ST72141K2 datasheet(34/132 Pages) STMICROELECTRONICS

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ST72141K

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I/O PORTS (Cont’d)

CAUTION: The alternate function must not be ac-

tivated as long as the pin is configured as input

with interrupt, in order to avoid generating spurious

interrupts.

Analog alternate function

When the pin is used as an ADC input, the I/O

must be configured as floating input. The analog

multiplexer (controlled by the ADC registers)

switches the analog voltage present on the select-

ed pin to the common analog rail which is connect-

ed to the ADC input.

It is recommended not to change the voltage level

or loading on any port pin while conversion is in

progress. Furthermore it is recommended not to

have clocking pins located close to a selected an-

alog pin.

WARNING: The analog input voltage level must

be within the limits stated in the absolute maxi-

mum ratings.

6.3 I/O PORT IMPLEMENTATION

The hardware implementation on each I/O port de-

pends on the settings in the DDR and OR registers

and specific feature of the I/O port such as ADC In-

put or true open drain.

Switching these I/O ports from one state to anoth-

er should be done in a sequence that prevents un-

wanted side effects. Recommended safe transi-

tions are illustrated in Figure 24 Other transitions

are potentially risky and should be avoided, since

they are likely to present unwanted side-effects

such as spurious interrupt generation.

Figure 24. Interrupt I/O Port State Transitions

The I/O port register configurations are summa-

rized as follows.

floating/pull-up

interrupt

INPUT

floating

(reset state)

INPUT

open-drain

OUTPUT

push-pull

OUTPUT

= DDR, OR

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