Post by thread:Internal oscilator calibration

How can the internal oscilator calibration on one of the 12C5xx pics can be verified? I have the original calibration value, but I would like to make sure it is right, because my application is timing critical. TIA Gabriel Gonzalez

You could get a short wave radio receiver and tune around 4 MHZ when the PIC is running to see if you can hear the oscillator. One can buy digitally-tuned short wave receivers that are fairly decent for between $100 to $200.00. Remember that the RC oscillators are the least stable of all the various designs of oscillator so if it is within a few kilohertz of 4 MHZ, it is as good as it is going to get. Chances are very good that tomorrow, given a little different temperature or power supply voltage, it will have drifted several more kilohertz. The world time and frequency stations definitely do not use RC oscillators for precise timing.:-) Martin McCormick

I would not rely on an internal RC oscillator calibrated or no for timing critical applications. Rich At 03:17 PM 2/25/98 -0600, you wrote: {Quote hidden}>How can the internal oscilator calibration on one of the 12C5xx pics can be >verified? > >I have the original calibration value, but I would like to make sure it is >right, because my application is timing critical. > >TIA > >Gabriel Gonzalez > > ========================================= = Abolish the Income Tax! Fire the IRS! = = http://www.nrst.org/ = =========================================

Calvin: Like most people said, the internal oscilator may not be a good choice because of the drift due to voltage and temperature changes. If you must use the internal oscillator, then depending on the application of the chip, you can add some code in your program to put the chip in a test mode by holding an input low at reset time and in the test mode you can just toggle one of the outputs at a fixed rate and measure it with a frequency counter. Shahid ---------- From: Calvin[SMTP:spam_OUTtgoTakeThisOuTCHIH1.TELMEX.NET.MX] Reply To: pic microcontroller discussion list Sent: Wednesday, February 25, 1998 4:17 PM To: .....PICLISTKILLspam@spam@MITVMA.MIT.EDU Subject: Internal oscilator calibration How can the internal oscilator calibration on one of the 12C5xx pics can be verified? I have the original calibration value, but I would like to make sure it is right, because my application is timing critical. TIA Gabriel Gonzalez

I am sorry for being ambiguous on my request. My application is not really that critical, it is for RS232 comms. But the real question should have been: How much can I trust the factory oscilator calibration for the 12C5xx PICS??? Gabriel {Original Message removed}

Once upon a time I saw a project where the guy said he was able to calibrate timings based on the internal oscillator in a 12C5xx chip, and that he was able to compensate for the typical RC drift you get with temperature change, voltage change, phase of the moon, etc. Is it actually possible to compensate for the RC drift in your code, or am I crazy? :-) Robert Powell Programmer/Analyst Hollywood Entertainment Wilsonville, OR (503)570-5307