Datasheet

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 V
DDA
and V
SSA
are internally derived from the MCU’s V
DD
and V
SS
pins. Electrical parametric data for the ICG may be found in Appendix A, “Electrical Characteristics.”
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
Chapter 14, “Analog-to-Digital Convert-
er (S08ATDV3),” and Appendix A,
“Electrical Characteristics.”
FLASH has frequency
requirements for program
and erase operation.
See Appendix A, “Electrical
Characteristics.”
* 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