Alternate Function Configuration; Figure 21. Output Configuration; Figure 22. Alternate Function Configuration - ST STM32F40 Series Reference Manual

General-purpose I/Os (GPIO)

Figure 21. Output configuration

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 22

Figure 22. Alternate function configuration

To on-chip
peripheral
Read
Write
Read/write
From on-chip
peripheral
195/1422
Input driver
Output driver
shows the Alternate function configuration of the I/O port bit.
Alternate function input
Alternate function output
Doc ID 018909 Rev 4
on
TTL Schmitt
trigger
V
DD
P-MOS
Output
control
N-MOS
V
SS
on
TTL Schmitt
trigger
Input driver
Output driver V
Output
control
V
SS
V
V
DD
on/off
pull
up
on/off
pull
down
V
SS
V
Push-pull or
Open-drain
V
DD
on/off
Pull
up
on/off
DD
Pull
P-MOS
down
V
SS
N-MOS
push-pull or
open-drain
RM0090
DD
protection
diode
I/O pin
protection
diode
SS
ai15941b
V
DD
protection
diode
I/O pin
protection
diode
V
SS
ai15942b