68HC705SP7 datasheet(162/230 Pages) FREESCALE

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Programmable Timer

General Release Specification

MC68HC705JJ7/MC68HC705JP7 — Rev. 3.0

Programmable Timer

11.5 Input Capture Registers (ICRH and ICRL)

The input capture function is a means to record the time at which an

event occurs. The source of the event can be the change on an external

pin (PB3/AN3/TCAP) or the CPF2 flag bit of voltage comparator 2 in the

analog subsystem. The ICEN bit in the analog subsystem control

the input capture circuitry detects an active edge on the selected source,

it latches the contents of the free-running timer counter registers into the

input capture registers as shown in Figure 11-6.

NOTE:

Both the ICEN bit in the ACR and the IEDG bit in the TCR must be set

when using voltage comparator 2 to trigger the input capture function

Latching values into the input capture registers at successive edges of

the same polarity measures the period of the selected input signal.

Latching the counter values at successive edges of opposite polarity

measures the pulse width of the signal.

Figure 11-6. Timer Input Capture Block Diagram

ICRH ($0014)

16-BIT COUNTER

÷ 4

INTERNAL

(OSC

÷ 2)

TIMER CONTROL REG.

TIMER

REQUEST

INPUT CAPTURE (ICF)

RESET

CLOCK

INTERRUPT

ICRL ($0015)

TIMER STATUS REG.

$0012

$0013

INTERNAL

DATA

READ

ICRH

READ

ICRL

LATCH

BUS

EDGE

SELECT

& DETECT

LOGIC

PB3

AN3

TCAP

INPUT

SELECT

MUX

CPF2

FLAG

ICEN

CONTROL

BIT

FROM

ANALOG

SUBSYSTEM

INTERNAL

DATA

BUS

Freescale Semiconductor, Inc.

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