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Problem with clock amplitude in PIC18F4320

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tom_hanks

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any quik suggestion....

I am using a PIC with 30 mhz.
on pin PIC is generating 7.5Mhz ...
this clock I need to feed to PIC itself and other Pheripheral chip...

i can see the 5v for PIC output, but when I am connecting directly this pin to PIC input and pheripheral..
then voltage is dropping down to 600mv.

i used ac termination but still no good..

tom,
 

A.Anand Srinivasan

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Re: clock amplitude ??

try using a buffer with very good current sourcing/sinking capabilities.....
 

tom_hanks

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Re: clock amplitude ??

that is the problem sir...
i can only use discrete components...

so i used ac termination R1=330;R2=220

i can only use R,C...due to budget & space problem..


any other way
 

A.Anand Srinivasan

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Re: clock amplitude ??

if possible try using an single supply opamp in comparator configuration... if this is also not possible... tell me what all components you can use.....
 

tom_hanks

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Re: clock amplitude ??

im using PIC18F4320, on
Pinout

pIN_A7:OSC1/Input = 30Mhz oscillator (EC mode)
PIN_A6:uP_CLK/output =7.5Mhz(Fosc/4)

PIN_C0:INT_CLK/input = 7.5MHz (Pin_A6 is connected to PIN_C0)

ADC chip pin out
CLK:input = 7.5Mhz (Pin_A6 is connected to CLK)

I do not have schematic, this is prototype board.
 

blueroomelectronics

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clock amplitude ??

The 18F4320 has a maximum external oscillator speed of 25MHz, it's clearly stated on page 3. Internally it's PLL can do a 4x multiply on a 10MHz crystal to run it at 40MHz but the PLL will generally fail at much above 10MHz. You prototype board will also have way too much stray capacitance for MHz operation.

Advice, use a 7.5MHz crystal instead.
 

tom_hanks

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Re: clock amplitude ??

Hello Blueroom,

Thanks for reply...
in DS(PG.3), it is mention that u can use the external clock upto 40Mhz.
and hence i am using external oscillator as a Ext clock in EC mode...

any way my code is working now..
if u need it, let me know..

TIA,
Tom
 

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