Table of Contents
Advertisement
Notes
PES4T4 User Manual
®
Introduction
The PES4T4 has five 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, each
GPIO pin is shared with another on-chip function. The GPIO Function (GPIOFUNC) register determines
whether a GPIO bit operates as a general purpose I/O or as the specified alternate function.
Alternate
GPIO
Function
Pin
Pin Name
0
PE2RSTN
Reset output for downstream port 2
1
PE4RSTN
Reset output for downstream port 4
2
IOEXPINTN0
SMBus I/O expander interrupt 0
7
GPEN
General purpose event output
9
PE3RSTN
Reset output for downstream port 3
Table 5.1 General Purpose I/O Pin 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 128 ns 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. 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
PES4T4.
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.
GPIOFUNC
0
0
1
GPIO Pin Configured as an Input
When configured as an input in the GPIOCFG register and as a GPIO function in the GPIOFUNC
register, the GPIO pin is sampled and registered in the GPIOD register. The value of the input pin can be
determined at any time by reading the GPIOD register. Note that the value in this register corresponds to
the value of the pin irrespective of whether the pin is configured as a GPIO input, GPIO output, or alternate
function.
General Purpose
Inputs/Outputs
Alternate Function Description
GPIOCFG
0
1
don't care
Table 5.2 GPIO Pin Configuration
5 - 1
Chapter 5
Alternate
Function
Pin Type
Output
Output
Input
Output
Output
Pin Function
GPIO input
GPIO output
Alternate function
February 1, 2011
Advertisement
Table of Contents
