STR71x & STR73x I/O ports

AN2710

8/30

1.2.1

Alternate function I/O (AF)

The alternate functions for each pin are listed in the datasheet. Configuring a port bit as

alternate function will disconnect the output latch and connect the pin to the output signal of

an on-chip peripheral.

●

For alternate function inputs, the port must be configured in Input mode and the input

pin must be driven externally.

Note:

It is also possible to emulate the AFI input pin by firmware by programming the GPIO

controller. In this case, the port should be configured in Alternate Function Output mode.

And obviously, the corresponding port should not be driven externally as it will be driven by

the firmware using the GPIO controller.

●

For AF output or input-output, the port bit must be in AF configuration.

External interrupts/wakeup lines

Some ports have external interrupt capability (see datasheet). To use external interrupts, the

port must be configured in input mode. For more information on interrupts and wakeup lines,

refer to the reference manual.

1.2.2

Input configuration

When the I/O port is programmed as Input:

●

The output buffer is forced tristate

●

The data present on the I/O pin are sampled into the input latch with every clock cycle

●

A read access to the Data register gets the value in the input latch.

Figure 2 shows the input configuration of the I/O port bit.

Figure 2.

Input configuration

1.

For STR73x only.

I/O pin

Analog input

Alternate function (OUT)

Alternate function (IN)

Tristate

TTL

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