# motherboard system timer



## imustbeanidiot (Oct 8, 2001)

Hi all,
Just a small thing really that has been bugging me.
i recently had to send a motherboard back to the supplier due to a fault. My local pc shop tested the mobo & told me that -
"Channel two system timer was faulty".
The supplier of the mobo also tested the board after I returned it & sent me a new mobo without delay so therefore they must have agreed that something was wrong but can anybody tell me EXACTLY what "channel two system timer" means?
Is it part of the bios or a physical part of the mobo?

I only ask because after about 2 weeks of using my replacement mobo the original fault seems to be starting to reappear? ie system just shuts down on its own after about ten minutes. Max cpu temp is only about 42deg & max mobo temp is about 32deg


----------



## imustbeanidiot (Oct 8, 2001)

Please, does anybody know?


----------



## GOTzMADsKILLz (Apr 18, 2002)

The system timer is very important in keeping the features of the motherboard are working correctly.

Interval timer channel 2 failure: might have been the correct one.

You would have to check with your motherboard manufacturer as different manufacturers may use different codes or have different timers set up but for the most part every mobo has it's own clock cycle generators (more than one nowadays since there are more than one BUS on the mobo) to run the BUS's, peripherals etc. It may have been a BIOS problem but it's doubtful as you could have most likely fixed it by flashing the BIOS. 

Seems to me you had a faulty Interval Controller Chip or possibly a Interrupt Controller Chip. There are usually more than one timer on every motherboard controlling everything to ensure that there are no collisions of data along the lines and that data is running and being transferred at the appropriate times. Without them working correctly your computer would not function correctly. It may not provide an answer to your question but for more info you should contact your manufacturer and get info on it to see if you can correct the problem.


----------



## GOTzMADsKILLz (Apr 18, 2002)

Here's some better info I discovered at this location:

http://www.nondot.org/sabre/os/files/MiscHW/TIMER2.txt

It's actual about writing code for controlling the system timer but thought the description of it might help you out.

The system timer interrupt (Int 08) is controlled by an 8253 timer chip. This chip has three outputs, and is also used to drive the memory refresh circuitry and the speaker.

The timer output frequency is obtained by dividing the 8253 master clock frequency of 1,193,180 Hz by a 16 bit divisor. (A zero divisor is treated as 65,536. This is the value programmed by the BIOS, to give a system timer of 18.2065 Hz.) The timer is programmed by sending a control byte to port 43h, followed by a divisor word (low byte, high byte) to port 4Xh where X is the
timer being programmed.

If the sytem timer (counter 0) is modified, an Int 8 handler must be written to call the original Int 8 handler 18.2 times per second, otherwise some system functions (eg time of day) may be upset. When it does call the original Int 8 handler it must NOT send and EOI to the 8259 for the timer interrupt, since the original Int 8 handler will send the EOI also.


----------

