
RM0453 Rev 2
399/1454
RM0453
General-purpose I/Os (GPIO)
426
The figure below shows the output configuration of the I/O port bit.
Figure 46. Output configuration
10.3.11
Alternate function configuration
When the I/O port is programmed as alternate function, the following occurs:
•
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.
The figure below shows the alternate function configuration of the I/O port bit.
Figure 47. Alternate function configuration
Push-pull or
Open-drain
Output
control
V
DDIOx
V
SS
TTL Schmitt
trigger
on
Input driver
Output driver
P-MOS
N-MOS
Inpu
t dat
a
regis
ter
Outpu
t data regis
ter
Read/write
Read
Bi
t se
t/rese
t
regis
ter
s
Write
on/off
pull
pull
on/off
V
DDIOx
V
SS
V
SS
V
DDIOx
protection
diode
protection
diode
down
up
I/O pin
MS31478V1
MSv34756V2
Alternate function output
Alternate function input
push-pull or
open-drain
From on-chip
peripheral
To on-chip
peripheral
Output
control
VDD
VSS
TTL Schmitt
trigger
on
Input driver
Output driver
P-MOS
N-MOS
In
pu
t
d
ata
regi
s
te
r
Out
p
u
t
d
a
ta
regist
er
Read/write
Read
B
it
set/
re
set
regist
ers
Write
on/off
on/off
VDDIOx
VSS VSS
protection
diode
protection
diode
Pull
Pull
I/O pin
down
up
VDDIOx