ST63142 datasheet(28/86 Pages) STMICROELECTRONICS

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INPUT/OUTPUT PORTS

The ST631xx 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)

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 (PA0-PA7)

- Open-drain output 5V (PB5-PB7, PC3, PC5-

PC7)

- Push-pull output (PB0-PB4, PC0-PC2, PC4)

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

The ports occupy 6 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

configured in the output mode. The port Data Reg-

isters can be read to get the effective logic levels of

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

software, in conjunction with the related Data Di-

rection Register, to select the different input mode

options. Single-bit operations on I/O registers (bit

set/reset instructions) are possible but care is nec-

essary 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 configuration. 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. 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 which is set in output mode and

is set low).

Details of I/O Ports

When programmed as an input a pull-up resistor (if

available) can be switched active under program

control. When programmed as an output the I/O

port will operate either in the push-pull mode or the

open-drain mode according to the hardware fixed

configuration as specified below.

Port A. PA0-PA7 are available as an open-drain

only (no push-pull programmability and no resis-

tive pull-up in input mode) capable of withstanding

12V while the normal open drain has standard rat-

ings of VDD + 0.3V. This I/O port has been specially

designed for direct LED driving and is able to sink

up to 30mA with a maximum VOL of 1V.

Some Port B and C lines are also used as I/O buff-

ers for signals coming from the on-chip SPI and

OSD.

In this case the final signal on the output pin is

equivalent to a wired AND with the programmed

data output.

If the user needs to use the SPI or the OSD, then

the I/O line should be set in output mode while the

open-drain configuration is fixed in hardware ; the

corresponding data bit must be set to one.

PB2 and PB3 must be programmed in input mode

to provide the HSYNC and VSYNC input signals to

the OSD.

On ST631xx the I/O pins with double or special

functions are:

- PB2/VSYNC (connected to the OSD VSYNC

signal)

- PB3/HSYNC (connected to the OSD HSYNC

signal)

- PB5/SCL (connected to the SPI clock signal)

- PB6/SDA (connected to the SPI data signal)

- PB7/SEN (connected to the SPI enable signal)

- PC2-ON-OFF, this I/O is specially suited to TV

SET ON-OFF and for this reason at reset the

related Data Direction bit will be automatically

set to one (I/O line is in output mode), while the

rest of the port is in input mode

- PC3/BLANK (connected to the OSD Blank sig-

nal)

- PC5/R, PC6/G, PC7/B (connected to the OSD

R-G-B signals)

All the Port A,B and C I/O lines have Schmitt-trig-

ger input configuration with a typical hysteresis of

1V.

ST63140,142,126,156

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