FREQUENTLY ASKED QUESTIONS
Last updated: 5/28/01
Q. How can I test the serial port and cable connected
to an external MODEM?
A. There may be a diagnostic program that
came with the MODEM, if that is what you are connecting to. A MODEM
that uses the Hay's AT command set (most do) can be tested by simply echoing
an AT command at the DOS prompt and redirecting it to the COM port, e.g.,
C:\>ECHO ATDT > COM1
Should cause a MODEM on COM1: to pickup the phone line
and you should hear dial tone from the MODEM.
C:\>ECHO ATH > COM1 USING ECHO
...should cause it to hang-up, killing the dial tone.
Doctor is a useful MODEM diagnostic shareware program that will
check both ports and MODEMs.
Windows 9x/Me has a MODEM Diagnostic at Start, Settings
Control Panel, Modems, Select the MODEM, Diagnostics tab, select the port/MODEM,
More Info. In Windows 2000: Start, Settings, Control Panel, Modems
tab, Properties, Diagnostics, Query Modem.
MODEMs can be tested by dialing a local Internet Service
Provider with Windows Hyperterminal (I used to dial a local bulletin board). You
can pretty much tell whether the serial port and cable are working or not
by typing something in the Windows HyperTerminal and looking at the LEDs
on the MODEM. AT commands can be issued from HyperTerminal as well. The
MODEM should respond to AT with OK. ATIn should displays the
MODEM's manufacturer information for n = 1 through 7. This provides
information such as the port speed, the result of a checksum test, and the
model information. Check the manufacturer's documentation for the expected
MS Diagnostics (MSD) that comes with Windows 95 and MS-DOS
6.X is useful for determining if a serial port is responding (it is also
on the Windows 98, 98 Second Edition, and Windows Millennium Edition CD's
where D: is your CD-ROM drive letter).
A loopback test, which requires a loopback plug/adapter,
is a very good test of a serial port. Several commercial diagnostics
programs (e.g., AMIDiag)
come with a loopback plug. When a loopback test is run data is sent out the
serial port’s transmit pin to the loopback plug which sends the data back
to the port’s receive pin. This test assures the 1488 and 1489 buffer chips
or equivalent are working and they are the chips that are usually damaged
by a close lightning strike, etc. Scott Mueller’s Upgrading and Repairing
PCs has more info and instructions for making a loopback plug. Just search Google for
the book. Every shop should have a copy. However, the best and easiest
to read shop reference on serial ports and cables I know of is Data Communications
for Microcomputers by Elizabeth A. Nichols, Joseph C. Nichols, and one of
my business acquaintances from the old days, Keith R. Musson, McGraw-Hill
1982. I think it is out of print.
breakout box and a multimeter are useful tools for troubleshooting
serial ports and cables.
Q. How can I quickly run a speed test on MODEM?
A. Search google.com with modem speed test
to find various web sites that test MODEM speeds.
Q. My AOpen FM56-P modem auto selects IRQ0 and
COM3. No way to get around these settings. Running on ASUS P2B-F AGP Motherboard.
Best speed is 33.6K. Somehow V90 is not working. Can you help?
A. A MODEM using IRQ0 (the one used by the
System Timer) is a problem I haven't seen before. Try forcing the MODEM to
use another COM port. Power-down, pull the MODEM, power-up, go into the CMOS
Setup, Go into Plug 'n Play, Set it to Manual, Assign, IRQ 3 to Plug 'n Play
from Legacy/ISA, go into Integrated Peripherals, disable Serial Port 2, Change
Serial Port 1 to 3BC/IRQ 4 (to stop the MODEM from using it), power-down,
plug-in the MODEM, power-on. The idea here is to block COM3 and , hopefully,
push the MODEM into COM2: where it belongs.
How do you know the MODEM isn't or trying to talk V.90? Theoretically,
you have to be within four miles of the telephone switch (exchange - not
the ISP) to go from analog at 33.6 to digital at something less than 56K.
V.90 MODEMs can not operate at 56K. It is illegal. The fastest they can go
is 53K. I have never seen one go faster than 49K and my store is less than
a mile from the telephone switch. I have seen them go faster than 33.6 at
distances greater than four miles, however. Is your ISP set-up for V.90? Are
you using the right phone number for your ISP's digital dial-up? Some
ISP's have different phone numbers for analog and digital connections. What
is the maximum speed showing in the MODEM properties? It should be
Q. My Aopen
FM56-ITU Modem keeps disconnecting within 30 seconds to about 2 minutes
when online. I have no trouble with my US Robotics modem. I try the FAQ's
and newsgroups on Aopen's web site and see the same complaint from other
people. Please tell me how to fix this problem.
A. My guess is you have a bad MODEM, IRQ conflict,
noisy phone line, or a compatibility problem with your ISP--in that order.
Try a dial-up to another provider. Your ISP is running V.90 or K56flex, right?
X2 will work with a US Robotics MODEM, but it will not work a FM56-ITU. If
your ISP has not updated to V.90 by now I would get a new one. I have
had very good luck with the FM56-ITU MODEM.
Q. I have a RCVDL56ACFW/SP MODEM and wondered
if you know of where I can get the Windows NT 4.0 drivers for it?
A. That is the Rockwell chip on the MODEM. You
will need the MODEM Manufacturer and Model. With that info you can
probably locate the manufacturer on our Manufacturer
Links page or with a search engine, and download the drivers from
the manufacture's web site. How
to Identify a Motherboard has some tips which can be used to identify