Robolab Technologies Pvt Ltd | WHY YOU NEED A CLOCK SOURCE
The clock for the AVR is its heartbeat. It basically defines when a processor will do an instruction. Normal instructions for the chip take between one to three clock cycles to complete; a clock cycle is the low-hi-low transition of the clock. So the faster the clock runs, the faster the chip works. This is why a Pentium 1 GHz chip is a LOT faster than a Pentium 100 MHz chip - many more instructions are executed per second. However be careful - the speed of the clock doesn't actually mean a lot. One processor could take 1 clock cycle to move data from one register to another, but another processor could take 2 clock cycles to do the same thing. This means that processor number 2 will have to run at double the speed as processor 1 to do the same instruction in the same amount of time! The key here is a little rating called MIPS (Million of Instructions Per Second), which is surprisingly (not) how many instructions the chip could do in a second at a specified clock frequency. Anyway the point is that you need something that tells the processor when it will be doing instructions (the clock). Even THEN that’s not a perfect indicator of speed, as stuff like on-board cache, bus width and loads of other things make a huge difference! Selecting a Clock Source There are a few different ways to generate a clock for the AVR. You can use an external clock that feeds in the low-hi pulse stream, a crystal or a ceramic resonator. A few of the chips even have a built-in RC oscillator! We'll talk about properly interfacing them in a second, first lets see the advantages, disadvantages of each. External Clock This one is fairly easy - all you do is have some circuit that creates TTL compatible logic pulses, and feed those into pulses into pin XTAL1. Your external clock could be a cesium-based atomic clock, or a chipmunk spinning a wheel, with a unit counting the RPM of the wheel. The external clock should be very clean and fall and rise times should be fast.
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1 Comment

  • fiverr seo

    Really informative article post.Really looking forward to read more. Awesome.


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