ST52F510 datasheet(51/106 Pages) STMICROELECTRONICS

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ST52F510/F513/F514

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7.5 Alternate Functions

The Alternate Function allows the pins to be

connected with the peripheral signals or NMI. Not

all

Port

pins

have

Alternate

Function

associated.

A Configuration Register (PORT_x_AF) for each

Port is used to switch from the Digital I/O function

or the Alternate Function.

Some pins can have two Alternate Functions: one

input function and one output function. To switch

between the two functions, the PORT_x_AF must

be configured in Alternate Function mode and the

PORT_x_DDR Configuration Register must be

switched in Input mode or in Output mode.

NMI is considered an Alternate Function. For this

reason

NMI

interrupt

request

can’t

generated unless the PA7 pin is configured in

Alternate Function and in one of the Input modes.

Figure 7.3 Port Pin Architecture

When an on-chip peripheral is configured to use a

pin, the correct I/O mode of the related pin should

be selected by selecting one of the appropriate

modes. See the Registers description in order to

obtain the right configurations.Some peripherals,

as for example the I2C peripheral, directly drive the

pin configuration according to the current function,

overriding the user configuration.

7.6 Register Description

In order to configure the Port’s pins, the three

Configuration

Registers

PORT_x_PULLUP,

PORT_x_OR

and

PORT_x_DDR

must

configured. The combination of these three

registers

determine

the

pin’s

configuration,

according to the scheme shown in Table 7.1.

In order to select between the digital functions or

Alternate functions PORT_x_AF register must be

configured. Each bit of the configuration registers

configures the pin of the corresponding position

(example: PORT_A_DDR bit 5 configures the pin

PA5).

CONF. REG.

FILE

ALTERNATE

FUNCTION

INTERRUPT

POLARITY

IRQ

TO INPUT

Vdd

DIGITAL

PORT PIN

INT

SEL

ENABLE

DATA

CONF. REG.

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