EUSART and Internal Oscillator

[Franck26]

Hello everybody,
I was wondering if it's crazy to use the EUSART with the internal Oscillator...

I want to make a communication between a 16F688 and a computer through the RS232 port @ 19200 baud.

16F688 datasheet specified the internal oscillator at 1%.
Is it enough accurate for my application?

Is there someone who have already tried this?

Thanks for any reply.

Franck.

[Ken Johnson]

This should work - generally you need about 3% for serial comms to work ok. Beware, though:

I did have a problem with an RS-485 network where several "slaves" would respond in a time slot. The time slots were too short and too close together, and would sometimes overlap due to the internal oscillator variation.

But, 2 devices should be able to talk ok.

Ken

[SherpaDoug]

Check out the clock accuracy plots at the back of the data sheet. There is usually a "sweet spot" at 5V and 25 degrees C where the accuracy is 1%. At other voltages and temperatures the accuracy gets much worse. A project may work fine on the bench but quit in the field when the temperature changes. In theory 8 bit serial comms can take up to 5% error, the worst case sum of the PIC error and the error of the PC or whatever is on the other end of the wire. But in practice it is good the try to keep the total error less than 3%.
_________________
The search for better is endless. Instead simply find very good and get the job done.

[asmboy]

i use the 16f887 and '886 all the time with int clock - at 19200 over a wide temkp range and have never had a customer complaint about flaky serial performance
YOU CAN DO THISD - ITS IS OK!!

[Franck26]

Thanks everybody for your answer,
It's true that the internal oscillator is specified at 2% between 0 and 85°c instead of 1%...

I think I will use the different advices of all of you: I'm going to leave a footprint for an oscillator on my board and if there is a poblem, I will put the appropriate quartz...

Thanks again,
Franck.