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pic 16f877a with 20MHz clock

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vipinms_85

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can any one tell me how to configure pic 16f877a with 20MHz crystal ......my code is working with 4 MHz but not in 20MHz...... plz help me
 

Hi,

Here, there are two different case..
1. Your code does not work properly at 20 MHz despite of it works with at 4 MHz clock.
2. Execution does not start in generally on your 16F877A.

If case 1 happens, you need to review your code. Serial communication or timing dependent functions might not work properly when clock frequency changed but necessary timing and settings were ignored.

If case 2 happens, I can think as first that you did not set your 16F877A to HS clock speed.. You have to select from your programmer (or in your code HS clock options)

Regards.
 

What is your code ? Where is you code ?

Have you set the fuse bits correctly ?
 

If you r using mplab select configure>>configuration bits and select "HS" (high Speed) from the list, see the picture below
 

You have to change the fuse bit from XT_OSC to HS_OSC

bye
 

You should give more information.

1. Complier name?
 

Hi,

Can some1 tell me how to calculate the counter rate of Timer1 of pic16f877? It seems that the value changes with oscillator frequency. am using 4MHz crystal at the moment. But I need to know my current Timer1 counter rate as well as the value when the oscillator frequency is changed to 20MHz or something else.


Thanks.
 

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