periods super-imposing on each other. so such an effect is, in theory possible, with the sun...
However, since the sun flickering frequency, oen intrinsic, one external are, repectively, 11 years and 24h, we should be good from interference with the prime screen Smile

> frequency range on Prime:
The new frequency selection mechanism allows a setup from 55hz to 120hz.

> drwabacks
To refresh the screen, the CPU must fetch the screen from memory and send it to the screen driver at the rate of 300kb/screen.
so, 60 screen per second is 18MB that needs to be fetched from RAM, 120hz is 36MB.
This has a dirrect impact on RAM bus usage.
When the calculator is 'working' this buss usage will take precedence over CPU needs, so calculations might slow down a little bit (probably barely mesurable except on very memory intensive stuff, partially thanks to cache).
It also has a power consuption impact. 120hz uses (from memory) 40mA more than 60hz. in Idle mode (before the screen dims), this is an extra 10% power consumption! so there is a drback to high refresh rate, which is why you should set it at the minimum frequency that works for you.

Last point, when the screen dims, I lower the frequency by 20 or 30Hz (I do not remember). Since the screen is dimmed, it is much less visible. hence during the time of screen dimming, I can reduce power use.

Here you go, you should have all the info now.
Cyrille

Although I work for the HP calculator group, the views and opinions I post here are my own. I do not speak for HP.
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RE: G2 screen refresh rate (20200121) - cyrille de brébisson - 01-24-2020 06:06 AM



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