ST92F120 datasheet(135/324 Pages) STMICROELECTRONICS

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EXTENDED FUNCTION TIMER (EFT)

10.3 EXTENDED FUNCTION TIMER (EFT)

10.3.1 Introduction

The timer consists of a 16-bit free-running counter

driven by a programmable prescaler.

It may be used for a variety of purposes, including

pulse length measurement of up to two input sig-

nals (

input capture) or generation of up to two out-

put waveforms (

output compare and PWM).

Pulse lengths and waveform periods can be mod-

ulated from a few microseconds to several milli-

seconds using the timer prescaler and the INTCLK

prescaler.

10.3.2 Main Features

Programmable prescaler: INTCLK divided

by 2, 4 or 8.

Overflow

status

flag

and

maskable

interrupts

External clock input (must be at least 4 times

slower than the INTCLK clock speed) with

the choice of active edge

Output compare functions with:

– 2 dedicated 16-bit registers

– 2 dedicated programmable signals

– 2 dedicated status flags

– 1 dedicated maskable interrupt

Input capture functions with

– 2 dedicated 16-bit registers

– 2 dedicated active edge selection signals

– 2 dedicated status flags

– 1 dedicated maskable interrupt

Pulse width modulation mode (PWM)

One pulse mode

5 alternate functions on I/O ports

Global timer interrupt (EFTI) mapped on

external interrupt channel

The Block Diagram is shown in Figure 73.

Table 27. EFT Pin Naming Conventions

10.3.3 Functional Description

10.3.3.1 Counter

The principal block of the Programmable Timer is

a 16-bit free running counter and its associated

16-bit registers:

Counter Registers

– Counter High Register (CHR) is the most sig-

nificant byte (MSB).

– Counter Low Register (CLR) is the least sig-

nificant byte (LSB).

Alternate Counter Registers

– Alternate Counter High Register (ACHR) is the

most significant byte (MSB).

– Alternate Counter Low Register (ACLR) is the

least significant byte (LSB).

These two read-only 16-bit registers contain the

same value but with the difference that reading the

ACLR register does not clear the TOF bit (overflow

flag), (see note page 137).

Writing in the CLR register or ACLR register resets

the free running counter to the FFFCh value.

The timer clock depends on the clock control bits

of the CR2 register, as illustrated in Table 28. The

value in the counter register repeats every

131.072, 262.144 or 524.288 INTCLK cycles de-

pending on the CC1 and CC0 bits.

Function

EFT0

EFT1

Input Capture 1 - ICAP1

ICAPA0

ICAPA1

Input Capture 2 - ICAP2

ICAPB0

ICAPB1

Output Compare 1 -

OCMP1

OCMPA0

OCMPA1

Output Compare 2 -

OCMP2

OCMPB0

OCMPB1

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