ST STM32L4+ Series Reference Manual page 339

RM0432
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
Figure 29
Figure 28. Output configuration
Read
shows the Alternate function configuration of the I/O port bit.
Figure 29. Alternate function configuration
Alternate function input
To on-chip
peripheral
Read
Write
Read/write
From on-chip
Alternate function output
peripheral
on
TTL Schmitt
trigger
Input driver
Output driver
Output
control
on
TTL Schmitt
trigger
Input driver
Output driver
Output
control
RM0432 Rev 6
General-purpose I/Os (GPIO)
V
DDIOx
on/off
pull
up
V
DDIOx
on/off
P-MOS
pull
down
V
SS
N-MOS
Push-pull or
V
SS Open-drain
VDDIOx VDDIOx
on/off
Pull
up
on/off
V
DD
Pull
P-MOS
down
V
V
SS
SS
N-MOS
push-pull or
V
SS
open-drain
V
DDIOx
protection
diode
I/O pin
protection
diode
V
SS
MS31478V1
protection
diode
I/O pin
protection
diode
MSv34756V1
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