IDT PCI Express 89HPES32NT24xG2, User Manual, Page: 245 / 744

Notes
PES32NT24xG2 User Manual 13 - 1 January 30, 2013
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Chapter 13
General Purpose I/O
Overview
The switch 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), General Purpose I/O
Data (GPIOD), and General Purpose I/O Alternate Function Select (GPIOAFSEL) register.
After a switch fundamental reset, all GPIO pins default to a GPIO input function. GPIO pins configured
as GPIO inputs are double-clocked and sampled no more frequently than once every 128 ns. Thus, they
may be treated as asynchronous inputs. Associated with each GPIO pin are alternate functions.
Note: Care should be exercised when configuring GPIO pins as outputs since an incorrect configura-
tion could cause damage to the switch and external components.
GPIO Configuration
Associated with each GPIO pin is a bit in the GPIOFUNC, GPIOCFG and GPIOD registers. Table 13.1
summarizes the configuration of GPIO pins.
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. 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.
Output
When configured as an output in the GPIOCFG register and as a GPIO function in the GPIOFUNC
register, the value in the corresponding bit position of the GPIOD register is driven on the pin.
– System designers should treat the GPIO outputs as asynchronous outputs.
The actual value of the output pin may be determined by reading the GPIOD register.
Alternate Function
Each GPIO pin has two alternate functions. An alternate function associated with a specific GPIO pin is
selected by the corresponding field in the GPIOAFSEL register. The alternate functions associated with
each GPIO pin are listed in Table 13.2.
GPIOFUNC GPIOCFG Pin Functionality
0 0 GPIO input
0 1 GPIO output
1 don’t care Alternate function
Table 13.1 GPIO Pin Configuration