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ACCURATE TIMEBASE FOR LOW-COST ST7 APPLICATIONS WITH INTERNAL RC...

This fraction can be used to calibrate the other peripheral parameters to add precision to the

the timing calculations.

If a Mains Supply is used as an external source, this solution works for an European Supply

(50 Hz)). If a US supply (60 Hz) is used, the calculated Capture Counter will be 0x411B to find

the fraction for internal RC deviation.

A software routine is developed to find this fraction and utilize it to calibrate the peripheral pa-

rameters. this routine is included in the application. The basic software takes less than 30ms

to find the fraction, which gives the deviation of real RC frequency with reference to the da-

tasheet frequency. This application includes a glitch filter algorithm and also takes the average

of 8 samples for finding the fraction. The basic algorithm and the average + glitch algorithms

are described in the next chapters. The software takes less than 325ms with the averaging

and glitch algorithms.

This routine execution time includes the 8 capture elapsed times, waiting times for the cap-

tures and the loop calculations inside the routine. The routine execution time is affected mostly

by the capture waiting times. This routine will run in the background of the main application, so

MCU can run other tasks during this 30ms (basic software algorithm) or 325ms (for average

and glitch algorithm) period.

InternalRCDeviationFraction

MeasuredCaptureCounter

CalculatedCaptureCounter

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