L9805E datasheet(35/127 Pages) STMICROELECTRONICS

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L9805E

On-Chip Peripherals

35/127

In case of a floating input with interrupt configuration, special care must be taken when

changing the configuration (see Figure 17).

The external interrupts are hardware interrupts, which means that the request latch (not

accessible directly by the application) is automatically cleared when the corresponding

interrupt vector is fetched. To clear an unwanted pending interrupt by software, the

sensitivity bits in the Miscellaneous register must be modified.

Output Mode

The output configuration is selected by setting the corresponding DDR register bit. In this

case, writing the DR register applies this digital value to the I/O pin through the latch. Then

reading the DR register returns the previously stored value.

Two different output modes can be selected by software through the OR register: Output

push-pull and open-drain.

DR register value and output pin status:

Alternate function

When an on-chip peripheral is configured to use a pin, the alternate function is automatically

selected.

This alternate function takes priority over the standard I/O programming.

When the signal is coming from an on-chip peripheral, the I/O pin is automatically

configured in output 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 unexpected value at the input of the alternate

peripheral input. When an on-chip peripheral use a pin as input and output, this pin has to

be configured in input floating mode.

Push-Pull

Open-drain

Vss

VDD

Floating

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