Re: -5v and -12v Serial Ports

On Jun 1, 7:38 pm, "Bart" <bborb@fusedotnet> wrote:
Hi All,
A buddy of mine got a new computer, replacing his old 486. He uses
his
computer's serial port to "talk" to older equipment and now he's
having
problems. His new computer has a PCI card with a serial port and I
told him
it may be that the PCI (who's bus doesn't support -12volts) has
less of a
voltage peak to clearly send the data like his old 486 machine. His
cables
are kinda long and I figure he was pushing it even with his old
computer and
now that his serial is only +/-5v he can't quite get the data
across.
Is there a clear line in history of computers when this change
from -12v
to -5v was crossed in serial ports on PC's? I told him that any
computer
with ISA slots, even if the serial port was on the motherboard
would support
the -12v serial port he needs.
Am I way off base?
Thanks for any input,
Bart

I believe the original spec for RS-232 levels was minimum +/- 3v.
Calling Jim Thompson for enlightenment. I'm surprised about the +/- 5
thing. I thought most everybody used a MAX232 (or knock off) to make
+/- 10 from the 5 volt supply.

ISA slot? Where would you find one of those? I needed an ISA slot for
an EPROM programmer 4 or 5 years ago and the best I could do was a
late 90's Biostar board on eBay for $35. I also keep a Pentium 166
machine and a K6-2 550 'just in case'

GG

.

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