DocID018909 Rev 11
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RM0090
General-purpose I/Os (GPIO)
290
Figure 29. Output configuration
8.3.11
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
shows the Alternate function configuration
of the I/O port bit.
Figure 30. Alternate function configuration
0USHPULLOR
/PENDRAIN
/UTPUT
CONTROL
6
$$
6
33
44,3CHMITT
TRIGGER
ON
)NPUTDRIVER
/UTPUTDRIVER
0-/3
.-/3
)NPU
T
DAT
A
R
EGIS
TER
/UTPU
T
D
ATA
REGIS
TER
2EADWRITE
2EAD
"I
TSE
TRESE
T
REGIS
TER
S
7RITE
ONOFF
PULL
PULL
ONOFF
6
$$
6
33
6
33
6
$$
PROTECTION
DIODE
PROTECTION
DIODE
DOWN
UP
)/PIN
AIB
!LTERNATEFUNCTIONOUTPUT
!LTERNATEFUNCTIONINPUT
PUSHPULLOR
OPENDRAIN
&ROMONCHIP
PERIPHERAL
4OONCHIP
PERIPHERAL
/UTPUT
CONTROL
6
$$
6
33
44,3CHMITT
TRIGGER
ON
)NPUTDRIVER
/UTPUTDRIVER
0-/3
.-/3
)N
PUT
DATA
REGI
ST
E
R
/UT
P
UT
D
ATA
REGIST
ER
2EADWRITE
2EAD
"
IT
SET
RESET
REGIST
ERS
7RITE
ONOFF
ONOFF
6
$$
6
33
6
33
6
$$
PROTECTION
DIODE
PROTECTION
DIODE
0ULL
0ULL
)/PIN
DOWN
UP
AIB