whats the crystal frequency range for PIC 18f452 ?

[bilal shareef]

I am working on PIC 18f452. and i want to know the maximum crystal frequency that can i use to get maximum speed ... Can i use 40Mhz crystal. ?

 

[hexreader]

See table 22-4 in the datasheet and check out the different oscillator modes to see which can be used with a crystal.

Maximum (2-pin) crystal frequency is 25MHz

Maximum external clock is 40MHz (such as from a 4-pin canned crystal oscillator module)


To get 40MHz processor clock from crystal, use 10MHz crystal and set configuration bits for HS-PLL mode

 

[wp100]

Hi,

Also see entry #4 in this post about 'activating' HSPLL mode on the 452 https://www.edaboard.com/threads/257730/

 

[furqankaimkhani]

You can use 40 MHz but the frequency is too much high. Why do you wish to have such high frequency?

 

[hexreader]

You can use 40 MHz but the frequency is too much high. Why do you wish to have such high frequency?

Let's turn the question around.....

Unless you are running from batteries and want to save power, why would anyone want to run at less than maximum frequency?

Maximum frequency means maximum processing power.

... and yes, I know, there are a few other reasons..

 

[bilal shareef]

From the data sheet of PIC18F452 ... i have found this
- DC - 40 MHz osc./clock input


can any body tell me how can i connect that 40Mhz crsytal.... in what configuration

 

[wp100]

From the data sheet of PIC18F452 ... i have found this
- DC - 40 MHz osc./clock input


can any body tell me how can i connect that 40Mhz crsytal.... in what configuration

Hi,

It does not say that - it can onyy use a crystal to a max of 25mhz using the HS config and connected as shown in Fig 2.1

The 40 Mhz input is when an external oscillator is providing a proper 40mhz square wave.
A Crystal does not provide a square wave, it needs the oscillator ciruitry in the Pic to produce a square wave, and the 452 circuity can only do up to 25 mhz.
See table 22-4 in the datasheet.

I assume you cannot get the 10mhz crystal to work with PLL to make 40 Mhz ?

Go back to basics and establish a reference point: -
Can you correctly flash a led for 1 sec on and 1 sec off using the 10meg crystal in HS mode ?

 

[hexreader]

From the data sheet of PIC18F452 ... i have found this
- DC - 40 MHz osc./clock input


can any body tell me how can i connect that 40Mhz crsytal.... in what configuration

Nowhere in this quote is the word "crystal" mentioned.

Please stop shouting at us and start reading the replies that you have been given.