ST92F124 datasheet(170/426 Pages) STMICROELECTRONICS

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EXTENDED FUNCTION TIMER (EFT)

EXTENDED FUNCTION TIMER (Cont’d)

10.3.3.3 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 run-

ning counter after a transition detected by the

ICAPi pin (see figure 5).

ICi Rregister is a read-only register.

The active transition is software programmable

through the IEDGi bit of the Control Register (CRi).

Timing resolution is one count of the free running

counter: (INTCLK/CC[1:0]).

Procedure

To use the input capture function select the follow-

ing in the CR2 register:

– Select the timer clock (CC[1:0] (see Table 36).

– Select the edge of the active transition on the

ICAP2 pin with the IEDG2 bit, if ICAP2 is active.

And select the following in the CR1/CR3 register:

– To enable both ICAP1 & ICAP2 interrupts, set

the ICIE bit in the CR1 register (in this case, the

IC1IE & IC2IE enable bits are not significant).

To enable only one ICAP interrupt, reset the ICIE

bit and set the IC1IE (or IC2IE) bit.

Note: If ICIE is reset and both IC1IE & IC2IE are

set, both interrupts are enabled.

In all cases, set the EFTIS bit to enable timer in-

terrupts globally

– Select the edge of the active transition on the

ICAP1 pin with the IEDG1 bit if ICAP1 is active.

When an input capture occurs:

– ICFi bit is set.

– The ICiR register contains the value of the free

running counter on the active transition on the

ICAPi pin (see Figure 96).

– A timer interrupt is generated under the following

two conditions :

1. If the ICIE bit (for both ICAP1 & ICAP2) and

the EFTIS bit are set.

Note: If the ICIE bit is set, the status of the

IC1IE/IC2IE bits in the CR3 register is not sig-

nificant.

2. If the ICIE bit is reset and the IC1IE and /or

IC2IE bits are set and the EFTIS bit is set.

Otherwise, the interrupt remains pending until

the related enable bits are set.

Clearing the Input Capture interrupt request is

done by:

1. An access (read or write) to the SR register

while the ICFi bit is set.

2. An access (read or write) to the ICiLR register.

Note: After reading the ICiHR register, transfer of

input capture data is inhibited until the ICiLR regis-

ter is also read.

The ICiR register always contains the free running

counter value which corresponds to the most re-

cent input capture.

MS Byte

LS Byte

ICiRICiHR

ICiLR

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