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

1.3 AVERAGING AND GLITCH ALGORITHM

This algorithm an added feature to section1.2. When the 50 Hz source has noise or spikes,

this algorithm helps to prevent a wrong measurement of the reference signal. If you develop a

permanent hardware circuit to generate the 50 Hz signal, then it may contain noise signals as

well as glitches or spikes. This algorithm is a must in this case.

This software uses 12 bytes of RAM and takes 325 ms (one loop to find the average of 8 sam-

ples) to find the deviation fraction. The flowchart shows how this algorithm works.

Figure 3. Average and Glitch Algorithm Flowchart

yes

?

capture_range

sample = (+/-)10% of

First sample of capture counter is stored (capture_range)

for glitch filtering

Initialisation of TIMER A capture and variables

Check

no

Average

Internal RC deviation fraction = Average Capture Counter / Calculated (Ideal) Capture Counter

yes

?

over

8 samples

Is

no

(Figure 2)

START

Capture counter measurement