Alternate Function Configuration; Figure 20. Output Configuration; Figure 21. Alternate Function Configuration - ST STM32F412 Reference Manual

General-purpose I/Os (GPIO)
Read
Write
Read/write
7.3.11

Alternate function configuration

When the I/O port is programmed as alternate function:
•
The output buffer can be configured as open-drain or push-pull
•
The output buffer is driven by the signal 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 AHB1
clock cycle
•
A read access to the input data register gets the I/O state
Figure 21
To on-chip
peripheral
Read
Write
Read/write
From on-chip
peripheral
176/1163

Figure 20. Output configuration

Input driver
Output driver
shows the Alternate function configuration of the I/O port bit.

Figure 21. Alternate function configuration

Alternate function input
Alternate function output
on
TTL Schmitt
trigger
Output
control
V
on
TTL Schmitt
trigger
Input driver
Output driver
Output
control
RM0402 Rev 6
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
on/off
on/off
V
DD
P-MOS
V
N-MOS
push-pull or
V
SS
open-drain
RM0402
V
DD
protection
diode
I/O pin
protection
diode
V
SS
ai15941b
V
DD
DD
protection
diode
Pull
up
I/O pin
protection
Pull
down
diode
V
SS
SS
ai15942b