LAN8804D datasheet(47/89 Pages) MICROCHIP

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LAN8804D

DS00003591K-page 47

The INT_N buffer type is selectable between open-drain and push-pull and is configured by the INT Buffer Type field in

the Output Control register. The default is open-drain.

The Intr Polarity Invert bit in the Control register sets the interrupt level to active high or active low. The default is active

low. If the buffer type is set to open-drain, the polarity is forced to be active low.

5.16

GPIOs

The General Purpose I/Os (GPIOs) consist of 24 programmable input/output pins that are shared with other pins. These

pins are individually configurable via the GPIO registers.

GPIOs support the following functions:

• Software-readable GPIO. The GPIO is an input and its value can be directly read via the GPIO Data register. In

addition, these GPIOs can also be configured to generate interrupts.

• Software-writable GPIO. The GPIO is an output and its value can be directly set via the GPIO Data register.

• GPIO Alternate Function. The GPIO pin is shared with some other function. Depending on the alternate function,

the GPIO pin may be either an input or output. If the GPIO pin is an input, it can still be configured to perform any

GPIO input function in addition to the alternate function.

For a pin to function as its GPIO, the GPIO must be enabled via the corresponding bit in the GPIO Enable Registers.

When configured as an input, via the GPIO Direction register (GPIO_DIR1 or GPIO_DIR2), the pin’s pull-up is enabled.

Each bit in the GPIO Data Registers reflects the current state of the corresponding GPIO input.

When configured as an output, the output buffer type is selected by the corresponding bit in the GPIO Buffer Type Reg-

isters. Push/pull and open-drain output buffers are supported for each GPIO.

• When functioning as an open-drain driver, the GPIO output pin is driven low when the corresponding bit in the

GPIO Data Registers is cleared to ‘0’ and is not driven when set to ‘1’.

• When functioning as a push/pull output, the GPIO output pin is driven low or high by the corresponding bit in the

GPIO Data Registers.

When a GPIO is set to an output, the pin’s pull-up is disabled, however the pin’s input buffer remains enabled. A read

of the GPIO Data Registers returns the state of the GPIO inputs (not the previous values written to these registers).

5.16.1

GPIO ALTERNATE FUNCTIONS

Many GPIOs have the ability to be used as an alternate function. Once enabled as a GPIO, the alternate function is

selected by the bits in the GPIO Alternate Function Select Registers.

The alternate function buffer type is still selected via the GPIO Buffer Type Registers. If the alternate function is a Port

LED and the GPIO Buffer Type is open-drain, the output buffer will automatically select between open-source and open-

drain based on the applicable LED Polarity.

Alternate Functions input pins can be read by software via the GPIO Data register, can generate GPIO Interrupts.

Table 5-7 describes the alternate function mappings. Alternate functions are each described fully in Section 3.0, "Pin

Descriptions and Configuration".

Note:

Extreme care must be taken on strap input pins that may be used for General Purpose Inputs. The General

Purpose Inputs must be conditioned or otherwise disabled such that they do not drive incorrect strap input

values during the strap loading time.

TABLE 5-7:

GPIO ALTERNATE FUNCTIONS

GPIO

Alternate Function

Configuration Strap

Comments

GPIO23

SOF3

——

GPIO22

—

GPIO21

SOF1

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