can an AVR generate a RS-232 signal with a VCC of 5V?

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Hi - I would like to interface a AVR with a 9 pin com port on a computer.
Can an AVR generate valid RS-232 signals with a vcc of 5V? Or do I need one
of those Maxim serial level converter chips? Thanks!

Re: can an AVR generate a RS-232 signal with a VCC of 5V?
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computer.
one

There's 3rd party clones of the MAX232 that do equally well. I frequently
use the ST232, which is available from most distributors.

Rob



Re: can an AVR generate a RS-232 signal with a VCC of 5V?

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Me, too. It's under 1 Euro (Dollar) in single quantities and only
needs 100nF capacitors (like the MAX232A ;-)

 Jan-Hinnerk


Re: can an AVR generate a RS-232 signal with a VCC of 5V?

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one

If you use a software UART you can get the correct polarity signals. They
only swing from 0V to +5V, but that is acceptable to most PCs. I tried this
once, and it worked OK.

Leon
--
Leon Heller, G1HSM
leon snipped-for-privacy@hotmail.com
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Re: can an AVR generate a RS-232 signal with a VCC of 5V?
Also if you're really cheap you can use a not gate on the hardware uart.
Don't forget to put a resistor + 5V zener on the RX side.

It works ok in some situations.

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computer.
this



Re: can an AVR generate a RS-232 signal with a VCC of 5V?

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Cheap?? For extra cheapness, leave out the zener. The RX gate input
protection diodes will swing into action and take it's place.

In fact, that series resistor looks a bit extravagent too.... RS232 is
current limited already, after all :)

--

John Devereux

Re: can an AVR generate a RS-232 signal with a VCC of 5V?
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And I've tried it a dozen times: it works
Wade Hassler

Re: can an AVR generate a RS-232 signal with a VCC of 5V?


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Most of RS232 drivers can accept TTL levels, but not all of them.

I used to think that it always works, until I encountered the PC from
Dell (can't remember the particular model). That was the first occasion.

I was burned the second time with the RS232 drivers from SIPEX. Those
drivers are switching to sleep mode if the input voltage is inside
+/-3V. So, if you drive them from TTL, they tend to sleep down and that
may cause different problems.

Vladimir Vassilevsky, Ph.D.

DSP and Mixed Signal Design Consultant

http://www.abvolt.com

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