ST72321R7-Auto datasheet(74/243 Pages) STMICROELECTRONICS

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I/O ports

ST72321xx-Auto

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Doc ID 13829 Rev 1

Caution:

The alternate function must not be activated 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 selected pin to the common analog rail which is connected 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 analog pin.

Warning:

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 feature of the I/O port such as ADC Input or true 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 30.

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

unwanted side-effects such as spurious interrupt generation.

Figure 30.

Interrupt I/O port state transitions

The I/O port register configurations are summarized in the following table.

Table 31.

I/O port configuration

Port

Pin name

Input (DDR = 0)

Output (DDR = 1)

OR = 0

OR = 1

OR = 0

OR = 1

Port A

PA7:6

floating

true open-drain

PA5:4

floating

pull-up

open-drain

push-pull

PA3

floating

floating interrupt

open-drain

push-pull

PA2:0

floating

pull-up interrupt

open-drain

push-pull

floating/pull-up

interrupt

INPUT

floating

(reset state)

INPUT

open-drain

OUTPUT

push-pull

OUTPUT

= DDR, OR

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