ST7265X datasheet(50/166 Pages) STMICROELECTRONICS

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ST7265x

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I/O PORTS (Cont’d)

9.2.3 Alternate Functions

When an on-chip peripheral is configured to use a

pin, the alternate function is automatically select-

ed. This alternate function takes priority over the

standard I/O programming.

When the signal is coming from an on-chip periph-

eral, the I/O pin is automatically configured in out-

put mode (push-pull or open drain according to the

peripheral).

When the signal is going to an on-chip peripheral,

the I/O pin must be configured in input mode. In

this case, the pin state is also digitally readable by

addressing the DR register.

Note: Input pull-up configuration can cause unex-

pected value at the input of the alternate peripheral

input. When an on-chip peripheral use a pin as in-

put and output, this pin has to be configured in in-

put floating mode.

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.

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