ST STM32F301 6 Series Reference Manual page 133

RM0366
Figure 17
Read
Write
Read/write
8.3.11 Alternate function configuration
When the I/O port is programmed as alternate function:
•
The output buffer can be configured in open-drain or push-pull mode
• The output buffer is driven by the signals coming from the peripheral (transmitter
enable and data)
•
The Schmitt trigger input is activated
•
The weak pull-up and pull-down resistors are activated or not 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
shows the output configuration of the I/O port bit.
Figure 17. Output configuration
Input driver
Output driver
on
TTL Schmitt
trigger
Output
control
V
RM0366 Rev 5
General-purpose I/Os (GPIO)
V
DD
on/off
pull
up
V
DD
on/off
P-MOS
pull
down
V
SS
N-MOS
Push-pull or
SS Open-drain
V
DD
protection
diode
I/O pin
protection
diode
V
SS
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