Hi, I'm observing greater than expected frequency calibration error with some PIC16LF88's - wondering what other peoples experiences are. I'm using the internal RC oscillator running at a nominal 8MHz, supply is 5V. Tested at a fairly stable room temperature (~22 deg C) I get the following frequency outputs (1ms timer interrupt toggles an output pin) from 5 different chips... 501.5Hz 519.0Hz 505.5Hz 497.0Hz 522.5Hz In this test my counter reload may not have been set for exactly 500Hz, but each of the above was tested with the same code, same temperature. I calculate a variation of around +/-2.5% from these results, ie. 5% between the two worst cases, the rest being somewhere between these two extremes and presumably closer to the correct frequency. What I was hoping for was something more like what the data sheet says - typically +/-1% accuracy at 25 deg C, max +/-2% for Vdd = 4.5 - 5.5V (DS30487C page 174). The only thing I can think of takes my test outside of the data sheet spec's is that I'm using LF chips which have the same spec as above but at 2.7 - 3.3V, and I'm running them at 5V. Perhaps that's it. I'm doing async comms between two PIC's at 19200 baud, and the variation above is enough to give me problems. Matching two PIC's from the above test means comms works well, even with considerable temperature differences - but it's a pain. I know I can calibrate using the OSCTUNE register, but would prefer not to as this would be a real pain when the design goes into production. I may add temperature compensation using OSCTUNE as I have a temperature sensor fairly close to the chip, but still the initial accuracy is a problem. I'm wondering about the factory calibration - there's no explanation of it in the data sheet, so presumably it can't be overwritten or erased in any way. I believe it's different to other PIC's where the factory calibration value had to be read & written in the user program somehow. Comments welcomed. -- Brent Brown, Electronic Design Solutions 16 English Street, St Andrews, Hamilton 3200, New Zealand Ph: +64 7 849 0069 Fax: +64 7 849 0071 Cell: 027 433 4069 eMail: brent.brown@clear.net.nz -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist