# IC 8253/8254 mainboard timer



## RFB (Nov 18, 2009)

Hello,

This is my first post and I'm not sure that I have chose the right forum, but this is a clock related matter. I have an application that I'm writing and I need an accurate high frequency timer capable of 100kHz.

Now before you say that is impossible I would like to inform you that it is currently being done in Windows XP on my PC without any additional hardware and it consumes only 6 to 7 percent of the processor time, but not with my software.

I have been researching this matter for a couple of years, but not with determination I have had lately. I ran across this article: 
http://www.dedicated-systems.com/magazine/01q3/2001q3_p077.pdf and I thought that I had found something so I started studying the 8253 Programmable Interval Timer, or PIT as it is more commonly called. It is stated many times on the internet that most all modern computers have an 8253/8254 PIT.

After spending a couple of hours studying the chip I decided to pull out one my spare mainboards so that I could get a visual on the chip. That is when all of my effort became a waste of time as my mainboard does not have anything that I can identify as a timer. South bridge is SiS645DX and North bridge is SiS962.

Can any of you shed any light on this subject?

RFB


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## Aus_Karlos (Mar 10, 2007)

Many motherboards today support HPET mode which is enabled via the BIOS (CPU must support the function and i think its only avalible on Intel M/B)
http://en.wikipedia.org/wiki/High_Precision_Event_Timer

I hope this helps...


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## RFB (Nov 18, 2009)

Aus_Karlos,

Thanks for your input. I can just almost recite all of the web pages that deal with this matter. The attached combination picture shows the application that has a 100kHz timer and the Win XP Task Manager. I had never actually ran the frequency at maximum output so I was unaware of the CPU time consumption, but 12% is an acceptable rate. The pulse rate is not just a number in TextBox because it is a signal emitted from a parallel port pin and it can be verified with a scope. That is the driving force behind my determination.

RFB


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