ST72561 datasheet(98/262 Pages) STMICROELECTRONICS

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ST72561

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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 2 input capture functions in the 8-bit tim-

er.

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 5).

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 (i.e.

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:

6. The ICiR register contains the free running

counter value which corresponds to the most

recent input capture.

7. The 2 input capture functions can be used

together even if the timer also uses the 2 output

compare functions.

8. 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 rou-

tine software needs to discard the unwanted

capture interrupt. This can be done by checking

the ICF1 and ICF2 flags and resetting them

both.

9. In One pulse Mode and PWM mode only Input

Capture 2 can be used.

10.The alternate inputs (ICAP1 & ICAP2) are

always directly connected to the timer. So any

transitions 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 interrupt can be generated if the user tog-

gles the output pin and if the ICIE bit is set.

11.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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