8-bit MicrocontrollersのトピックRe: Internal or external reference clock

Internal or external reference clock

jesortsan — Thu, 08 Mar 2007 19:34:04 GMT

Hi,

my future application (with a MC9S08DZ microcontroller) doesn't require almost any speed restriction.

For that reason, I think it's better to use the internal reference clock and so I can avoid an external circuit for a external oscillator.

What do you think about that? Am I correct or it's better to use always an external oscillator as a reference?

It's my first application and I'm not sure about some issues...

Thanks

Re: Internal or external reference clock

Lundin — Thu, 08 Mar 2007 19:50:03 GMT

Since you decided for DZ I have to assume that you plan to use CAN. If any serial bus like CAN or SCI is used, you will need an accurate oscillator to get the correct baudrates. For example, the baudrate for CAN is only allowed to be +- 0.4% faulty. This is impossible to achieve with the internal oscillator, since it isn't stable enough.

Re: Internal or external reference clock

stevo10 — Fri, 09 Mar 2007 16:46:31 GMT

It really depends on the application, its not always better to use an external as I'm sure you've got other factors out with perfomance to account for. Although you say you have no speed restrictions, how about the accuracy of your clock? External reference are generally more accurate.

With the internal reference you are able to trim the clock with the trim register and the fine trim bit in the MCGSC register - which will improve your accuracy.

I also agree with the comment above, if you are making use of the CAN module then an external would be the best option.

Re: Internal or external reference clock

jesortsan — Fri, 09 Mar 2007 16:54:04 GMT

I have no speed or accuracy restrictions, except the use of the CAN module. I'll choose the external clock option in order to comply with CAN requests.

Thanks for your indications