9 Jul 2012

LoW FuSe bits


     As i explained what are the uses of fuses and how they are to be used now we will only discuss what LOW FUSE BITS are used for .

         FUSES            DEFAULT settings
     1. BODLEVEL   ----    1
     2. BODEN         ----    1
     3. SUT1             ----    1
     4. SUT0             ----    0
     5. CKSEL3        ----    0
     6. CKSEL2        ----    0
     7. CKSEL1        ----    0
     8. CKSEL0        ----    1

BODLEVEL  --   This fuse bit we set when we need the brown out detector. Like you have a application which should Reset when the input voltage is less than 4.5 V and another as when ever the voltage goes below 2.7 V it should get reset .

So, the first requirement can be achieved without enabling this fuse you get the trigger level of 4.5V and for second requirement you need to enable or program the fuse to '0' so that trigger level changes to 2.7V (this is used when you need you circuit to work even you have voltage less than 5 . In some conditions it require .

BODEN        - - This fuse bit we set for enabling the Brown Out Detector .

SUT1  ,  SUT0   :
                       This by default setted to the maximum startup time. In order to change the startup time we use them. There are different levels of startups you should refer datasheet in clock source section . Based on your application you should program these bits


                       These fuses are used for selecting the frequency of the clock at which it should run . For different frequencies these fuses changes same as i said garing the microcontroller before it starts working. These fuse bits are like gares if you don't gare them properly you may loose your microcontroller or it may not work as you like it to work.

Finally what i mean to tell Read these bits clearly in data before you program it because you may messed up with the fuse setting some time so before setting fuse bits make  yourself  comfortable before you decided to write them on MC . ok

At beginning it looks like it is difficult once when you are some practice you automatically program for what ever you require ok.

Learn them well .........................................

How to work with them in avrdude :   click here

After this will go  to Lock bits which are also important to be discussed  in next tutorial . Link to Lock bits

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