HC705RC17GRSSLASHD datasheet(59/126 Pages) NXP

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MC68HC705RC17 — Rev. 2.0

General Release Specification

Core Timer

General Release Specification — MC68HC705RC17

Section 8. Core Timer

8.1 Contents

8.2

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59

8.3

Core Timer Control and Status Register. . . . . . . . . . . . . . . . . .61

8.4

Core Timer Counter Register . . . . . . . . . . . . . . . . . . . . . . . . . .63

8.5

Computer Operating Properly (COP) Reset . . . . . . . . . . . . . . .63

8.6

Timer During Wait Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64

8.2 Introduction

The core timer for this device is a 14-stage multifunctional ripple counter.

Features include timer overflow, power-on reset (POR), real-time

interrupt (RTI), and COP watchdog timer.

As seen in Figure 8-1, the internal peripheral clock is divided by four,

and then drives an 8-bit ripple counter. The value of this 8-bit ripple

counter can be read by the CPU at any time by accessing the core timer

counter register (CTCR) at address $09. A timer overflow function is

implemented on the last stage of this counter, giving a possible interrupt

rate of the internal peripheral clock(E)/1024. This point is then followed

by three more stages, with the resulting clock (E/4096) driving the real-

time interrupt circuit (RTI). The RTI circuit consists of three divider

stages with a one-of-four selector. The output of the RTI circuit is further

divided by eight to drive the mask optional COP watchdog timer circuit.

The RTI rate selector bits and the RTI and CTOF enable bits and flags

are located in the timer control and status register at location $08.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

HC705RC17GRS/D Datasheet(PDF) 59 Page - NXP Semiconductors