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16-BIT TIMING OPERATIONS USING ST7262 OR ST7263B MCUs

1.1.1.2 Delay Compensation method

The software delay introduced by the interrupt routine should be taken into account otherwise

the measurement value can be corrupted. This happens if the ART counter rolls over from FFh

to 00h while software is storing the TBUCV value after a valid input capture interrupt. In this

case, the TBUCV is incremented and a wrong value occurs in the 8th bit of the 16-bit input

capture value.

The delay compensation method is described in the following flowchart (Figure 2).

The first step consists of transferring both TBU and ART values into temporary variables

(TmpTBU1, TmpART, TmpTBU2) to be used later on. Then in the second step we compare

TmpART and ICxR. There are two cases to be considered:

– TmpART >= ICRx: This means that the ART counter value was incremented by a few cycles

but has not yet reached the maximum value (FFh). In this case we use TmpTBU1.

– TmpART < ICRx:This means that the ART counter was incremented beyond the maximum

value and has been reset. This means we should decrement TmpTBU2 once to get the right

value of TBUCV.

Figure 2. TBU Delay Compensation flowchart

1.1.1.3 Example of an interrupt capture routine

The input capture interrupt routine given below can be used to get the precise value of the

input capture interrupt instant on ICAP1 pin. It can be used to detect a rising or falling edge de-

pending on the configured edge in ARTICSR.

.Inp_Cap_Routine

;----------------------------------------;

Ld A , TBUCV

;Load the TBU counter value

Interrupt From ICAP1 or ICAP2

TmpART >= ICxR

Read & Store the TBUCV in TmpTBU1

Read & Store the ARTCAR inTmpART

Read & Store the TBUCV in TmpTBU2

Yes

No

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