ST STM32F105 series User Manual

General-purpose and alternate-function I/Os (GPIOs and AFIOs) RM0008
165/1128 DocID13902 Rev 15
9.1.9 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 165 shows the Alternate Function Configuration of the I/O Port bit.
Also, refer to Section 9.4: AFIO registers on page 183 for further information.
A set of Alternate Function I/O registers allow you to remap some alternate functions to
different pins. Refer to Section 9.3: Alternate function I/O and debug configuration (AFIO).
Figure 17. Alternate function configuration
1. V
DD_FT
is a potential specific to five-volt tolerant I/Os and different from V
DD
.
Alternate Function Output
Alternate Function Input
push-pull or
open-drain
From on-chip
peripheral
To on-chip
peripheral
Output
control
I/O pin
V
DD
V
SS
TTL Schmitt
trigger
VSS
V
DD
or V
DD_FT
(1)
Protection
diode
Protection
diode
on
Input driver
Output driver
P-MOS
N-MOS
Input data register
Output data register
Read/write
Read
Bit set/reset registers
Write
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ST STM32F105 series Specifications

General

Brand	ST
Model	STM32F105 series
Category	Microcontrollers
Language	English