MC908GR32AVFAE Datasheet, PDF (131/314 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 12
Input/Output (I/O) Ports
12.1 Introduction
Bidirectional input-output (I/O) pins form seven parallel ports. All I/O pins are programmable as inputs or
outputs. All individual bits within port A, port C, port D and port F 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.
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.
Addr.
$0000
$0001
$0002
Register Name
Bit 7
6
5
4
3
2
Read:
Port A Data Register
(PTA) Write:
See page 135.
Reset:
Read:
Port B Data Register
(PTB) Write:
See page 138.
Reset:
PTA7
PTB7
PTA6
PTB6
PTA5
PTB5
PTA4
PTA3
Unaffected by reset
PTB4
PTB3
Unaffected by reset
PTA2
PTB2
Read: 1
Port C Data Register
(PTC) Write:
See page 140.
Reset:
PTC6
PTC5
PTC4
PTC3
Unaffected by reset
PTC2
= Unimplemented
Figure 12-1. I/O Port Register Summary (Sheet 1 of 3)
1
PTA1
PTB1
PTC1
Bit 0
PTA0
PTB0
PTC0
MC68HC908GR60A • MC68HC908GR48A • MC68HC908GR32A Data Sheet, Rev. 5
Freescale Semiconductor
131