MC9S08QE16CLC Datasheet, PDF (85/350 Pages) Freescale Semiconductor, Inc – Low-power wireless applications, Gas, water and heater meters

Chapter 6 
Parallel Input/Output
6.1 Introduction
This chapter explains software controls related to parallel input/output (I/O). The MC9S08AC60 Series
has seven I/O ports which include a total of up to 54 general-purpose I/O pins. See Chapter 2, “Pins and
Connections” for more information about the logic and hardware aspects of these pins.
Many of these pins are shared with on-chip peripherals such as timer systems, communication systems, or
keyboard interrupts. When these other modules are not controlling the port pins, they revert to
general-purpose I/O control.
NOTE
Not all general-purpose I/O pins are available on all packages. To avoid
extra current drain from floating input pins, the user’s reset initialization
routine in the application program should either enable on-chip pullup
devices or change the direction of unconnected pins to outputs so the pins
do not float.
6.2 Pin Descriptions
The MC9S08AC60 Series has a total of 54 parallel I/O pins in seven ports (PTA–PTG). Not all pins are
bonded out in all packages. Consult the pin assignment in Chapter 2, “Pins and Connections,” for available
parallel I/O pins. All of these pins are available for general-purpose I/O when they are not used by other
on-chip peripheral systems.
After reset, the shared peripheral functions are disabled so that the pins are controlled by the parallel I/O.
All of the parallel I/O are configured as inputs (PTxDDn = 0). The pin control functions for each pin are
configured as follows: slew rate control disabled (PTxSEn = 0), low drive strength selected (PTxDSn = 0),
and internal pullups disabled (PTxPEn = 0).
6.3 Parallel I/O Control
Reading and writing of parallel I/O is done through the port data registers. The direction, input or output,
is controlled through the port data direction registers. The parallel I/O port function for an individual pin
is illustrated in the block diagram below.
MC9S08AC60 Series Data Sheet, Rev. 3
Freescale Semiconductor
85