ST7LITE20F2 datasheet(65/166 Pages) STMICROELECTRONICS

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ST7LITE20F2 ST7LITE25F2 ST7LITE29F2

I/O ports

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10.2.3

Alternate functions

Many ST7s I/Os have one or more alternate functions. These may include output signals

from, or input signals to, on-chip peripherals. The Device Pin Description table describes

which peripheral signals can be input/output to which ports.

A signal coming from an on-chip peripheral can be output on an I/O. To do this, enable the

on-chip peripheral as an output (enable bit in the peripheral’s control register). The

peripheral configures the I/O as an output and takes priority over standard I/O programming.

The I/O’s state is readable by addressing the corresponding I/O data register.

Configuring an I/O as floating enables alternate function input. It is not recommended to

configure an I/O as pull-up as this will increase current consumption.

Before using an I/O as an alternate input, configure it without interrupt. Otherwise spurious

interrupts can occur.

Configure an I/O as input floating for an on-chip peripheral signal which can be input and

output.

Caution:

I/Os which can be configured as both an analog and digital alternate function need special

attention.

The user must control the peripherals so that the signals do not arrive at the same time on

the same pin. If an external clock is used, only the clock alternate function should be

employed on that I/O pin and not the other alternate function.

Figure 31. I/O port general block diagram

DDR

PAD

VDD

Alternate

enable

Alternate

output

OR SEL

DDR SEL

DR SEL

Pull-up

condition

P-buffer

(see table below)

N-buffer

PULL-UP

(see table below)

Analog

input

If implemented

Alternate

input

VDD

Diodes

(see table below)

From

other

bits

External

request (eix)

interrupt

Sensitivity

selection

CMOS

Schmitt

trigger

access

bit

From on-chip periphera

To on-chip peripheral

Combinational

Logic

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