Tandy Professional Forum   Section: T1000/1400/3000/4K
Subject: Hi-speed modems   Total messages: 5
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#62438   2 Replies   09/05/96   19:03:04
From: Paul Hanke, 73467,403
To:   Robert A. Hengstebeck, 76417,2751

If you can get 57000bd on a 28800bd modem that's pretty good;
must be using data
compression....?  What about the Uart chip - I've been hearing
that a 16550AF
must be present or at least emulated; what happens if there's
only a 8250 Uart
in the computer - can it be replaced easily, and inexpensively -
and is a
16550AF really necessary?

I've had a problem using the modem with a dos telecom program; it
gives a
'waiting for CTS signal' error and won't connect.  Usually this
occurs if I try
to access the program directly after booting.  If I use a Windows
telecom
program first, to log on at least to the point of a dial tone, I
find I can
sometimes use the dos program from that point on.  It seems that
the modem first
wants to be initialized by Windows programs, then it will respond
to dos.  -ph


#62440   Reply to #62438   09/05/96   21:27:24
From: Robert A. Hengstebeck, 76417,2751
To:   Paul Hanke, 73467,403

Paul, What I have is a WinModem, but I wouldn't recommend them
after the experience that I went thru to get it to work on my
Tandy 3200.  This computer is a 486sx, but its construction is
similar to the 2500sx.  I have space for three expansion boards
placed in sidewise.  I am using two of the slots, the first being
the modem, the second is the creative labs sound blaster.  All
high speed modems, have the high speed uart built into them. I
will say again, stay away from any WinModems, especially the one
from US Robotics.  As far as your experience goes, it certainly
sounds like you got one of these beasts.  If you can take it
back, and get a modem that doesn't require drivers either for dos
or windows, do it.  The modem that I have has drivers but it took
many months of experiments to find ways to get it to work under
different conditions, especially the program TAPCIS which is a
DOS program, and also when I am using OS/2 as an operating
system.  Also the experience that you described, about connecting
at high speeds in a reliable manner is one that I experienced on
four other modems.  It seemed like a constant return trips to the
stores before I found one that I could use reliably.  That one
that I ended up with was a US Robotics 14,400.  But this is not a
WinModem, and I had no problem with it at all.  It would have
been adequate for me, but since I wanted to experiment with the
Internet, I felt that I would need a faster modem.  Unfortunately
for me I had no fore-warning about the problems that I was going
to go thru.  Those problems I do not wish onto anyone else.


#62446   Reply to #62438   1 Reply   09/07/96   06:16:10
From: Horace Ory, 71625,1006
To:   Paul Hanke, 73467,403

With an 8250 UART 9600 bps is about the best you can do; at
14,400 bps the error rate reduces throughput to less than you get
when operating at 9600 bps.  A 16650 (or 16640) provides
buffering that allows much higher bps and throughput.  Higher
throughput than the indicated bps can be obtained through various
compression techniques.  High speed internal modem usually have a
16650 UART built in.  Many computer serial ports, to which an
external modem would ba attached, use an 8250 UART.  You can get
cards (I/O or combined with disc controller functions that have
16650 or equivalent UARTS and replace the one now in the
computer.  Usually either or both modems and communications
software can be configured to use hardware (RTS/CTS) handshaking
rather than other forms, and you can check into configuring
yours. Windows tends to select hardware handshaking as the
default.


#62447   Reply to #62446   1 Reply   09/07/96   08:27:27
From: Paul Hanke, 73467,403
To:   Horace Ory, 71625,1006

I like the practical use of an external modem, ie, being able to
switch it to
another computer for temporary applications; and at the same
time, free up an
expansion port. My 3 ports on the 4825SX are now filled (scsi
cdrom card, sb16,
and 14400fax/modem).  Is there any other way to upgrade to a
16650 UART without
having to buy another card, which would fill up the slots again?
 Is there an
easily removable 8250 chip on the 4825 (I'm no stranger to
soldering irons)?
Maybe direct substitution is not feasible/practical....?   -ph


#62452   Reply to #62447   09/08/96   03:10:08
From: Horace Ory, 71625,1006
To:   Paul Hanke, 73467,403

If your I/O card is separate from the motherboard, you can
replace it fairly inexpensively with one that has a 16650.
That's what I did. Actually, my I/O is on an IDE controller card,
which I replaced for around $20.  If your serial ports are on the
motherboard, a direct chip replacement is probably not practical.
 However, your may be able to disable the motherboard ports and
add an I/O card, perhaps to replace your internal modemand go to
an external modem.  I also prefer an external modem.  It provides
a little more electrical protection than an internal one against
telephone line power surges (such as from a nearby lightning
strike).  Also, I use more serial devices (modem, printer, mouse,
packet radio TNC) than I have ports, so connect them through a
switch box and select the ones I need at any given time.


