ST7263BEx datasheet(44/186 Pages) STMICROELECTRONICS

44 / 186 page

I/O ports

ST7263Bxx

44/186

Doc ID 7516 Rev 8

Output mode

The pin is configured in output mode by setting the corresponding DDR register bit (see

Table 7).

In this mode, writing “0” or “1” to the DR register applies this digital value to the I/O pin

through the latch. Therefore, the previously saved value is restored when the DR register is

read.

Note:

The interrupt function is disabled in this mode.

Digital 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 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 has to be configured in input

mode. In this case, the pin’s state is also digitally readable by addressing the DR register.

Note:

Input pull-up configuration can cause an unexpected value at the input of the alternate

peripheral input.

When the on-chip peripheral uses a pin as input and output, this pin must be configured as

an input (DDR = 0).

Caution:

The alternate function must not be activated as long as the pin is configured as an 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 a 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.

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