Internal Oscillator Sources

[electronicsman]

I am going through the dsPIC33 family datasheet oscillator section and the first line states
The dsPIC33/PIC24 family oscillator system includes these characteristics:
• External and internal oscillator sources.

The question comes is generally every one will go for external oscillator, when should one go for internal oscillator? Is it for safety or some other back up in case the external oscillator fails? Please advise.

 

[KlausST]

Hi,

Benefit of internal oscillator:
* no extra part cost
* no extra board space
* no extra assembling cost

Drawback:
* not that accurate
* not that stable
* not available for external circuitry (depending on microcontroller)
* one can not choose any desired frequency

Klaus

 

[electronicsman]

Hi,

Benefit of internal oscillator:
* no extra part cost
* no extra board space
* no extra assembling cost

Drawback:
* not that accurate
* not that stable
* not available for external circuitry (depending on microcontroller)
* one can not choose any desired frequency

Klaus

Thank you for the reply. Few more clarifications once the micro starts let us say it has to read Register "R" to decide to select internal or external oscillator. During this time it runs on which oscillator?

I think this is done during device programming. Am I correct for microchip, i am not sure about the other micro controllers.

 

[FvM]

PIC24 and other controllers have features like automatic clock switchover, you want to read the manual. The start-up clock selection is set in nonvolatile configuration fuses.

Internal fast RC oscillator has about 1% accuracy and is good for many applications, e.g. standard UART communication, but not for full speed USB.

 

[paulfjujo]

hello,

on a 16F1847 , **broken link removed**

6.0 REFERENCE CLOCK MODULE
The reference clock module is controlled by the
CLKRCON register (Register 6-1) and is enabled when
setting the CLKREN bit. To output the divided clock
signal to the CLKR port pin, the CLKROE bit must be
set. The CLKRDIV<2:0> bits enable the selection of
eight different clock divider options. The
CLKRDC<1:0> bits can be used to modify the duty
cycle of the output clock(1). The CLKRSLR bit controls
slew rate limiting.

so, you can have 8 different FOSC values on Pin RA6, independantly of FOSC used for MCU
so i think some PIC24 must have this option ...