AN2281 datasheet(10/38 Pages) STMICROELECTRONICS

Il numero della parte	AN2281

Spiegazioni elettronici	Low cost self-synchronizing PMAC motor drive using ST7FLITE35

PDF	38 Pages

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Produttore elettronici	STMICROELECTRONICS [STMicroelectronics]

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10 / 38 page

Implementation on the ST7LITE35 microcontroller

AN2281

10/38

When an input capture occurs, the ICF bit is set and the LTICR register contains the MSB of

Counter 1. An interrupt is generated if the ICIE bit is set.

3.3

Lite timer configuration for measuring the Hall sensor period

As mentioned in the previous paragraph, the LTICR register can be used to latch Counter 1

every time an edge is detected on the LTIC pin. This characteristic of the Lite Timer,

together with the possibility of generating an interrupt when the upcounter overflows (LTTB1

Interrupt), allows you to precisely measure the semi-period of the Hall sensor signal.

Based on Figure 7, it is possible to draw the following mathematical relationship:

where tH represents the Hall sensor signal period, Capture 1 and Capture 2 indicate the

values of Counter 1 at the edges of the Hall sensor signal and N is the number of LTTB1

interrupt events between the two Hall sensor output transitions taken into account.

Figure 7.

Hall sensor signal semi-period measuring (N>0)

(3.3)

fOSC

= ((250-Capture 1)+Capture 2+250*(N-1))*

N>0

LTTB1 Int

Capture 2

LTIC Int

Capture 1

Hall sensor

output

Counter 1

249

LTTB1 Int

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