Hi,
Not having much luck with Google for lack of better keywords but the question came up today about what computers (desktops) use as a clock.
Is it really an RC circuit or does it require something more precise like a crystal oscillator?
I was thinking that an RC type circuit wouldn't be accurate enough but the argument was put forward that that is the cause for a computer slowing down due to over heating.
Can anyone confirm/deny this?
Thanks In Advance,
Michael
MC146818. Actually a MC146818 functionality is embedded into chipsets in our days.
Standard 32.768kHz crystal
Wow. What an interesting idea.
Vladimir Vassilevsky DSP and Mixed Signal Design Consultant
google cmos clock
There are MANY clocks inside a modern PC, for various communication chips, for the video, for the real-time clock (RTC) and for the CPU. Most or all are crystal oscillators.
Sounds like some kind of protection behavior. Also, CMOS chips generally cannot be clocked as fast at high temperatures without errors occuring, so a CPU which is overheating may experience soft errors (eg. the system might lock up) especially if it is being operated outside of specifications (eg. "overclocked").
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
Windup type!. Build in obsolescence
-- "I\'m never wrong, once i thought i was, but was mistaken" Real Programmers Do things like this. http://webpages.charter.net/jamie_5
Not to brag or anything, but those guys use our V860 pulse buffer modules to distribute the 1 pps ticks from a lot of atomic clocks.
John
Computors use crystal oscillators, mainly for three reasons:
1) They're dirt cheap 2) They allow precision timing of for real-time applications such as: . Digital signal processing . Control of external devices 3) Most Microcontrollers have the support circuitry for xtal oscillators built in.
Are there *any* microcontrollers in a modern PC (not talking about the keyboard or other peripherals)?
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
I think the question referred to PCs rather than controllers.
So a relatively slow crystal is used for the CMOS ? What about the CPU itself ? Does it use the same clock reference multiplying it with a PLL ?
R
No. Look at your motherboard and you'll see several crystals. The real- time clock uses one crystal, the CPU uses a different one, the serial port uses a different one, USB uses a different one etc.
Alot of them do have a PLL multiplier,or something similar. It used to be set with jumpers,along with the main "bus speed",CPU voltages,etc,etc... Nowdays I think it's usually in the BIOS/CMOS.. In the system settings there is often a Bus/Clock speed,and Multiplier/Ratio for the system speeds. (-that's how you overclock them,turn up the speed/ratio.)
Spehro Pefhany wrote in news: snipped-for-privacy@4ax.com:
Optical drives, HDDs, and USB devices generally have some sort of microcontroller on them. I believe power is managed by an always-on microcontroller of some sort. Hardware modems have a controler. Some add-on cards may have a microcontroller (my TV card is made with a version that has a microcontroller to decode IR remote signals).
There is at least one microcontroller on the motherboard besides the main CPU: the 8042 keyboard interface (often embedded into the chipset). There could be any number of microcontrollers on the cards and devices.
Vladimir Vassilevsky DSP and Mixed Signal Design Consultant
Vladimir Vassilevsky wrote in news:OSdEi.14180 $ snipped-for-privacy@newssvr25.news.prodigy.net:
I though they done away with that and just did it in software, with some GPIO or a state machine.
On Fri, 07 Sep 2007 14:55:15 GMT, in sci.electronics.design, Gary Tait bloviated:
"(not talking about the keyboard or other peripherals)?"
-- Does the name Pavlov ring a bell? Aratzio - Usenet ruiner #2
On Fri, 07 Sep 2007 15:11:42 GMT, in sci.electronics.design, Vladimir Vassilevsky bloviated:
"(not talking about the keyboard or other peripherals)?"
I believe that the question of whether to count internal devices such as optical drives and HDDs was peripherals ws asked but never answered. Given that, it would be reasonable to infer from the word "in" and the fact that the example (keyboard) isn't in the PC, that internal components are to be counted.
Are the north and south bridges counted as peripherals?
For a while I worked on ruggedized portable PCs for the military. In addition to the 80486 or Pentium main processor, there was a battery- management micro, a display backlight and heater control micro, a keyboard/trackball micro, and others depending on the optional plug-in boards requested.
Motherboard components only. So far the count is zero (a keyboard controller integrated into an LSI is not a microcontroller).
Not from a system point of view.
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.