HC805K3GRSSLASHD datasheet(71/119 Pages) NXP

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MC68HC805K3 — Rev. 1.0

8-Bit Timer

General Release Specification — MC68HC805K3

Section 8. 8-Bit Timer

8.1 Contents

8.2

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71

8.3

Timer Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73

8.3.1

Timer Counter Register (TCNTR) $09 . . . . . . . . . . . . . . . .73

8.3.2

Timer Status/Control Register (TSCR) $08. . . . . . . . . . . . .74

8.4

COP Watchdog Timer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76

8.5

Operating During Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . .76

8.2 Introduction

The timer for this device is an 8-bit ripple counter. The features include

timer overflow, power-on reset (POR), real time interrupt, and COP

watchdog timer. This timer is powered down in the stop mode to reduce

STOP IDD.

As shown in Figure 8-1, the timer is driven by the timer clock, NTF1,

divided by four (4). NTF1 has the same phase and frequency as the

processor bus clock, PH2, but is not stopped by the wait or halt modes.

This signal 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 timer

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

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

at the rate of fOP/1024. Two additional stages produce the POR function

at fOP/4064 or fOP/16, followed by two more stages, with the resulting

clock (fOP/16,384) driving the real time interrupt (RTI) circuit.

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 optional COP watchdog timer circuit, which can be enabled by a

mask option register bit. The RTI rate selector bits, and the RTI and TOF

enable bits and flags are located in the timer control and status register

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

HC805K3GRS/D Datasheet(PDF) 71 Page - NXP Semiconductors