ST7FOXU0 datasheet(62/123 Pages) STMICROELECTRONICS

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I/O ports

ST7FOXU0

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9.2.4

Analog alternate function

Configure the I/O as floating input to use an ADC input. The analog multiplexer (controlled

by the ADC registers) switches the analog voltage present on the selected pin to the

common analog rail, connected to the ADC input.

Analog Recommendations

Do not change the voltage level or loading on any I/O while conversion is in progress. Do not

have clocking pins located close to a selected analog pin.

Caution:

The analog input voltage level must be within the limits stated in the absolute maximum

ratings.

9.3

I/O port implementation

The hardware implementation on each I/O port depends on the settings in the DDR and OR

registers and specific I/O port features such as ADC input or open drain.

Switching these I/O ports from one state to another should be done in a sequence that

prevents unwanted side effects. Recommended safe transitions are illustrated in Figure 28.

Other transitions are potentially risky and should be avoided, since they may present

unwanted side-effects such as spurious interrupt generation.

Figure 28.

Interrupt I/O port state transitions

9.4

Unused I/O pins

Unused I/O pins must be connected to fixed voltage levels. Refer to Section 12.8: I/O port

pin characteristics.

9.5

Low power modes

floating/pull-up

interrupt

INPUT

floating

(reset state)

INPUT

open-drain

OUTPUT

push-pull

OUTPUT

= DDR, OR

Table 18.

Effect of low power modes on I/O ports

Mode

Description

Wait

No effect on I/O ports. External interrupts cause the device to exit from Wait

mode.

Halt

No effect on I/O ports. External interrupts cause the device to exit from Halt

mode.

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