Alternate Function Configuration; Figure 16. Output Configuration; Figure 17. Alternate Function Configuration - ST STM32F205 series Reference Manual

RM0033
Read
Write
Read/write
6.3.11

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 17
To on-chip
peripheral
Read
Write
Read/write
From on-chip
peripheral

Figure 16. Output configuration

Input driver
Output driver
shows the Alternate function configuration of the I/O port bit.

Figure 17. Alternate function configuration

Alternate function input
Alternate function output
on
TTL Schmitt
trigger
Output
control
V
on
TTL Schmitt
trigger
Input driver
Output driver
Output
control
RM0033 Rev 8
General-purpose I/Os (GPIO)
V
DD
on/off
pull
up
V
DD
on/off
P-MOS
pull
down
V
SS
N-MOS
Push-pull or
SS
Open-drain
V
on/off
on/off
V
DD
P-MOS
V
N-MOS
push-pull or
V
SS
open-drain
V
DD
protection
diode
I/O pin
protection
diode
V
SS
ai15941b
V
DD
DD
protection
diode
Pull
up
I/O pin
protection
Pull
down
diode
V
SS
SS
ai15942b
147/1378
158