what's all this about UART chips and cable types?
for reassurance here, your modem is external if the phone line plugs into a
separate box which is then connected to your computer. You have an internal
modem if your phone line plugs directly into the back of your computer.
that said, we can now get a little more technical.
chips come in varying performance. Most common here are (listed highest to
lowest performance) 16550, 16540, 8550, and 8250.
you have the Microsoft program 'msd.exe' on your system, you can run it from
the command line and check out what kind you have if you don't know or don't
have the manual for your serial port (com port).
you have an external modem...
want to know what kind of UART chip your system is using (Note: This applies
to PC's and not Mac's).
you have a high speed modem (14400 or higher), and a multi-tasking OS (such
as Win'95), you should be using a 16550 UART.
16540 UART is technically OK to use, but does has limited performance over
a 16550 UART.
also want to make sure you have a good cable. Some cables are not made for
use with a modem and cause problems (especially when using RTS/CTS or "Hardware
Handshaking"). The cable may be leaving out certain pin-to-pin connections
that will i mpair your connection.
really no way to test this for certain over a phone line, or even by the physical
appearance of the cable, but, some cables are thinner or thicker in appearance.
It's a good sign (but not definitive) if your cable is about 1/4" thick, rather
than a slimmer 1/8" inch cable. The 1/8" cable is a sign that it is a "null
you have an internal modem...
the modem is internal, then it uses it's own UART and this shouldn't be a problem
(unless of course it is newer than Methuselah).
you have a PC...
may have a diagnostics program to look at your com ports and UART chip.
you are running Windows 3.*/MS-DOS or if you have an "UPGRADE" of Win'95 (where
you would have upgraded over an existing Win3.*), you should be able to boot
to a DOS prompt and run msd.exe. Running this from a DOS shell under any Windows
environm ent may cause incorrect data to be reported.
you have a Mac...
absolutely sure you have a "hardware-handshaking" modem cable. If you're using
the cable that came with a 14.4 kbps or 28.8 kbps modem, there's a good chance
that it is a hardware-handshaking cable. However, most store salesmen and mail
order cl erks know little about Macs and even less about the Internet. There
is simply no way to tell just by looking at a cable whether it is a "normal"
modem cable or a "hardware handshaking" cable. If your cable didn't come from
the modem manufacturer, sealed in the same box as your modem, and if the box
and documentation don't specifically say that the cable is a MACINTOSH "hardware
handshaking" or "hardware flow control" or "high-speed" cable, your best bet
is to assume that you've got an new-style cable. Trying to set up a direct
Internet connection with the wrong kind of cable is a guarantee of extreme
CAN buy a decent cable at a good computer store if you make an issue of it.
It should cost around $15 to $20, depending on quality. The cable should connect
pin 1 on the 8-pin end (the Mac end) to pin 4 AND pin 20 on the 25-pin end
(at the m odem). Ask the salesperson to have one of the service technicians
do a simple connectivity test. (You can do the same thing yourself with a connectivity
tester.) If you get a cable that doesn't connect those three pins together,
it won't work. If you g et one that does, there's a good chance it will work.
your connection 'idle' or have you rebooted the computer/reset your modem?
drivers, TCP/IP drivers, UART settings, and Modem drivers can become corrupt
in memory. Sometimes rebooting your computer and resetting an external modem
(by power-cycling it) will reload the driver(s) in an improved state (unless,
of course , the driver is corrupt on the disk at which point removing it and
loading a fresh copy would be the solution).
also will cause your computer to 're-initialize' your modem.
you having connection problems with an E*Machine?
following link, will take you straight to E*Machine's modem technical support
page. Full of tips, and other info on troubleshooting the PC-Tel modems which
most E*Machines come with.
can put an extra command string in "Advanced Setting" in Modem Properties to
resolove this problem most of the time.
for v.90 compatibility
for K56Flex compatibility
for basic V.34 compatibility.