ST STM32F301 6 Series Reference Manual page 132

General-purpose I/Os (GPIO)
Read
Write
Read/write
8.3.10 Output configuration
When the I/O port is programmed as output:
•
The output buffer is enabled:
–
–
• The Schmitt trigger input is activated
•
The pull-up and pull-down resistors are activated depending on the value in the
GPIOx_PUPDR register
•
The data present on the I/O pin are sampled into the input data register every AHB
clock cycle
•
A read access to the input data register gets the I/O state
•
A read access to the output data register gets the last written value
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Figure 16. Input floating / pull up / pull down configurations
input driver
output driver
Open drain mode: a "0" in the output register activates the N-MOS whereas 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 whereas a "1" in
the output register activates the P-MOS
on
TTL Schmitt
trigger
RM0366 Rev 5
RM0366
V DD
V DD
on/off
protection
diode
pull
up
I/O pin
on/off
protection
pull
diode
down
V SS
V SS
ai15940b