General-purpose and alternate-function I/Os (GPIOs and AFIOs) RM0008
158/1096 Doc ID 13902 Rev 12
9.1.7 Input configuration
When the I/O Port is programmed as Input:
● The Output Buffer is disabled
● The Schmitt Trigger Input is activated
● The weak pull-up and pull-down resistors are activated or not depending on input
configuration (pull-up, pull-down or floating):
● 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 obtains the I/O State.
The Figure 15 on page 158 shows the Input Configuration of the I/O Port bit.
Figure 15. Input floating/pull up/pull down configurations
1. V
DD_FT
is a potential specific to five-volt tolerant I/Os and different from V
DD
.
9.1.8 Output configuration
When the I/O Port is programmed as Output:
● The Output Buffer is enabled:
– 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.
● 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
I/O pin
TTL Schmitt
trigger
V
SS
V
DD
or V
DD_FT
(1)
protection
diode
protection
diode
on
input driver
output driver
Input data register
Output data register
Read/write
Read
Bit set/reset registers
Write
on/off
on/off
V
DD
V
SS
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