RM0090: Reference manual - STMicroelectronics

General-purpose I/Os (GPIO) RM0090
Figure 21. Output configuration
Write
Read
Read/write
Bit set/reset registers
Input driver
Output driver
7.3.11 Alternate function configuration
Output data register
TTL Schmitt
trigger
Output
control
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 shows the Alternate function configuration of the I/O port bit.
Figure 22. Alternate function configuration
To on-chip
peripheral
Write
Read
Bit set/reset registers
Read/write
From on-chip
peripheral
195/1416 Doc ID 018909 Rev 3
Input data register
Alternate function input
Output data register
Input data register
Alternate function output
Input driver
Output driver
on
on
TTL Schmitt
trigger
Output
control
V DD
P-MOS
N-MOS
Push-pull or
VSS Open-drain
V DD
P-MOS
N-MOS
V
push-pull or
SS open-drain
on/off
on/off
V DD
pull
up
V DD
protection
diode
pull protection
down diode
VSS VSS on/off
on/off
V DD
Pull
up
Pull
down
V DD
V SS VSS
I/O pin
ai15941b
protection
diode
I/O pin
protection
diode
ai15942b