System Clock Distribution
MC9S08GB/GT Data Sheet, Rev. 2.3
Freescale Semiconductor
21
Table 1-2 lists the functional versions of the on-chip modules.
1.4
System Clock Distribution
Figure 1-3. System Clock Distribution Diagram
Some of the modules inside the MCU have clock source choices. Figure 1-3 shows a simplied clock
connection diagram. The ICG supplies the clock sources:
ICGOUT is an output of the ICG module. It is one of the following:
— The external crystal oscillator
— An external clock source
— The output of the digitally-controlled oscillator (DCO) in the frequency-locked loop
sub-module
Control bits inside the ICG determine which source is connected.
Table 1-2. Block Versions
Module
Version
Analog-to-Digital Converter (ATD)
3
Internal Clock Generator (ICG)
2
Inter-Integrated Circuit (IIC)
1
Keyboard Interrupt (KBI)
1
Serial Communications Interface (SCI)
1
Serial Peripheral Interface (SPI)
3
Timer Pulse-Width Modulator (TPM)
1
Central Processing Unit (CPU)
2
TPM1
TPM2
IIC1
SCI1
SCI2
SPI1
BDC
CPU
ATD1
RAM
FLASH
ICG
ICGOUT
÷2
FFE
SYSTEM
LOGIC
BUSCLK
ICGLCLK*
CONTROL
FIXED FREQ CLOCK (XCLK)
ICGERCLK
RTI
ATD has min and max
frequency requirements.
FLASH has frequency
requirements for program
and erase operation.
* ICGLCLK is the alternate BDC clock source for the MC9S08GB/GT.
÷2