Input Configuration; Output Configuration; Figure 12. Input Floating/Pull Up/Pull Down Configurations - ST STM32F102 Series Reference Manual

RM0008
7.1.7

Input configuration

When the I/O Port is programmed as Input:
●
The Output Buffer is disabled
●
The Schmitt Trigger Input is activated
●
The weak pull-up and pull-down resistors are activated or not depending on input
configuration (pull-up, pull-down or floating):
●
The data present on the I/O pin is sampled into the Input Data Register every APB2
clock cycle
● A read access to the Input Data Register obtains the I/O State.
The Figure 12 on page 101

Figure 12. Input floating/pull up/pull down configurations

Read
Write
Read/write
1. V
DD_FT
7.1.8

Output configuration

When the I/O Port is programmed as Output:
●
The Output Buffer is enabled:
–
–
●
The Schmitt Trigger Input is activated.
● The weak pull-up and pull-down resistors are disabled.
●
The data present on the I/O pin is sampled into the Input Data Register every APB2
clock cycle
●
A read access to the Input Data Register gets the I/O state in open drain mode
●
A read access to the Output Data register gets the last written value in Push-Pull mode
The Figure 13 on page 102
General-purpose and alternate-function I/Os (GPIOs and AFIOs)
shows the Input Configuration of the I/O Port bit.
input driver
output driver
is a potential specific to five-volt tolerant I/Os and different from V
Open Drain Mode: A "0" in the Output register activates the N-MOS while a "1" in
the Output register leaves the port in Hi-Z. (the P-MOS is never activated)
Push-Pull Mode: A "0" in the Output register activates the N-MOS while a "1" in the
Output register activates the P-MOS.
shows the Output configuration of the I/O Port bit.
V
DD
on/off
on
TTL Schmitt
trigger
on/off
V
SS
or V
V
DD DD_FT
protection
diode
I/O pin
protection
diode
V
SS
.
DD
(1)
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