ST72754 datasheet(45/144 Pages) STMICROELECTRONICS

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16-BIT TIMER (Cont’d)

4.3.3.3 Input Capture

In this section, the index,

i, may be 1 or 2.

The two input capture 16-bit registers (IC1R and

IC2R) are used to latch the value of the free

running counter after a transition detected by the

ICAP

i pin (see figure 5).

i Rregister is a read-only register.

The active transition is software programmable

through the IEDG

i bit of the Control Register (CRi).

Timing resolution is one count of the free running

counter: (

fCPU/(CC1.CC0)).

Procedure

To use the input capture function select the

following in the CR2 register:

– Select the timer clock (CC1-CC0) (see Table 15

Clock Control Bits).

– Select the edge of the active transition on the

ICAP2 pin with the IEDG2 bit.

And select the following in the CR1 register:

– Set the ICIE bit to generate an interrupt after an

input capture.

– Select the edge of the active transition on the

ICAP1 pin with the IEDG1 bit.

When an input capture occurs:

– ICF

i bit is set.

– The IC

iR register contains the value of the free

running counter on the active transition on the

ICAP

i pin (see Figure 32).

– A timer interrupt is generated if the ICIE bit is set

and the I bit is cleared in the CC register. Other-

wise, the interrupt remains pending until both

conditions become true.

Clearing the Input Capture interrupt request is

done by:

1. Reading the SR register while the ICF

i bit is set.

2. An access (read or write) to the IC

iLR register.

After reading the IC

iHR register, transfer of input

capture data is inhibited until the IC

iLR register is

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