ST6380 datasheet(28/82 Pages) STMICROELECTRONICS

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ST6380, ST6381, ST6382, ST6383, ST6388, ST6389

4 ON-CHIP PERIPHERALS

4.1 I/O PORTS

The ST638x microcontrollers use three standard I/

O ports (A,B,C) with up to eight pins on each port;

refer to the device pin configurations to see which

pins are available.

Each line can be individually programmed either in

the input mode or the output mode as follows by

software.

– Output

– Input with on-chip pull-up resistor (selected by

software)

– Input without on-chip pull-up resistor (selected

by software)

– Analog inputs (PB0-PB6)

Note: pins with 12V open-drain capability do not

have pull-up resistors.

In output mode the following hardware configura-

tions are available:

– Open-drain output 12V (PA4-PA7, PC4-PC7)

– Open-drain output 5V (PC0-PC3, PB0-PB6)

– Push-pull output (PA0-PA3, PB0-PB6)

The lines are organized in three ports (port A,B,C).

The ports occupy 7 registers in the data space.

Each bit of these registers is associated with a par-

ticular line (for instance, the bits 0 of the Port A Data

and Direction registers are associated with the PA0

line of Port A).

There are three Data registers (DRA, DRB, DRC),

that are used to read the voltage level values of the

lines programmed in the input mode, or to write the

logic value of the signal to be output on the lines con-

figured in the output mode. The port Data Registers

can be read to get the effective logic levels of the

pins, but they can be also written by the user soft-

ware, in conjunction with the related Data Direction

select the different input mode options. Single-bit

operations on I/O registers (bit set/reset instruc-

tions) are possible but care is necessary because

reading in input mode is made from I/O pins and

therefore might be influenced by the external load,

while writing will directly affect the Port data register

causing an undesired changes of the input config-

uration. The three Data Direction registers (DDRA,

DDRB, DDRC) allow the selection of the direction

of each pin (input or output).

All the I/O registers can be read or written as any

other RAM location of the data space, so no extra

RAM cell is needed for port data storing and ma-

nipulation. During the initialization of the MCU, all

the I/O registers are cleared and the input mode with

pull-up is selected on all the pins thus avoiding pin

conflicts (with the exception of PC2 that is set in out-

put mode and is set high i.e. high impedance).

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