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16-BIT TIMING OPERATIONS USING ST7262 OR ST7263B MCUs

Figure 11 shows the normal behaviour of the input capture routine: each rising edge is de-

tected and the input capture interrupt routine is executed after the T0 delay. In this case the

period measurement operation can be easily done.

Figure 11. Case 1: Interrupt routine execution shorter than period to be measured

T: Period of the external signal to be measured

The minimum period that can measured depends strongly on the number of rising edges

during the interrupt routine execution.

A single rising edge during the execution of the interrupt routine does not corrupt the meas-

urement value and the period measurement operation can be achieved successfully (Figure

12).

Figure 12. Case 2: Interrupt routine execution longer than period to be measured

T: Period of the external signal to be measured

However, any additional rising edge leads to a corrupted measurement. As shown in Figure

12, the second rising edge is ignored, in fact before executing the input capture interrupt trig-

gered by the second rising edge, a third one occurs and overwrites the previous ICxR value.

For this reason the period measurement operation result is corrupted

(result = 2 * T).

T

T

T

T