Phoenix CD 2.0/Phoenix_CD.cdr/01e/modemuse.zip/MODEMUSE.TXT

Text File | 1988-05-04 | 10KB | 212 lines

                             Tips on Modem Use
                            by Michael A. Banks

                   Copyright (C), 1987, Michael A. Banks

     Modems aren't particularly difficult to set up and use.  On the other
hand, it's relatively easy to foul up your modem's operation through
carelessness or lack of knowledge.

       This article will serve as a guide in setting up and using your
modem.  If you observe the procedures and precautions mentioned herein,
you'll save yourself a lot of trouble later on.

                            Marking Connections
                                By the Book

     As with any electronic device, it is important that you connect your
modem properly and use it under practical operating conditions.  Study the
manual that comes with your modem to assure proper connection, and consult
with your computer store and the modem manufacturer's customer support
department if necessary.

                           Connectors and Cables

     The cables (and the connectors used with those cables) that connect a
computer's serial port with a modem are obviously very important elements
in the data transfer chain.  like serial ports, connectors and cables used
with serial ports must conform to the RS-232C standard.

     Connectors.  There are two types of RS-232 connectors--nine- and 25-
pin--and these may be male or female.  Nine- and 25-pin connectors are
known as DB9 and DB25 connectors, respectively.  Each type has numbered
pins (very important if you intend to make your own cables--saves a lot of
messing around with a continuity tester).

     DB connectors can be found on the serial port of your computer and
modem, and at either end of the connecting cable.  (A connecting cable is
typically a "ribbon cable"--a flat cable with multiple connectors.)

     Mixing Connectors.  DB-25 and DB-9 connectors can be used at opposite
ends of a cable if necessary (as when a computer's serial port has a DB-9
connector and its modem has a DB-25 connector).  All that's required for
the connection to be successful is that the pins on each connector be
properly wired (i.e., the wire on each numbered pin on the DB-9 connector
should be connected to the correspondingly-numbered pin on the DB-25
connector).

     Connector and Cable "Gender."  Incidentally, there's a standard that
dictates that the female version of a DB connector should be used only on
modems, while the male version should be used on computer serial ports.
Thus, a "standard" RS-232C cable will have a male connector on one end (to
connect with the modem), and a female connector on the other end (to
connect with the computer).

     Unfortunately, not all manufacturers follow this standard regarding
Using a Modem                                               Mike Banks - 2


the gender of their serial ports.  So, with some equipment you may find
that you have what is called a "gender problem."  (No sex-change jokes,
please--this is serious stuff!) when this is the case, you'll have to buy
or make an appropriate cable with both female or both male connectors.  Or,
you can obtain what are called "gender changes" to change the "sex" of one
end of the cable.

                         Telephone Plug/Jack Types

     Before plugging a telephone line's modular plug into a modem, make
sure of the plug's type.  Most modems are designed with modular jacks, but
modular (also designated "RJ") jacks and plugs come in more than one
variety.  Some are cross-compatible, and some aren't.

     Generally, a home or single-line business telephone system uses RJ-11
plugs, and these present no problem--even if the plugs are set up to
provide dial light power to a "Trimline" phone or other lighted dial
telephone set.  (The only danger in using an RJ-11 plug that provides power
for a lighted dial with a modem is if the modem is set up to operate with
RJ-12 or RJ-14 plugs.  See below for more information on these plugs.)

     RJ-41 and RJ-45S plugs are also "safe" to use with most all modems;
the exceptions may be modems which have RJ-12 or RJ-14 plugs.  See your
modem's documentation for details.

     If your telephone system is a multiple-line or "key" telephone system,
you must have a modem that is capable of interfacing with RJ-12 or RJ-13
plugs (such as a Hayes Smartmodem 2400).  The modem you use must also be
software-switchable to RJ- 12/RJ-14 operation.


                               Getting "Set"
                            DIP Switch Settings

     Most modems have user-accessible DIP switches (although the relative
accessibility varies from modem to modem).  DIP switches are used to set
various attributes of a modem, such as whether it waits for a carrier
detect before going online, etc.

     Some software packages require that certain modem attributes be set to
a specific state.  If your software has decent documentation, it will tell
you which states must be set, in which case all you have to do is refer to
your modem's documentation to find out which DIP switches are used to set
the attributes in question.  (Some software manuals will even tell you how
to set each DIP switch on the more popular modem brands.  Too, some modem
manuals provide specific instructions on DIP switch settings for certain
software packages.)

                           Rules and Regulations
                       Telephone Company Regulations

     Local telephone company regulations may vary, but in general the
following rules are in effect:

     *  Your telephone company should be notified that you will be
Using a Modem                                               Mike Banks - 3


connecting an FCC-registered device to your telephone line before you
connect it, and that you will be disconnecting the modem when you
disconnect it permanently.

     *  You cannot connect a direct-connect modem to a pay telephone, nor
to a party line.

                           Ventilation and Heat

     Don't use a modem as a bookshelf or repository for other materials.
While some external modems are designed to serve as a resting-place for a
telephone set, they aren't designed to be smothered by papers, disks, etc.
A modem's electronic components generate heat, which must be dissipated;
too much heat build-up can interfere with proper operation of the modem.
Therefore, heat vents--as well as most of the top of the modem--should be
not be covered.

                              Use the Switch

     If your modem is equipped with a power switch, use it to turn the
modem off and on.  Leaving the switch in the "ON" position and just
plugging and unplugging the modem's power supply is not a good idea; this
can occasionally create power surges or current overload.  When changing
the battery in a battery-powered modem, the power switch should be in the
"OFF" position, for the same reasons.

                           Overloading Circuits

     Don't plug your modem into an overloaded or faulty circuit.  Aside
from the fire hazard this creates, overloaded circuits often have low
voltage, and low voltage can cause excess heat and poor performance in your
modem.  (Overloaded circuits are typically those with too many electrical
devices plugged into them.)

                             Surge Protectors

     Surge protectors (also called "spike protectors") are an excellent
investment.  The purpose of a surge protector is to protect an electronic
device from surges in a power or telephone line.  Such surges are common
during thunderstorms and during periods when electrical power consumption
is particularly heavy.

     Power line surge protectors come in a variety of styles, but all
operate in the same manner.  Placed in the circuit between your computer
and/or modem and the wall outlet, they contain capacitors which absorb and
then bleed off excess power.

     Note that power line surge protectors come several configurations.
Some are simply small cylinders or cubes and offer only one receptacle.
Others are large rectangular boxes which mount on the wall in place of the
wall receptacle's cover.  These usually offer more than one receptacle.

     Some of the better surge protectors not only provide protection
against power surges, but also filter "line noise," and provide a circuit
breaker for protection against current overload.
Using a Modem                                               Mike Banks - 4



     Telephone line surge protectors operate on the same principle as power
line surge protectors.  Installed between a modem and its telephone line, a
telephone line surge protector absorbs then slowly discharges potentially
damaging voltage spikes.

                            Weather Conditions

     Never use your modem during a severe thunderstorm, nor at any time you
observe lightning.  Lightning is a guaranteed source of power surges in
both AC power lines and telephone lines--and, unless you have a surge
protector on both your modem's telephone line and power line, there's an
excellent chance that your modem and computer will be "zapped" by a current
surge.  (Even with surge protectors, there's no guarantee that lightning
won't damage your equipment.)

                                References

     There are several excellent books on using modems that expand upon
these topics with technical information.  These include:

     The Modem Book, by Michael A. Banks (Brady Books, 1988)

     Understanding Data Communications, by George E. Friend, et al (Howard
W. Sams & Co., 1987)

     Communications and Networking for the IBM PC & Compatibles, by Larry
Jordan and Bruce Churchill (Brady Books, 1987)

     Check with your local computer store for information on ordering these
books.

                                   (END)