IDT 89HPES24N3A, User Manual

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Notes
PES24N3A User Manual 5 - 1 April 10, 2008
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Chapter 5
General Purpose I/O
Introduction
The PES24N3A has 8 General Purpose I/O (GPIO) pins that may be individually configured as: general
purpose inputs, general purpose outputs, or alternate functions. GPIO pins are controlled by the General
Purpose I/O Function (GPIOFUNC), General Purpose I/O Configuration (GPIOCFG), and General Purpose
I/O Data (GPIOD) registers in the upstream port’s PCI configuration space. As shown in Table 5.1, some
GPIO pins are shared with other on-chip functions. The GPIO Function (GPIOFUNC) register determines
whether a GPIO bit operates as a general purpose I/O or as the specified alternate function.
After reset, all GPIO pins default to the GPIO input function. GPIO pins configured as GPIO inputs are
sampled no more frequently than once every 128ns and may be treated as asynchronous inputs.
When a GPIO pin is configured to use the GPIO function, the unneeded alternate function associated
with the pin is held in an inactive state by internal logic.
Note: Care should be exercised when configuring the GPIO pins as outputs since an incorrect
configuration could cause damage to external components as well as the PES24N3A.
GPIO Configuration
Associated with each GPIO pin is a bit in the GPIOFUNC, GPIOCFG and GPIOD registers. Table 5.2
summarizes the configuration of GPIO pins.
GPIO
Pin
Alternate
Function
Pin Name
Alternate Function Description
Alternate
Function
Pin Type
0 P2RSTN Reset output for downstream port 2 Output
1 P4RSTN Reset output for downstream port 4 Output
2 IOEXPINTN0 SMBus I/O expander interrupt 0 Input
4 IOEXPINTN2 SMBus I/O expander interrupt 2 Input
7 GPEN General purpose event output Output
Table 5.1 General Purpose I/O Pin Alternate Function
GPIOFUNC GPIOCFG Pin Function
0 0 GPIO input
0 1 GPIO output
1 don’t care Alternate function
Table 5.2 GPIO Pin Configuration