
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
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
Inpu
t dat
a regi
st
er
Out
pu
t dat
a regi
st
er
Read/write
Read
Bi
t s
e
t/
re
se
t regi
st
ers
Write
on/off
on/off
V
DD
V
SS
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