AMD Elan SC520 - Chapter 23 Programmable Input;Output

Élan™SC520 Microcontroller User’s Manual 23-1
CHAPTER
23
PROGRAMMABLE INPUT/OUTPUT
23.1 OVERVIEW
The ÉlanSC520 microcontroller supports 32 programmable I/O signals (PIOs) that can be
used on the system board to monitor signals or control devices that are not handled by the
other functions in the ÉlanSC520 microcontroller. These signals can be programmed to be
inputs or to be driven out High or Low as outputs.
The PIO signals can be programmed for the following functions:
■ Read as inputs (default condition after reset)
■ Driven High or Low as an output
On the ÉlanSC520 microcontroller, all of the PIOs are shared with other functions that may
not be needed in every system design, e.g., GP bus signals. This is done to give system
designers the most flexibility. For clarity, throughout this document, the two functions
available on the PIO pins are distinguished from each other as the
PIO function and the
interface function .
Each of the PIO signals is terminated within the ÉlanSC520 microcontroller with either a
pullup or pulldown resistance. This feature makes system design easier by eliminating the
need for termination on the board. Each PIO signal is terminated according to the pin’s
interface function, i.e., a normally active Low signal will usually have a pullup to make it
inactive on reset. See the
Élan™SC520 Microcontroller Data Sheet , order #22003, for the
termination of each PIO signal.
23.2 BLOCK DIAGRAM
Figure 23-1 is a block diagram of the PIO feature. This structure is repeated for each of the
PIOs; only one example PIO is shown in the diagram.