ST7FLCD1 datasheet(83/95 Pages) STMICROELECTRONICS

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ST7FLCD1

Infrared Preprocessor (IFR)

The Infrared Preprocessor measures the intervals between 2 adjacent edges of a serial input.

15.1

Main Features

● Interval measurement between 2 edges (Time Base = 12.5 kHz) @ fCPU = 8 MHz

● Choice of active edge

● Glitch filter

● Overflow detection (20.4 ms = 255/12.5 kHz)

● Maskable interrupt

15.2

Functional Description

The IR Preprocessor measures the interval between two adjacent edges of the IFR input signal.

The POSED and NEGED bits determine if the intervals of interest involve:

● consecutive positive edges,

● negative edges,

● or any pair of edges as described in Table 30.

The measurement is a count resulting from a 12.5 kHz clock. Therefore, any pulse width that is less

than 80 µs cannot be detected.

Whenever an edge of the specified polarity is detected, the count accumulated since the previously

detected edge is latched into the IFRDR register, an interrupt is generated and the counter is reset.

If an edge is not detected within 20.4 ms (fCPU = 8 MHz) and the count reaches its maximum value

of 255, it is latched immediately. The internal interrupt flag and also an internal overflow flag are set.

The latch content remains unchanged as long as the overflow flag is set.

The count stored in the latch register is overwritten in case the microcontroller fails to execute the

read before the next edge. Writing to the IFRDR register clears the interrupt and internal overflow

flag.

Figure 43: IFR Block Diagram

Filter Pulse

Edge Detection

8-bit Counter

8-bit Latch

FLSEL POSED NEGED

Interrupt

Clock Generation

12.5 kHz

IFR

fCPU

ITE

IFRCR

IFRDR

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