ST STM32L4+ Series Reference Manual page 338

General-purpose I/Os (GPIO)
8.3.9 Input configuration
When the I/O port is programmed as input:
•
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
Figure 27
Read
Write
Read/write
8.3.10 Output configuration
When the I/O port is programmed as output:
• The output buffer is enabled:
–
–
•
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
Figure 28
338/2301
shows the input configuration of the I/O port bit.
Figure 27. Input floating/pull up/pull down configurations
input driver
output driver
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
shows the output configuration of the I/O port bit.
on
TTL Schmitt
trigger
RM0432 Rev 6
RM0432
V DDIOx
V DDIOx
on/off
protection
diode
pull
up
I/O pin
on/off
protection
pull
diode
down
V SS
V SS
MS31477V1