ST6255CB1 datasheet(37/86 Pages) STMICROELECTRONICS

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ST62T55C ST62T65C/E65C

4 ON-CHIP PERIPHERALS

4.1 I/O PORTS

The MCU features Input/Output lines which may

be individually programmed as any of the following

input or output configurations:

– Input without pull-up or interrupt

– Input with pull-up and interrupt

– Input with pull-up, but without interrupt

– Analog input

– Push-pull output

– Open drain output

The lines are organised as bytewise Ports.

Each port is associated with 3 registers in Data

space. Each bit of these registers is associated

with a particular line (for instance, bits 0 of Port A

Data, Direction and Option registers are associat-

ed with the PA0 line of Port A).

The DATA registers (DRx), are used to read the

voltage level values of the lines which have been

configured as inputs, or to write the logic value of

the signal to be output on the lines configured as

outputs. The port data registers can be read to get

the effective logic levels of the pins, but they can

be also written by user software, in conjunction

with the related option registers, to select the dif-

ferent input mode options.

Single-bit operations on I/O registers are possible

but care is necessary because reading in input

mode is done from I/O pins while writing will direct-

ly affect the Port data register causing an unde-

sired change of the input configuration.

The Data Direction registers (DDRx) allow the

data direction (input or output) of each pin to be

set.

The Option registers (ORx) are used to select the

different port options available both in input and in

output mode.

All I/O registers can be read or written to just as

any other RAM location in Data space, so no extra

RAM cells are needed for port data storage and

manipulation. During MCU initialization, all I/O reg-

isters are cleared and the input mode with pull-ups

and no interrupt generation is selected for all the

pins, thus avoiding pin conflicts.

Figure 22. I/O Port Block Diagram

VDD

RESET

SIN CONTROLS

SOUT

SHIFT

REGIST ER

DATA

DIRECTION

REGISTE R

OPTION

REGISTE R

INPUT /OUTPUT

TO INTERRU PT

VDD

TO ADC

VA00413

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