AVR-Chat

Not so much with RS232 but a lot in the old days with the printer ports and
dongles. We used to program security dongles from Vault and they would only
program with some printer port cards and not others. Once again the levels
differ by brands. If you Dell has a USB port you may be able to use one of
those USB to RS232 adapters.

Al

-----Original Message-----
From: Bruce Parham [mailto:obparham@jpl.nasa.gov]
Sent: Thursday, January 22, 2004 10:42 AM
To: AVR-Chat@yahoogroups.com
Subject: Re: [AVR-Chat] RS-232 Levels???


Mike Harrison wrote:
>
> You can get away with 5V for RS232, so if your levels ate -5.8 and +6 I
would be highly surprised if
> this was the problem, unless your driver IC has delay or risetime issues
at lower supply voltages.
> Are the RS232 chips you are using actually designed for 3.3v operation ?


samperi@ampertronics.com.au wrote:
>
> Is the RS232 (Max 232??) interface chip designed for 3.3V or 5V operation?
> It may have stopped working!!
>
> Regards
>
> John Samperi

Al Welch wrote:
>
> Look at the MAX3228 instead of the MAX232 for lower supply.
>
> According to Maxim...
>
> The MAX3228/MAX3229 are +2.5V to +5.5V powered EIA/TIA-232 and V.28/V.24
.
.
.
> Al Welch


The drivers don't seem to be the problem . The STK501 uses a MAX3232 rated
at 3.0-5.5v
to drive the 9-pin J301 connector. My board uses a pair of MAX3244's also
rated for
3.0-5.5v. The problem looks like the Dell PCs' +6v threshold.

I guess my real question, for the embedded types on the list, is has anyone
else run into
this issue talking to other brands of PC's or is this just a Dell box thing?

As an aside, I noticed that the AVR-JTAG pod didn't seem to have any trouble
talking to
my PC even when powered by the system 3.3v, so I opened it up. Low and
behold - a boost
supply shoving 7.3v into a 3-pin 5v linear regulator and a good ol' MAX202
5v only part.
So simple...

Bruce



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