
MC9S08GT16A/GT8A Data Sheet, Rev. 1
Freescale Semiconductor
125
Chapter 9
Internal Clock Generator (S08ICGV4)
9.1
Introduction
The MC9S08GT16A/GT8A microcontroller provides one internal clock generation (ICG) module to
create the system bus frequency. All functions described in this section are available on the
MC9S08GT16A/GT8A microcontroller. The EXTAL and XTAL pins share port G bits 2 and 1,
respectively. Analog supply lines VDDA and VSSA are internally derived from the MCU’s VDD and VSS
Figure 9-1. System Clock Distribution Diagram
NOTE
Freescale Semiconductor programs a factory trim value for ICGTRM into
the FLASH location $FFBE (NVICGTRM). Leaving this address for the
ICGTRM value also allows debugger and programmer vendors to perform
a manual trim operation and store the resultant ICGTRM value into
NVICGTRM for users to access at a later time. The value in NVICGTRM
is not automatically loaded and therefore must be copied into ICGTTRM by
user code.
ATD has min and max
frequency requirements. See
FLASH has frequency
requirements for program
and erase operation.
* ICGLCLK is the alternate BDC clock source for the MC9S08GT16A/GT8A.
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
÷2
COP