AN2710 datasheet(17/30 Pages) STMICROELECTRONICS

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AN2710

STR75x general-purpose I/O ports (GPIO)

17/30

2.1.5

Alternate function configuration

When the I/O port is programmed as an alternate function:

●

The output buffer is turned on in open drain or push-pull configuration

●

The output buffer is driven by the signal coming from the peripheral (alternate function

out)

●

The Schmitt trigger input is activated

●

The analog switch is disabled

●

The weak pull-up and pull-down resistors are disabled

●

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

cycle

●

A read access to the I/O Data register gets:

–

the output latch value in Push-Pull mode (which corresponds to the last data

written)

–

the input latch value in Open-Drain mode

Figure 10 shows the alternate function configuration of the I/O port bit.

Figure 10.

Alternate function configuration

2.1.6

Analog input configuration

When the I/O port is programmed as an analog input:

●

The output buffer is disabled

●

The Schmitt trigger input is de-activated, providing zero consumption for every analog

value of the I/O pin. The output of the Schmitt trigger is forced to a constant value (0).

●

The weak pull-up and pull-down resistors are disabled

●

The analog switch is enabled by the ADC each time a conversion is in progress

●

Read access to the I/O Data register gets the input latch value (0)

Figure 11 shows the high impedance-analog input configuration of the I/O port bit.

Alternate Function Output

Alternate Function Input

Push-pull or

open-drain

Read/write

From on-chip

peripheral

To on-chip

peripheral

Output

control

I/O pin

VDD_IO

VSS

TTL Schmitt

trigger

VSS

VDD_IO

Protection

diode

Protection

diode

Input driver

Output driver

P-MOS

N-MOS

ai14925

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