IDT 89HPES12T3G2, Preliminary User'S Manual

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Notes
PES12T3G2 User Manual 4 - 1 January 28, 2013
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Chapter 4
General Purpose I/O
Introduction
The PES12T3G2 has 9 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. Table 4.1, shows GPIO
pins that are shared with other on-chip functions. The GPIO Function (GPIOFUNC) register controls
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 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
PES12T3G2.
GPIO Configuration
Associated with each GPIO pin is a bit in the GPIOFUNC, GPIOCFG and GPIOD registers. Table 4.2
summarizes the configuration of GPIO pins.
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.
GPIO
Pin
Alternate
Function
Pin Name
Alternate Function
Description
Alternate
Function
Pin Type
0 PE2RSTN Reset output for downstream port 2 Output
1 PE4RSTN 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 4.1 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 4.2 GPIO Pin Configuration