interfacing 3.3v and 5v logic circuits

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Can 3.3v microprocessor directly be interfaced with a 5v TTL circuit or how
to interface them?



Re: interfacing 3.3v and 5v logic circuits
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It depends. Some 3V3 microcontrollers have 5V tolerant inputs, and they
can be stuck on directly to HCT threshold logic, and HC logic but watch
the worst- case high threshold, as it's typically about 3V but is
specified at 3.5V max. For the rest, you'll need to read the data sheet
of the device you want to connect to.

Pure outputs aren't much of a problem, either into HC type logic or
FETs, watch the threshold again.

When, like the MSP430, the controller isn't 5V tolerant, there are
matching logic families like LVCH that can match a few inputs. If you
have a lot of IO to be matched, you may be as well off to interface via
something like a small Coolrunner which is 5V tolerant.

Or you can use resistor matching networks, or resistors and zeners,
which are cheaper in parts but might be more expensive in space and
construction costs.

Paul Burke

Re: interfacing 3.3v and 5v logic circuits
<sp> writes:
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Is the 3.3V microprocessor 5 volt tolerant ?

If not, have you considered using something like zener diodes ?

Which microprocessor is it anyway ?

Simon.

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Simon Clubley, clubley@remove_me.eisner.decus.org-Earth.UFP      
Microsoft: The Standard Oil Company of the 21st century

Re: interfacing 3.3v and 5v logic circuits
Pericom make some nice interfacing IC's - very quick on samples too...



"Susan Perkova" <sp> wrote in message
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Re: interfacing 3.3v and 5v logic circuits
Try a level translator from  dallas semicondutor or some other company.
You can plugin different voltages at different ports and the signals
work for your application without damaging your chips. For details go
to the website of  maxim-ic . Check the level translator which suits
your bandwidth / voltage requirements.

Regards,
Amit.


Re: interfacing 3.3v and 5v logic circuits

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If your micro isn't 5V tolerant, you must put something in your
circuit between processor and 5V powered circuit. Something LVC (powered
from 3V3 and are 5V tolerant) would do the job, e.g

http://www.standardics.philips.com/products/lvc /

Regards,

Paul.

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