Input Configuration; Figure 15. Input Floating/Pull Up/Pull Down Configurations - ST STM32F101 series Reference Manual

General-purpose and alternate-function I/Os (GPIOs and AFIOs)
9.1.7

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 15 on page 163
Read
Write
Read/write
1. V is a potential specific to five-volt tolerant I/Os and different from V
DD_FT
163/1128
shows the Input Configuration of the I/O Port bit.

Figure 15. Input floating/pull up/pull down configurations

input driver
output driver
on/off
on
TTL Schmitt
trigger
on/off
.
DD
DocID13902 Rev 15
V
DD
or V
V
DD
protection
diode
V
SS
protection
diode
V
SS
RM0008
(1)
DD_FT
I/O pin
ai14783