RM0312 datasheet(77/275 Pages) STMICROELECTRONICS

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RM0312

General purpose I/O ports (GPIO)

Warning:

On some packages, some ports must be considered as active

even if they do not exist on the package. To avoid spurious

effects, configure them as pull-up inputs without interrupt at

startup, and keep them in this state when changing the port

configuration. Refer to the datasheet for additional

information.

10.3.1

Input modes

Clearing the DDRx bit selects input mode. In this mode, reading a IDR bit returns the digital

value of the corresponding I/O pin.

Refer to Section 10.7: Input mode details on page 79 for information on analog input,

external interrupts and Schmitt trigger enable/disable.

As shown in , four different input modes can be theoretically be configured by software:

floating without interrupt, floating with interrupt, pull-up without interrupt or pull-up with

interrupt. However in practice, not all ports have external interrupt capability or pull-ups. You

should refer to the datasheet pin-out description for details on the actual hardware capability

of each port.

Table 19. I/O port configuration summary

Mode

DDR

bit

CR1

bit

CR2

bit

Function

Pull-up

P-buffer

Diodes

to VDD

to VSS

Input

Floating without

interrupt

Off

Pull-up without

interrupt

Floating with interrupt

Off

Pull-up with interrupt

Output

Open drain output

Off

Push-pull output

Open drain output, fast

mode

Off

Push-pull, fast mode

Off

True open drain (on

specific pins)

Not implemented

Not im-

plemented

(1)

1. The diode connected to VDD is not implemented in true open drain pads. A local protection between the

pad and VOL is implemented to protect the device against positive stress.

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