Digilent MX4cK Manuel d'utilisateur télécharger pdf (Page 12)

Cerebot MX4cK Reference Manual

www.digilentinc.com page 12 of 35

Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners.

Cerebot MX4cK to operate with 5V logic

devices.

There are two issues to consider when dealing

with 5V compatibility for 3.3V logic. The first is

protection of 3.3V inputs from damage caused

by 5V signals. The second is whether the 3.3V

output is high enough to be recognized as a

logic high value by a 5V input.

The digital I/O pins on the PIC32

microcontroller are 5V tolerant. It is safe to

apply 5V logic signals directly to these pins

without risk of damage to the microcontroller.

The analog capable I/O pins on the PIC32 are

not 5V tolerant. The absolute maximum

voltage rating for the analog pins is 3.6V.

Generally, the analog pins are the pins on I/O

port B, however, there are other non-5V

tolerant pins on the device.

Refer to the PIC32MX3XX/4XX Family Data

Sheet for more information about which pins

on the device are 5V tolerant before applying

input signals higher than 3.3V to any pin on the

Cerebot MX4cK board.

If a 5V signal is applied to a non-5V tolerant

pin, some external means must be used to limit

the applied voltage to 3.6V or less. The

Cerebot MX4cK board provides 200 ohm

series resistors between the microcontroller

pins and the Pmod connector pins. These

resistors are primarily intended to provide short

circuit protection on the outputs, but will also

provide limited protection if a 5V signal is

inadvertently applied to a non-5V tolerant pin.

One technique that can be used to limit and

input voltage to a safe level is to use a 200

ohm series resistor and Shotkey diode

connected to the 3.3V supply to clamp the

voltage.

The minimum output high voltage of the PIC32

microcontroller is rated at 2.4V when sourcing

12mA of current. When driving a high

impedance input (typical of CMOS logic) the

output high voltage will be close to 3.3V. Some

5V devices will recognize this voltage as a

logic high input, and some won’t. Many 5V

logic inputs will work reliably with 3.3V inputs.

If the 3.3V logic output is not sufficient for 5V

logic input to be reliably seen as a logic high

input signal, some external means must be

used to raise the output level. In some cases, a

pull-up resistor to 5V is sufficient. A pull-up

resistor in the range of 2Kohm–10kOhm can

be used. This technique should not be used

with pins that are not 5V tolerant on the PIC32

microcontroller.

1 2 ... 7 8 9 10 11 12 13 14 15 16 17 ... 34 35

Commentaires sur ces manuels

Pas de commentaire