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8-BIT TIMER (Cont’d)

10.5.3.2 Input Capture

In this section, the index, i, may be 1 or 2 because

there are two input capture functions in the 8-bit

timer.

The two 8-bit input capture registers (IC1R and

IC2R) are used to latch the value of the free run-

ning counter after a transition is detected on the

ICAPi pin (see Figure 63).

ICiR register is a read-only register.

The active transition is software programmable

through the IEDGi bit of Control Registers (CRi).

Timing resolution is one count of the free running

counter (see Table 19 Clock Control Bits).

Procedure:

To use the input capture function select the follow-

ing in the CR2 register:

– Select the timer clock (CC[1:0]) (see Table 19

Clock Control Bits).

– Select the edge of the active transition on the

ICAP2 pin with the IEDG2 bit (the ICAP2 pin

must be configured as floating input or input with

pull-up without interrupt if this configuration is

available).

And select the following in the CR1 register:

– Set the ICIE bit to generate an interrupt after an

input capture coming from either the ICAP1 pin

or the ICAP2 pin

– Select the edge of the active transition on the

ICAP1 pin with the IEDG1 bit (the ICAP1 pin

must be configured as floating input or input with

pull-up without interrupt if this configuration is

available).

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 64).

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

and the interrrupt mask is cleared in the CC reg-

ister. Otherwise, the interrupt remains pending

until both conditions become true.

Clearing the Input Capture interrupt request (that

is, clearing the ICFi bit) is done in two steps:

1. Reading the SR register while the ICFi bit is set.

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

Notes:

1. The ICiR register contains the free running

counter value which corresponds to the most re-

cent input capture.

2. The two input capture functions can be used to-

gether even if the timer also uses the two output

compare functions.

3. Once the ICIE bit is set both input capture fea-

tures may trigger interrupt requests. If only one is

needed in the application, the interrupt routine

software needs to discard the unwanted capture

interrupt. This can be done by checking the ICF1

and ICF2 flags and resetting them both.

4. In One pulse Mode and PWM mode only Input

Capture 2 can be used.

5. The alternate inputs (ICAP1 and ICAP2) are al-

ways directly connected to the timer. So any tran-

sitions on these pins activates the input capture

function.

Moreover if one of the ICAPi pins is configured as

an input and the second one as an output, an inter-

rupt can be generated if the user toggles the output

pin and if the ICIE bit is set.

6. The TOF bit can be used with interrupt genera-

tion in order to measure events that go beyond the

timer range (FFh).

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