MC68908GZ8MFJE Datasheet, PDF (155/314 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 13
Input/Output (I/O) Ports
13.1 Introduction
Bidirectional input-output (I/O) pins form five parallel ports. All I/O pins are programmable as inputs or
outputs. All individual bits within port A, port C, and port D are software configurable with pullup devices
if configured as input port bits. The pullup devices are automatically and dynamically disabled when a port
bit is switched to output mode.
13.2 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;
1. Configuring unused pins as inputs and enabling internal pull-ups;
1. 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.
Addr.
$0000
$0001
$0002
$0003
Register Name
Bit 7
6
5
4
3
Port A Data Register ^Read:
(PTA) Write:
See page 158. _Reset:
PTA7
PTA6
PTA5
PTA4
PTA3
Unaffected by reset
Port B Data Register ^Read:
(PTB) Write:
See page 160.
Reset:
PTB7
PTB6
PTB5
PTB4
PTB3
Unaffected by reset
Read: 1
Port C Data Register
(PTC) Write:
See page 162. _Reset:
PTC6
PTC5
PTC4
PTC3
Unaffected by reset
Port D Data Register ^Read:
(PTD) Write:
See page 164. _Reset:
PTD7
PTD6
PTD5
PTD4
PTD3
Unaffected by reset
= Unimplemented
Figure 13-1. I/O Port Register Summary
2
PTA2
PTB2
PTC2
PTD2
1
PTA1
PTB1
PTC1
PTD1
Bit 0
PTA0
PTB0
PTC0
PTD0
MC68HC908GZ16 • MC68HC908GZ8 Data Sheet, Rev. 4
Freescale Semiconductor
155