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My doubt is, can I connect a 220pf capacitor to the two terminals of the crystal connected between 18th and 19th pin of an AT89s51. 33pf is to be connected there actually. I am trying to do with 220pf.. but m not getting the required o/p
My doubt is, can I connect a 220pf capacitor to the two terminals of the crystal connected between 18th and 19th pin of an AT89s51. 33pf is to be connected there actually. I am trying to do with 220pf.. but m not getting the required o/p
It should be a crystal across the oscillator pins. 2 nos of 22 or 33pF caps one side grounded and other side one act each of the crystal pins. a schematic attached below.
This isn't recommended but have you tried removing the caps altogether. I was in a similiar situation lately with a AT89C2051 and found that it worked with just a crystal.
But again, don't blame me if your chip dies and if it does work, still get the right values as per the datasheet or your aren't guaranteed anything.
It can work because of stray capacitance I believe.
Wait until you get the right values if you don't want to take risks.
I personally had a few chips laying around so it wasn't much of a risk when I tried it.
The capacitors aren't there to 'ground the noise', they are a crucial part of the oscillator circuit - as suggested, you may be lucky and have sufficient stray capacitance to make it work, but it's not likely to be reliable.
I am afraid I will have to side with Nigel. 220pF is easily enough to completed short out the return side of the oscillator, with the predictable result of the failure to start and if you do not know to look there, complete frustration.
The crystal is in the feedback loop of an amplifier for practical purposes, you short the input to ground and you short the output to the positive rail since it is an inverter (the crystal provides the phase shift needed for the oscillator to run)
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