Internal Oscillator PIC16F877A

sinan · Guest

Hi,

1)when using internal oscillator, do we still need an external clock?

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

With an internal oscillator you don't need an external clock. Only one of the two clock sources can be active at the same time.

The PIC6F877A does not have an internal oscillator.

sinan · Guest

We are using PIC16F877A not 6F877A. We checked the datasheet for 16F, and it says there is internal oscillator.

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

sinan · Guest

Thank you very much for helping me out.

Also, if you want to operate in XT mode with 2MHz, do we need to suply external 2Mhz oscillator and set #use delay(clock=2Mhz) or do we need to supply external 20Mhz oscillator and set #use delay(clock=2Mhz) . So basically, my question is do we have to use 20Mhz external clock?

Thanks again

Guest · Posted: Wed Apr 15, 2009 7:26 pm

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

The external crystal should have the same frequency as declared in the delay statement.

Set the XT fuse for the 2MHz crystal or HS for a 20MHz crystal.

Guest · Posted: Wed Apr 15, 2009 7:36 pm

Thanks very very much for your answers.

So I am using 2Mhz external crystal. In my code I set

#fuses XT

In the CCS program, Do I also change the Configuration Bits accordingly for the Oscillator. My TA told me not to change it from HS.

So if your fuse is in XT in the code, do you also alter the configuration bits?

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

The XT fuse sets the correct Config bits in the HEX file when the
program is compiled. The XT fuse controls the Config Bits for the
oscillator setting.