PIC12F675, accuracy of baud rate with Internal Oscillator

[Bruce]

The internal oscillator is just not a good choice for anything timing cricital. It's an RC oscillator, and the frequency will change as temperature, humidity, and several other factors change.

If you need reliable serial communications use an external oscillator.

I have used various PIC's in serial applications with the internal osc, and it does work, but it's never been reliable under varying conditions with the internal RC oscillator.

[Chris Mayhew]

The internal oscillator is just not a good choice for anything timing cricital. It's an RC oscillator, and the frequency will change as temperature, humidity, and several other factors change.

If you need reliable serial communications use an external oscillator.

I have used various PIC's in serial applications with the internal osc, and it does work, but it's never been reliable under varying conditions with the internal RC oscillator.

Hi Bruce

Thanks for your feedback.

As I don't have enough I/O's to add an XTAL I think an alternative solution might be to reconfigure the hardware and use SHIFTOUT. I have looked, but can find any info that says it can't be done and since a PIC can send SEROUT direct over a cable (I'll be using about 2 metres) I'm assuming the same would apply to SHIFTOUT (putting in some current limiting resistors).

Another alternative might be to use PULSOUT and COUNT but that could get a bit messy.....

I should have also pointed out that I was intending to send 1 to 3 bytes of data every 10 to 15 seconds between 2 PIC's over about 2 metres of cable. One PIC would be potted and put into a water tank, while the other would be in free air. The one in free air would certainly be subject to wide temp changes. This would be even more of a reason NOT to use SEROUT2.

[mister_e]

by the amount of data you send, you can use a low baudrate, let's say 300 baud and should be fair enough with INTRC at almost any temperature.