HCS08 datasheet(24/316 Pages) NXP

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Chapter 1 Device Overview

MC9S08SG8 MCU Series Data Sheet, Rev. 8

Freescale Semiconductor

1.3

System Clock Distribution

Figure 1-2 shows a simplified clock connection diagram. Some modules in the MCU have selectable clock

inputs as shown. The clock inputs to the modules indicate the clock(s) that are used to drive the module

function.

The following defines the clocks used in this MCU:

•

BUSCLK — The frequency of the bus is always half of ICSOUT.

•

ICSOUT — Primary output of the ICS and is twice the bus frequency.

•

ICSLCLK — Development tools can select this clock source to speed up BDC communications in

systems where the bus clock is configured to run at a very slow frequency.

•

ICSERCLK — External reference clock can be selected as the RTC clock source and as the

alternate clock for the ADC module.

•

ICSIRCLK — Internal reference clock can be selected as the RTC clock source.

•

ICSFFCLK — Fixed frequency clock can be selected as clock source for the TPM1, TPM2 and

MTIM modules.

•

LPOCLK — Independent 1-kHz clock source that can be selected as the clock source for the COP

and RTC modules.

•

TCLK — External input clock source for TPM1, TPM2 and MTIM and is referenced as TPMCLK

in TPM chapters.

Figure 1-2. System Clock Distribution Diagram

TPM1

TPM2

MTIM

SCI

BDC

CPU

ADC

IIC

FLASH

ICS

ICSOUT

2 BUSCLK

ICSLCLK

ICSERCLK

COP

* The fixed frequency clock (FFCLK) is internally

synchronized to the bus clock and must not exceed one

half of the bus clock frequency.

FLASH has frequency

requirements for program

and erase operation. See



the electricals appendix

for details.

ADC has min and max



frequency requirements.



See the ADC chapter

and electricals appendix

for details.

XOSC

EXTAL

XTAL

SPI

FFCLK*

ICSFFCLK

RTC

1 kHZ

LPO

TCLK

ICSIRCLK

2

SYNC*

LPOCLK

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