Subject:
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Re: Help with cables
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Thu, 14 Jan 1999 14:24:49 GMT
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Original-From:
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fthompson9@aol.com^Spamless^
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Viewed:
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946 times
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milind,
To check your phone cord, hold the ends together so that the wires are
away from each other. Look through the clear connector. The wire colors
should line up in this orientation.
There is a little more to the DB-25 issue. "Null modem" vs. "straight
through" has two important differences. The one that is probably bothering
you has to do with the ordering of pins 2 and 3 (Tx and Rx). The "straight
through" cable does not swap the order of the wires. It is designed to go
between a computer and a modem. One transmits on pin 2 and the other receives
on pin 2. A "null modem" cable is designed to connect two "computer" type
devices who both transmit on pin 2 (or is it pin 3, no matter). This type of
cable swaps pins 2 and 3 at the connectors. Another important function of the
null modem cable is to be sure "data terminal ready" and "clear to send" are
held at appropriate levels. There are a couple of ways to do this. I make
them by having one conector (the computer end) with a jumper shorting pins 4
to 5 and another jumper shorting pins 6, 8, and 20. These "null modem" cables
became popular when the IBM PC came out. Before that most computer (micros
any way) didn't look at those pins and you only had to worry about pins 2 and
3. But the PC would not transmit unless CTS and DTR were set.
If you look on page 59 of the technical manual you will see that pins
5,6, and 20 are shorted together to take care of CTS and DTR. So I would
guess that your serial cable should pass lines 2,3,5,6,7, and 20. Be sure
that your cable has these and does not swap pins 2 and 3. If not pull out a
soldering iron. If 2 and 3 are swapped, swap them back. If 5,6 and 20 are not
passed through, jumper them on the computer end. I just checked my cables and
pin 2 on the computer end (female) does go to pin 2 on the Handy board end
(male). A paper clip will help get a meter probe into those female pin holes.
Hope this helps
Pherd
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