MC68HC908QL4 Datasheet, PDF (111/226 Pages) Motorola, Inc – Microcontrollers

Chapter 12
Input/Output Ports (PORTS)
12.1 Introduction
The MC68HC908QL4 has thirteen bidirectional input-output (I/O) pins and one input only pin. All I/O pins
are programmable as inputs or outputs.
12.2 Unused Pin Termination
Input pins and I/O port pins that are not used in the application must be terminated. This prevents excess
current caused by floating inputs, and enhances immunity during noise or transient events. Termination
methods include:
1. Configuring unused pins as outputs and driving high or low;
2. Configuring unused pins as inputs and enabling internal pull-ups;
3. Configuring unused pins as inputs and using external pull-up or pull-down resistors.
Never connect unused pins directly to V_DD or V_SS.
Since some general-purpose I/O pins are not available on all packages, these pins must be terminated
as well. Either method 1 or 2 above are appropriate.
12.3 Port A
Port A is an 6-bit special function port that shares its pins with the keyboard interrupt (KBI) module (see
Chapter 9 Keyboard Interrupt Module (KBI), the 2-channel timer interface module (TIM) (see Chapter 15
Timer Interface Module (TIM)), the 10-bit ADC (see Chapter 3 Analog-to-Digital Converter (ADC10)
Module), the external interrupt (IRQ) pin (see Chapter 8 External Interrupt (IRQ)), the reset (RST) pin
enabled using a configuration register (see Chapter 5 Configuration Register (CONFIG)) and the
oscillator pins (see Chapter 11 Oscillator Module (OSC)).
Each port A pin also has a software configurable pullup/down device if the corresponding port pin is
configured as an input port.
PTA2 is input only.
NOTE
When the IRQ function is enabled in the configuration register 2
(CONFIG2), bit 2 of the port A data register (PTA) will always read a logic 0.
In this case, the BIH and BIL instructions can be used to read the logic level
on the PTA2 pin. When the IRQ function is disabled, these instructions will
behave as if the PTA2 pin is a logic 1. However, reading bit 2 of PTA will
read the actual logic level on the pin.
MC68HC908QL4 Data Sheet, Rev. 7
Freescale Semiconductor
111