Freescale Semiconductor HCS08 Series, Справочное руководство

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MC9S08JS16 MCU Series Reference Manual, Rev. 4
Freescale Semiconductor 79
Chapter 6
Parallel Input/Output
6.1 Introduction
This chapter explains software controls related to parallel input/output (I/O). The MC9S08JS16 has two
I/O ports which include a total of 14 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 the I/O pins are shared with on-chip peripheral functions, as shown in Table 2-1 . The peripheral
modules have priority over the I/Os, so when a peripheral is enabled, the I/O functions are disabled.
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 pins are configured as inputs (PTxDDn = 0). The pin control functions for each pin
are configured as follows: slew rate control enabled (PTxSEn = 1), low drive strength selected (PTxDSn
= 0), and internal pullups disabled (PTxPEn = 0).
NOTE
To avoid extra current drain from floating input pins, the user’s 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.
NOTE
When PTB0 is configured as output pin, it’s open-drain output.
6.2 Port Data and Data Direction
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.