
General-purpose I/Os (GPIO)
RM0453
398/1454
RM0453 Rev 2
10.3.9 Input
configuration
When the I/O port is programmed as input, the following occurs:
•
The output buffer is disabled.
•
The Schmitt trigger input is activated.
•
The pull-up and pull-down resistors are activated depending on the value in the
GPIOx_PUPDR register.
•
The data present on the I/O pin are sampled into the input data register every AHB
clock cycle.
•
A read access to the input data register provides the I/O state.
The figure below shows the input configuration of the I/O port bit.
Figure 45. Input floating/pull-up/pull-down configurations
10.3.10 Output
configuration
When the I/O port is programmed as output, the following occurs:
•
The output buffer is enabled:
–
Open drain mode: A 0 in the Output register activates the N-MOS whereas 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 whereas a 1 in the
Output register activates the P-MOS.
•
The Schmitt trigger input is activated.
•
The pull-up and pull-down resistors are activated depending on the value in the
GPIOx_PUPDR register.
•
The data present on the I/O pin are sampled into the input data register every AHB
clock cycle.
•
A read access to the input data register gets the I/O state.
•
A read access to the output data register gets the last written value.
on/off
pull
pull
on/off
I/O pin
VDDIOx
VSS
TTL Schmitt
trigger
VSS
VDDIOx
protection
diode
protection
diode
on
input driver
output driver
down
up
Inpu
t da
ta
regis
ter
Ou
tpu
t da
ta
regis
ter
Read/write
Read
Bi
t set/rese
t regis
ter
s
Write
MS31477V1