STM32F101xx, STM32F102xx, STM32F103xx, STM32F105xx and ...

RM0008
General-purpose and alternate-function I/Os (GPIOs and AFIOs)
Figure 16.
Output configuration
Read
Write
Bit set/reset registers
Read/write
Output data register
Input data register
Input driver
Output driver
on
TTL Schmitt
trigger
Output
control
V DD
P-MOS
N-MOS
Push-pull or
V SS Open-drain
V DD or V DD_FT (1)
V SS
Protection
diode
Protection
diode
I/O pin
ai14784
1. V DD_FT is a potential specific to five-volt tolerant I/Os and different from V DD .
8.1.9 Alternate function configuration
When the I/O Port is programmed as Alternate Function:
●
The Output Buffer is turned on in Open Drain or Push-Pull configuration
● The Output Buffer is driven by the signal coming from the peripheral (alternate function
out)
● The Schmitt Trigger Input is activated
● The weak pull-up and pull-down resistors are disabled.
● The data present on the I/O pin is sampled into the Input Data Register every APB2
clock cycle
● A read access to the Input Data Register gets the I/O state in open drain mode
● A read access to the Output Data register gets the last written value in Push-Pull mode
The Figure 17 on page 144 shows the Alternate Function Configuration of the I/O Port bit.
Also, refer to Section 8.4: AFIO registers on page 158 for further information.
A set of Alternate Function I/O registers allow you to remap some alternate functions to
different pins. Refer to
Doc ID 13902 Rev 9 143/995