Output Configuration; Figure 16. Output Configuration - ST STM32F101 series Reference Manual

RM0008
9.1.8

Output configuration

When the I/O Port is programmed as Output:
•
The Output Buffer is enabled:
–
–
•
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 16 on page 164
Read
Write
Read/write
1. V is a potential specific to five-volt tolerant I/Os and different from V
DD_FT
General-purpose and alternate-function I/Os (GPIOs and AFIOs)
Open Drain Mode: A "0" in the Output register activates the N-MOS while a "1" in
the Output register leaves the port in Hi-Z. (the P-MOS is never activated)
Push-Pull Mode: A "0" in the Output register activates the N-MOS while a "1" in the
Output register activates the P-MOS.
shows the Output configuration of the I/O Port bit.

Figure 16. Output configuration

Input driver
Output driver
DocID13902 Rev 15
on
TTL Schmitt
trigger
V
DD
P-MOS
Output
control
N-MOS
V
SS
.
DD
V
or V
DD
Protection
diode
Protection
diode
V
SS
Push-pull or
Open-drain
(1)
DD_FT
I/O pin
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