68HC05PL4 datasheet(52/98 Pages) FREESCALE

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GENERAL RELEASE SPECIFICATION

April 30, 1998

16-BIT PROGRAMMABLE TIMER

MC68HC05PL4

9-2

REV 2.0

The basis of the capture/compare Timer is a 16-bit free-running counter which

increases in count with each internal bus clock cycle. The counter is the timing ref-

erence for the input capture and output compare functions. The input capture and

output compare functions provide a means to latch the times at which external

events occur, to measure input waveforms, and to generate output waveforms and

timing delays. Software can read the value in the 16-bit free-running counter at

any time without affect the counter sequence.

Because of the 16-bit timer architecture, the I/O registers for the input capture and

output compare functions are pairs of 8-bit registers. Each register pair contains

the high and low byte of that function. Generally, accessing the low byte of a spe-

ci c timer function allows full control of that function; however, an access of the

high byte inhibits that speci c timer function until the lo w byte is also accessed.

Because the counter is 16 bits long and preceded by a x ed divide-by-four pres-

caler, the counter rolls over every 262,144 internal clock cycles. Timer resolution

with a 4 MHz crystal oscillator is 2 microsecond/count.

The interrupt capability, the input capture edge, and the output compare state are

controlled by the timer control register (TCR) located at $0012 and the status of

the interrupt ags can be read from the timer status register (TSR) located at

$0013.

9.1

TIMER REGISTERS (TMRH, TMRL)

The functional block diagram of the 16-bit free-running timer counter and timer

registers is shown in Figure 9-2. The timer registers include a transparent buffer

latch on the LSB of the 16-bit timer counter.

Figure 9-2. Timer Counter and Register Block Diagram

TMRH ($0018)

TMR LSB

16-BIT COUNTER

÷ 4

INTERNAL

(XTAL ÷2)

TIMER CONTROL REG.

TIMER

REQUEST

OVERFLOW (TOF)

RESET

CLOCK

INTERRUPT

TMRL ($0019)

TIMER STATUS REG.

$0012

$0013

INTERNAL

($FFFC)

DATA

READ

TMRH

READ

TMRL

READ

LATCH

BUS

Freescale Semiconductor, Inc.

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Go to: www.freescale.com

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