
Clock and Phase Locked Loop Signals
56F807 Technical Data Technical Data, Rev. 15
Freescale Semiconductor
11
2.3   Clock and Phase Locked Loop Signals
2.4   Address, Data, and Bus Control Signals
Table 2-5 PLL and Clock
No. of 
Pins
Signal 
Name
Signal
Type
State During
Reset
Signal Description
1
EXTAL
Input
Input
External Crystal Oscillator Input
—This input should be connected to 
an 8MHz external crystal or ceramic resonator. For more information, 
please refer to 
Section 3.4
.
1
XTAL
Input/
Output
Chip-driven
Crystal Oscillator Output
—This output should be connected to an 
8MHz external crystal or ceramic resonator. For more information, please 
refer to 
Section 3.4
.
This pin can also be connected to an external clock source. For more 
information, please refer to 
Section 3.4.2
.
1
CLKO
Output
Chip-driven
Clock Output
—This pin outputs a buffered clock signal. By programming 
the CLKOSEL[4:0] bits in the CLKO Select Register (CLKOSR), the user 
can select between outputting a version of the signal applied to XTAL and 
a version of the device’s master clock at the output of the PLL. The clock 
frequency on this pin can also be disabled by programming the 
CLKOSEL[4:0] bits in CLKOSR.
Table 2-6 Address Bus Signals
No. of 
Pins
Signal
Name
Signal
Type
State During 
Reset
Signal Description
6
A0–A5
Output
Tri-stated
Address Bus
—A0–A5 specify the address for external Program or 
Data memory accesses. 
2
A6–A7
GPIOE2-
GPIOE3
Output
Input/O
utput
Tri-stated
Input
Address Bus
—A6–A7 specify the address for external Program or 
Data memory accesses. 
Port E GPIO
—These two General Purpose I/O (GPIO) pins can 
individually be programmed as input or output pins. 
After reset, the default state is Address Bus. 
8
A8–A15
GPIOA0-
GPIOA7
Output
Input/O
utput
Tri-stated
Input
Address Bus
—A8–A15 specify the address for external Program or 
Data memory accesses. 
Port A GPIO
—These eight General Purpose I/O (GPIO) pins can be 
individually programmed as input or output pins. 
After reset, the default state is Address Bus.