Serial differences between f628 and f628A

[Melanie]

Let's put it this way - If the world was flat, you're sailing right on the edge.

Use a crystal or resonator... you've been lucky so far... but it's just run out!

[das1818]

Thank You. The PCB is so full and OSC1 and OSC2 are being used, maybe it's time for a bigger chip and new PCB layout.

[Melanie]

And a Crystal or Resonator!

[tenaja]

A lot of it depends on your volume, too. For just a couple boards you use yourself, just manually tweak the osctune register to adjust the oscillator. (Assuming they will see a consistent temperature.)

If you are shipping them out, and if you have code space, you could put in an oscillator calibration routine. You'll need a reference, though--either an on-board crystal, RTC, or incoming serial data.

You also might be able to "guess" at the osctune value by reading the pic errors in reception. Look it up in the datasheet.

But the easiest is to add a real crystal.

[mister_e]

... and as long as the PIC has a OSCTUNE register

Still not a fan of internal OSC for serial communication myself... even if the more recent PIC show a better accuracy... it's still a RC OSC.