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HP 48GX cpu clock speed - cdmackay - 02-26-2020 07:21 PM

I just picked up a second HP 48GX, 2002 manufacture, and was interested to note a different cpu clock speed — as shown by A in the On-D self-tests — compared to my other one (same year).

One is 3.7MHz (roughly), and one is 3.9MHz; by coincidence, both serial numbers indicate week 37 of 2002.

Is that surprising? The wikipedia article suggests that one might expect 3.9 MHz, for GX, especially later models like mine.

Or is it not that simple?

One difference is that the 3.9MHz one has two RAM cards installed, but I doubt that's relevant.

Obviously, I don't expect to notice any difference in practice, and I could consider SpeedUI were I bothered about the 48 speed anyway, so this is just out of interest Smile

thanks!

RE: HP 48GX cpu clock speed - SammysHP - 02-26-2020 07:35 PM

I think this article is a pretty good explanation: https://www.hpcalc.org/hp48/docs/humor/speeed.txt

RE: HP 48GX cpu clock speed - cdmackay - 02-26-2020 07:42 PM

ah yes, indeed Smile

RE: HP 48GX cpu clock speed - cdmackay - 02-26-2020 07:50 PM

There are some interesting comments here, but the answer isn't clear.

RE: HP 48GX cpu clock speed - cyrille de brébisson - 02-27-2020 08:29 AM

Hello,

The 48G chips uses an internal oscillator to generate the internal ~4mhz clock...
This oscillator is not tuned at the factory and, due to large variation in silicon wafers will be different from calculator to calculator. It will also change with temperatures as the physical characteristics of the oscillators component (resistors, NOT gates and capacitor) do vary with these...

Modern CPU uses PLL (Phase Locked Loop), which act as precise multiplicators of a precise cristal to set up clocks, but these are much more complex than a simple 2 NOT gate/1 resistor/1 cap system. Which is what the 48 uses.


[Image: WorlB.png]
Cyrille

RE: HP 48GX cpu clock speed - cdmackay - 02-27-2020 04:56 PM

thanks Cyrille!

RE: HP 48GX cpu clock speed - TomC - 02-27-2020 05:40 PM

Cyrille:

Thank you - good information.

Is this clock available external to the processor? IE could we pipe in an external clock?
Or perhaps another method to control this clock external to the processor?

Regards,,
TomC

(02-27-2020 08:29 AM)cyrille de brébisson Wrote:  Hello,

The 48G chips uses an internal oscillator to generate the internal ~4mhz clock...
This oscillator is not tuned at the factory and, due to large variation in silicon wafers will be different from calculator to calculator. It will also change with temperatures as the physical characteristics of the oscillators component (resistors, NOT gates and capacitor) do vary with these...

Modern CPU uses PLL (Phase Locked Loop), which act as precise multiplicators of a precise cristal to set up clocks, but these are much more complex than a simple 2 NOT gate/1 resistor/1 cap system. Which is what the 48 uses.


[Image: WorlB.png]
Cyrille


RE: HP 48GX cpu clock speed - cyrille de brébisson - 02-28-2020 07:20 AM

Hello,

From memory, the capacitor is external, but I am only about 75% sure of that...
So, you could theoriticaly try to speed up a calc...

Cyrille