ST7LITEUS5 datasheet(60/136 Pages) STMICROELECTRONICS

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I/O ports

ST7LITEUS2, ST7LITEUS5

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Spurious interrupts

When enabling/disabling an external interrupt by setting/resetting the related OR register bit,

a spurious interrupt is generated if the pin level is low and its edge sensitivity includes

falling/rising edge. This is due to the edge detector input which is switched to '1' when the

external interrupt is disabled by the OR register.

To avoid this unwanted interrupt, a "safe" edge sensitivity (rising edge for enabling and

falling edge for disabling) has to be selected before changing the OR register bit and

configuring the appropriate sensitivity again.

Caution:

In case a pin level change occurs during these operations (asynchronous signal input), as

interrupts are generated according to the current sensitivity, it is advised to disable all

interrupts before and to reenable them after the complete previous sequence in order to

avoid an external interrupt occurring on the unwanted edge.

This corresponds to the following steps:

To enable an external interrupt:

Set the interrupt mask with the SIM instruction (in cases where a pin level change

could occur)

Select rising edge

Enable the external interrupt through the OR register

Select the desired sensitivity if different from rising edge

Reset the interrupt mask with the RIM instruction (in cases where a pin level

change could occur)

2. To disable an external interrupt:

Set the interrupt mask with the SIM instruction SIM (in cases where a pin level

change could occur)

Select falling edge

Disable the external interrupt through the OR register

Select rising edge

9.2.2

Output modes

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.

Table 17.

DR register value and output pin status(1)

When switching from input to output mode, the DR register has to be written first to drive the correct level

on the pin as soon as the port is configured as an output.

Push-pull

Open-drain

0VSS

VSS

1VDD

Floating

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