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11 messages in this thread
Hello y'all! I've got a big problem… You see, I have an IBM PC XT with some
Amiga files in it. How can I transfer these files to my Amiga? I was thinking
that a NULL modem will solve my problem, but I'm not sure what a NULL modem is.
Could it be a RS-232 serial cable connected to both computers? I was planning
to use communication programs to transfer these files without using a telephone
line. Any help would be gladly appreciated.
Thanks, David Bann (76566,3610)
David,
Yes, a NULL MODEM cable is a cable that swaps a few of the wires so that each
side thinks it's talking to something like a modem. You can usually get by with
three wires… pin 7 goes straight through. Pin 2 connects to pin 3, and pin 3
connects to pin 2. If you need more than this, as you might if your IBM thing
requires more of the RS232 signals, let us know. You can also buy NULL MODEM
adapters at most any clone store for about $10 or less.
-larry
Or an easier way would be to connect a modem to both computers and use a phone
wire to connect the two modems and there you go.
Marc!
Marc,
Absolutely not….
First, phone wires don't "just hook", although for short distances this
_might_ work.
However, if you've only a short distance to go….why waste 2 modems?
You forget what a modem is..it's a MODulator/DEModulator. It takes a
digital signal, modulates it on an audio carrier so it can be sent over phone
lines as "normal audio". It also receives that modulated carrier and
demodulates it back into a digital signal that your computer can understand.
With a NULL modem, you simply don't bother to modulate the signal, thus
don't need to demodulate it on the other end…thus no need for modems at both
ends. NULL modems only work over short distances (RS232 lengths… about 250
feet max) because the signal is subject to line effects at longer distances
(which is why we have modems in the first place, to eliminate those line
effects over long distances).
A NULL modem is simply a cable that flips lines 2 and 3 between the 2
computers and also normally cross connects lines 6 8 and 20 one each end. You
can buy them at Radio Shack for about $15.
Don
Fine fine, buy a NULL Modem. BTW, I knew what a NULL Modem was and what a Modem
was. I just thought maybe you'd have two modems hanging around.. 🙂
Marc!
Marc,
I'm not the one who needed to transfer the files, but even if I was,
the method you described is expensive…and unreliable at best.
Normal phone lines (not just plugging an extension cord between 2
modems) are amplified so modems work fine with them, wires strung between 2
modems aren't amplified, so they just don't cut it very well.
I have tried your method in the past…anything longer than about 6
feet on the phone cable and it just had too many errors.
Don
Okay, so I was wrong Ron. Thanks for telling me. Now I'll never try it!
Marc!
don,
don't forget looping 4 back to 5 if you need RTS and driving 7 straight
through though over most null modem distances ground isn't too big a hassel if
it does come into play it's a real pain to debug
lg
Larry,
You're right…I always forget about them since nothing I use does
anything with RTS/CTS.
Don
David,
If you have a 3 1/2" disk on your XT, or if you have a 5 1/4" drive for your
Amiga, you can do it with PCUtils. Otherwise, the null modem cable might be
the best. A null modem cable is not the same as an RS-232 cable – not as many
wires attached. I made one once, but all I recall at the moment is that pins 2
and 3 were attached to opposite wires at the two ends of the cable. I know
there were jumpers on several of the pins – but I'll bet someone here can tell
you EXACTLY how to make one! It isn't hard – it was my first ever soldering
project, and it was easy to do.
Betty
Thanks for the tip, Betty. Just yesterday I've acquired the NULL modem cable
and it works fine.
David (76566,3610)