mc9s08qg4 Freescale Semiconductor, Inc, mc9s08qg4 Datasheet - Page 77

• Manufacturer Part Number: mc9s08qg4
• Description: Hcs08 Microcontrollers Microcontroller Family
• Manufacturer: Freescale Semiconductor, Inc

Chapter 6
Parallel Input/Output Control
This section explains software controls related to parallel input/output (I/O) and pin control. The
MC9S08QG8 has two parallel I/O ports which include a total of 12 I/O pins, one output-only pin and one
input-only pin. See
assignments and external hardware considerations of these pins. Not all pins are available on all devices
of the MC9S08QG8/4 Family; see
device.
All of these I/O pins are shared with on-chip peripheral functions as shown in
modules have priority over the I/Os so that when a peripheral is enabled, the I/O functions associated with
the shared pins are disabled. After reset, the shared peripheral functions are disabled so that the pins are
controlled by the I/O. All of the I/Os are configured as inputs (PTxDDn = 0) with pullup devices disabled
(PTxPEn = 0), except for output-only pin PTA4 which defaults to the BKGD/MS pin.
6.1
Reading and writing of parallel I/Os is performed through the port data registers. The direction, either 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 shown in
Freescale Semiconductor
Port Data and Data Direction
Not all general-purpose I/O pins are available on all packages. To avoid
extra current drain from floating input pins, the user reset initialization
routine in the application program must either enable on-chip pullup devices
or change the direction of unconnected pins to outputs so the pins do not
float.
Section Chapter 2, “External Signal
MC9S08QG8 and MC9S08QG4 Data Sheet, Rev. 4
Table 1-1
for the number of general-purpose pins available on your
NOTE
Description,” for more information about pin
Figure
6-1.
Table
2-2. The peripheral
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