ST7260 datasheet(43/117 Pages) STMICROELECTRONICS

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ST7260

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16-BIT TIMER (Cont’d)

11.2.3.3 Input Capture

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

there are two input capture functions in the 16-bit

timer.

The two 16-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 28).

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: (

fCPU/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 17,

"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 ICAP1pin must

be configured as floating input or input with pull-

up without interrupt if this configuration is availa-

ble).

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 29).

– 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 (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 ICiLR register.

Notes:

1. After reading the ICiHR register, transfer of

input capture data is inhibited and ICFi will

never be set until the ICiLR register is also

read.

2. The ICiR register contains the free running

counter value which corresponds to the most

recent input capture.

3. The two input capture functions can be used

together even if the timer also uses the two out-

put compare functions.

4. In One Pulse mode and PWM mode only Input

Capture 2 can be used.

5. The alternate inputs (ICAP1 and 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.

This can be avoided if the input capture func-

tion i is disabled by reading the ICiHR (see note

1).

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

tion in order to measure events that go beyond

the timer range (FFFFh).

MS Byte

LS Byte

ICiR

ICiHR

ICiLR

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