Effects of Over Clocking??

Almost *every* device manufacturer does that. And almost every device can be overclocked to some extent. If you look at the specification for a device, you might see it is rated for 25 MHz max over the voltage range 3.0 - 3.6V and temperature range -20 to +85 C. That means the manufacturer has characterised and spot-tested the devices over this entire range. If you run it at room temperature and 3.3V, you will be able to overclock substantially. You'll get even more at optimal conditions (probably close to 3.6V and -20 C) - the fastest speciality PC's have a miniature freezer inside.

You can also consider how manufacturers test and characterise their parts. Devices are made in batches, and random parts from these batches are spot-tested at clock, voltage and temperature extremes (for some types of device, all devices are tested). They are then divided up and marked according to what sales and marketing require. So if a part runs fine at low voltage, high temperature and high speed, it could end up marked as any of these parts depending on the requirements. Thus when you buy a 25 MHz, 105 C part it might run fine at 50 MHz, 20 C.

When testing your own systems, it is not uncommon to overclock to stress the card a little more and check for tighter timing margins.

Of course, if you are making products to sell, you normally want to stick to the limits the manufacturer gives you.

Reply to
David Brown
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Just for knowledge sake of it... i want to know if it is anyways possible for a processor to detect the feed frequency, without using any internal clock as reference.. i.e a processor knows that it is fed with a clock of X Mhz.

Reply to
adonis

Only if there is some known reference signal, such as a 32768 Hz watch crystal or 50Hz mains etc. signal would be available.

However, I agree completely with Grant that it would be stupid if the processor would reprogram the PLL.

While it might make some sense to limit any overclocking, it would be very stupid, if I wanted to underclock a system either to save power or enable some x86 processor to run at 70+ C ambient temperatures and the PLL logic would force the nominal clock speed.

Paul

Reply to
Paul Keinanen

In general, the answer is no. The only way a processor could know what frequency its clock has is if it has an independent timing source with a known frequency.

Reply to
David Brown

Is it possible to underclock a processor?

Reply to
Daniel

Some processors have a (non-zero) minimum clock frequency, either because they are not static or because they use something like a PLL with a limited guaranteed operating frequency range to generate the clock, so yes, you could violate that datasheet specification.

Best regards, Spehro Pefhany

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Reply to
Spehro Pefhany

Pretty often there is a minimum clock frequency requirement for the peripherals like flash/eeprom or ADC.

Vladimir Vassilevsky

DSP and Mixed Signal Design Consultant

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Reply to
Vladimir Vassilevsky

Sure. Some processors have a minimum allowed clock, some you can clock all the way down to DC. Many of the processors aimed at the embedded market can be clocked as slow as you like. I know a lot of people running "16MHz" processors at a few tens or hundreds of KHz. 32KHz is pretty common for low power applications.

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Reply to
Grant Edwards

Yes, as long as you don't go below the minimum requirements. Some processors are fully static (i.e., you can stop the clock entirely), while others require a minimum speed. Microcontrollers with PLLs will often have minimum requirements, but you can set the PLL for low speeds in software. Another thing to watch for are dynamic ram, which has minimum speed requirements.

Underclocking is often done to save power. It can also be useful if you are running in extreme environments, such as high temperatures - processors will typically run well above their specified temperature range if they are underclocked.

Reply to
David Brown

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