ST7LITE20F2 datasheet(67/166 Pages) STMICROELECTRONICS

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ST7LITE20F2 ST7LITE25F2 ST7LITE29F2

I/O ports

Doc ID 8349 Rev 5

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Analog alternate function

Configure the I/O as floating input to use an ADC input. The analog multiplexer (controlled

by the ADC registers) switches the analog voltage present on the selected pin to the

common analog rail, connected to the ADC input.

Analog recommendations

Do not change the voltage level or loading on any I/O while conversion is in progress. Do not

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.

10.3

I/O port implementation

The hardware implementation on each I/O port depends on the settings in the DDR and OR

registers and specific I/O port features such as ADC input or 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 32.

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

unwanted side-effects such as spurious interrupt generation.

Open-drain

output(2)

Push-pull

output(3)

When the I/O port is in input configuration and the associated alternate function is enabled as an output,

reading the DR register will read the alternate function output status.

When the I/O port is in output configuration and the associated alternate function is enabled as an input,

the alternate function reads the pin status given by the DR register content.

For true open drain, these elements are not implemented.

Table 23.

I/O configurations (continued)

I/O port

Hardware configuration

NOTE 3

PAD

RPU

Databus

DR register access

R/W

VDD

PAD

RPU

Databus

DR register access

R/W

VDD

Alternate

Enable

output

bit

From on-chip periphera

NOTE 3

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