HCS08 datasheet(83/290 Pages) MOTOROLA

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Data Sheet — MC9S08GB60/D V1.5

MOTOROLA

MC9S08GB/GT

6.1 Introduction

Figure 6-3 is a top-level diagram that shows the functional organization of the internal clock generation

(ICG) module. This section includes a general description and a feature list.

Figure 6-3 ICG Block Diagram

The ICG provides multiple options for clock sources. This offers a user great flexibility when making

choices between cost, precision, current draw, and performance. As seen in Figure 6-3, the ICG consists

of four functional blocks. Each of these is briefly described here and then in more detail in a later section.

•

Oscillator block — The oscillator block provides means for connecting an external crystal or

resonator. Two frequency ranges are software selectable to allow optimal startup and stability.

Alternatively, the oscillator block can be used to route an external square wave to the system clock.

External sources can provide a very precise clock source.

•

Internal reference generator — The internal reference generator consists of two controlled clock

sources. One is designed to be approximately 8 MHz and can be selected as a local clock for the

background debug controller. The other internal reference clock source is typically 243 kHz and

can be trimmed for finer accuracy via software when a precise timed event is input to the MCU.

This provides a highly reliable, low-cost clock source.

OSCILLATOR (OSC)

FREQUENCY

INTERNAL

EXTAL

XTAL

REFERENCE

GENERATORS

CLOCK

SELECT

8 MHz

IRG

LOSS OF LOCK

AND CLOCK DETECTOR

LOCKED

LOOP (FLL)

FIXED

CLOCK

SELECT

ICGOUT

TYP 243 kHz

ICGLCLK

ICG

FFE

VDDA

V SSA

(SEE NOTE 2)

DCO

WITH EXTERNAL REF

SELECT

REF

SELECT

LOCAL CLOCK FOR OPTIONAL USE WITH BDC

OUTPUT

CLOCK

SELECT

ICGDCLK

ICGERCLK

ICGIRCLK

NOTES:

1. See chip level clock routing diagram for specific use of ICGOUT, FFE, ICGLCLK, ICGERCLK

2. Not all HCS08 microcontrollers have unique supply pins for the ICG. See the device pin assignments in

the Pins and Connections section for specifics.

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