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On 6 Aug 00, at 16:18, Kevin Schmidt wrote:
>
> I don't really understand this, but I believe (perhaps incorrectly)
> that laptops generally use charge pumps powered by the low voltage
> supply to generate the plus and minus 12 volts for the RS-232 signals.
> Therefore they often have a maximum current that can be drawn or sinked
> from all the pins, that is it is not current per pin but total current
> that matters. If hooking things up differently or enabling the port
That's very interesting; maybe it explains something that caused me to lose
many hours earlier this year.
I have one of the truly wonderful PIEXX boards, and I needed to upgrade the
firmware from the first beta to the production version. This is done via a
Windows program that communicates with the board via the COM port.
The easiest thing for me to do was to take a laptop to the rig rather than
take the rig to my desktop, but blowed if I could get the program to
communicate properly with the rig. This was with a Dell laptop that was
about a year old at the time.
Well, I thought it might just be something weird with the Dell (although
the serial port seemed to work fine when talking to other devices), so I
tried the same thing with my Compaq laptop that was about two years old at
the time. Same thing. So, having had two completely different laptops fail,
I figured it was a problem with the PIEXX board.
After mucking around for many hours here and chez N2IC, and wasting quite a
bit of Chris' ("Mr. PIEXX") time, we discovered that N2IC's desktop machine
didn't seem to have any problem talking to the board. When I brought the
rig home, I discovered that the same was true of my desktop. So the score
was: of two desktops tried, both could communicate fine with the board; of
two laptops tried, neither of them could do so.
So I concluded that there is something strange about the design of laptops
that is not generally known, and which the COM drivers don't flag, and yet
causes them to fail to behave properly under certain circumstances. I think
that what you have said goes a long way to explaining what this something
is.
Sure would be nice if the drivers flagged this problem when it might be
occurring, or if the so-called "Serial Port Troubleshooter" thingy in
Windows talked about it. But I suppose that would be too easy.
Back to TR discussions....
Doc N7DR
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D.R. Evans N7DR / G4AMJ N7DR@arrl.net
"Shadow" has been published (but don't blame me for the cover):
http://www.sff.net/people/N7DR/drevans.htp
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