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PIC18LF252 at 10MHz and 3.3V . possible?

 
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PIC18LF252 at 10MHz and 3.3V . possible?
PostPosted: Mon Feb 21, 2005 11:25 am     Reply with quote
hi,
it is possible what a PIC18LF252 running at 3.3V dont works properly
with a 10MHz quartz???
The same PIC works perfectly with 4MHz quartz..
A problem of THIS chip or i dont understood the microchip formula for
calculate the max freq. versus Vcc ???

thanks
regards
Mauro IK1WVQ
ckielstra



Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands

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PostPosted: Mon Feb 21, 2005 12:07 pm     Reply with quote
Have a look at the formula below figure 22-2 of the data sheet:

Quote:
Fmax = (16.36MHz/V) (Vddappmin - 2.0V) + 4MHz.


Running at 3.3V this gives an Fmax of 25.268MHz
10MHz shouldn't be a problem.

Check your '#fuse' settings:
- XT setting can be used from 0,1 to 4MHz
- HS setting is for 4MHz to 25MHz.
These settings where derived from table 22-4 in the datasheet.
rwyoung



Joined: 12 Nov 2003
Posts: 563
Location: Lawrence, KS USA

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PostPosted: Mon Feb 21, 2005 12:46 pm     Reply with quote
ckielstra wrote:
Have a look at the formula below figure 22-2 of the data sheet:

Quote:
Fmax = (16.36MHz/V) (Vddappmin - 2.0V) + 4MHz.


Running at 3.3V this gives an Fmax of 25.268MHz
10MHz shouldn't be a problem.

Check your '#fuse' settings:
- XT setting can be used from 0,1 to 4MHz
- HS setting is for 4MHz to 25MHz.
These settings where derived from table 22-4 in the datasheet.


Also, don't try to turn on the x4 PLL at 3.3V and 10MHz external crystal.

Study figure 22-2. It tells you graphically what you need to know. The equation below the graph is for Vdd between 4.2V and 2.0V and give the maximum operating frequency of the IC, not necessarily the maximum crystal you can use.
_________________
Rob Young
The Screw-Up Fairy may just visit you but he has crashed on my couch for the last month!
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