AN2710 datasheet(16/30 Pages) STMICROELECTRONICS

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STR75x general-purpose I/O ports (GPIO)

AN2710

16/30

2.1.4

Output configuration

When the I/O port is programmed as an output:

●

The output buffer is enabled:

–

Open Drain mode: a “0” in the output latch activates the N-MOS while a “1” in the

output latch leaves the port in Hi-Z (the P-MOS is never activated)

–

Push-Pull mode: a “0” in the output latch activates the N-MOS while a “1” in the

output latch activates the P-MOS

●

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 is 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 9 shows the output configuration of the I/O port bit.

Figure 9.

Output configuration

Push-pull or

open-drain

Output

control

I/O pin

VDD_IO

VSS

TTL Schmitt

trigger

VSS

VDD_IO

Protection

diode

Protection

diode

Input driver

Output driver

Read/write

P-MOS

N-MOS

ai14924

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