[Yaesu] Straight and Null Modem serial cable

Tue, 15 Oct 2002 19:41:10 -0400

Sometimes I find that there are sites on the net that do a great job of
explaining and provide graphics also.

http://www.loop-back.com/null-mod.html

http://www.vision.net.au/~timotsc/null/nullmodem.htm

http://www.nullmodem.com/NullModem.htm

I found these on the first page of a search on Google.

Randy

---
Randy Jarrett  WA4MEI      | MAIL:
EMAIL [email protected]        | 54 Patterson Road SW
PHONE (770)822-1096        | Lawrenceville, GA  30044-4620

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of [email protected]
Sent: Tuesday, October 15, 2002 8:43 AM
To: Edward B. Soriano, M.D.
Cc: [email protected]; [email protected]; [email protected]
Subject: Re: [Yaesu] Straight and Null Modem serial cable

A straight cable is where TX and RX pins are connected such that
TX (Pin x) on one end is connected to RX (Pin y) on the other..
Null modem wires the pins straight through...Pin x on one end
goes to pin x on the other and Pin y to Pin y..

The way to determine what you need is what kind of equipment you have.
A Modem is called a Data Comm Equipment or DCE...it accepts commands
from a Data Terminal Equipment or DTE....a straight cable connects
the DTE to a DCE....if you have two of the same (terminal or modem)
you need a null cable....this is all due to the standard of a RS232
connector (either DB25 or DB9 usually).
There are some extra pins involved that may cross DTR (Data Terminal
Ready) back to CTS (Clear to Send) and other control lines...
but usually they are not needed....a SIMPLE null cable merely connects
TX and RX to the same pins on the other end...a complicated Null Modem
cable wires crosses pins on one end to other signaling pins on the
other to allow the units to think they see the correct control signals.
USUALLY this can be gotten around by setting the device to ignore
these leads and only look for serial data...BUT some devices MUST see
these leads active before sending or receiving data!
If you have problems with a null modem cable, check to see if there
is a way to IGNORE hardware flow control or change it to software
(using CTRL x commands)...that usually gets around any hardware
issues.

Chris
WB5ITT

"Edward B. Soriano, M.D." wrote:
>
> Sorry for the ignorance. Can someone tell me the difference between a
"straight serial cable" and a "null modem" type of serial cable.
>
> Been trying to connect my FT847 to my notebook with no avail. No problem
with my FT 920. The manual says one must use the null modem type. Not sure
if I got the right one.
>
> Software is LOGIC 5.2
>
> Thanks!

Moderator: Ray Brown, KBXSTN
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