68HC05C5 datasheet(39/58 Pages) FREESCALE

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Page 33

Section 6: Timer

MC68HC05C5 Specification Rev. 1.2

SECTION 6

TIMER

6.1

INTRODUCTION

The timer consists of a 16-bit, software-programmable counter driven by a fixed divide-

by-four prescaler. This timer can be used for many purposes, including input waveform

measurements while simultaneously generating an output waveform. Pulse widths can

vary from several microseconds to many seconds. Refer to Figure 6-1 for a timer block

diagram.

Because the timer has a 16-bit architecture, each specific functional segment (capability)

is represented by two registers. These registers contain the high and low byte of that

functional segment. Generally, accessing the low byte of a specific timer function allows

full control of that function; however, an access of the high byte inhibits that specific timer

function until the low byte is also accessed.

Note: The I bit in the CCR should be set while manipulating both the high and low byte

Input

Capture

Clock

Internal Bus

Output

Compare

High

Byte

Low

Byte

$16

$17

∏∏∏

Internal

Processor

16-Bit Free

Running

Counter

Alternate

8-Bit

Buffer

High

Byte

Low

Byte

$1A

$1B

$18

$19

High

Byte

Low

Byte

$14

$15

Output

Compare

Circuit

Overflow

Detect

Circuit

Edge

Detect

Circuit

Timer

Status

Reg.

ICF OCF TOF $13

ICIE

IEDG OLVL

Output

Level

Reg.

RESET

Timer

Control

Reg.

$12

Output

Level

(TCMP)

Interrupt

Circuit

TOIE

OCIE

Edge

Input

(TCAP)

CLK

Figure 6-1: Timer Block Diagram

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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