-=> Quoting Robert Osborne to Rick Collins <=-
-=> FidoMail to 1:163/215, please.-=<
rc>rc> to have jumpers to select the RC>comm port and IRQ, even if
rc>rc> they also support "plug and play". 
ro> I take it that "Plug and Play" is an extra added feature to the
ro> new modems and not a prime concern to get them to work on any
ro> machine not having the required bus and board slots on the
ro> mother board? 
Correct.  Many think "plug and play" should be called "plug and
pray", because often the vaunted "feature" doesn't work properly -
especially with older hardware.
RC>You don't have to configure the external modem at all
ro> Am I using the wrong words here? May be I should have said
ro> initialize? When you configure your communication software such
ro> as Telix, you have a lot of choices such as setting the baud
ro> rate and modem. Are you not configuring your modem thru this
ro> process whether it is an external or internal? Are you also
ro> configuring your computer's ports?. 
Maybe I'm using the wrong words. :-)  You have to configure the modem
through a configuration string, yes.  But you don't have to worry
about the comm port and IRQ when dealing with the *modem*, because
they're part of the PC itself.  You _do_ have to properly configure
the comm port _as well_ as configuring the modem, though.  What I was
trying to get across (abysmally, it seems) is that you don't have to
futz with comm port settings and IRQ settings somewhere inside the
external modem, but rather inside the PC.
rc> RC>to make sure the computer has a comm port properly configured,
rc> and RC>you plug into that. Most PCs support two comm ports,
rc> Com1 and Com2. RC>If you presently have an internal modem on
rc> Com2, when you remove it RC>you will have to enable the Com2
rc> port in the PC (it would have to be RC>disabled to allow the
rc> internal modem to work on Com2). So, with an RC>external modem
rc> you have to configure the port, not the modem. 
ro> In other words you are changing it back to a Serial Port to I/O
ro> with the external? This change is not done thru the
ro> communication software right? It is done thru the operating
ro> system. Explain briefly please? 
Okay.  Your PC hardware usually comes with two hardware comm ports
(serial ports), and DOS will support four comm ports, called com1
through com4.  Generally, the hardware ports are configured as com1,
IRQ 4 and com2, IRQ 3, and no actual hardware is provided for com3
and com4.  Each comm port has a base address.  When DOS or a DOS
program tries to do something with a comm port, it accesses this
address where it expects to find the actual port hardware.  The
hardware on the comm card is configured to use the default addresses,
but _some_ cards allow you to change not only the "port number"
(1,2,3 or 4) and the IRQs (3,4,5,7), but _also_ the base address of
each port.   That's why Telix allows you to select not only the comm
port and the IRQ, but also the address of that port.  Usually,
though, the default address is correct and often can't be changed on
the actual hardware port.
Now you can't "share" a device address - each device must have a
unique address, and generally, you can't "share" an IRQ, either.  So,
if you install an _internal_ modem configured for Com2 IRQ 3, you
must _disable_ the hardware comm port that is in the PC and assigned
to Com2.  That meets the "one device per address" rule.  OK, you do
all that, and use your internal modem.  Then, you replace it with an
external.  At that point you have to remove the internal modem (which
was using com2 IRQ3) and _enable_ the internal port that you
initially _disabled_ when you installed the internal modem. 
Alternatively, you could change the jumpers on the internal modem to
(say) Com3 IRQ5 (IRQ5 is usually unused on most systems) and then
enable the com2 port.  That would permit you to use the external
modem on com2 (through the hardware port 2, using IRQ 3) _and_ the
internal modem on com3 using IRQ5.
rc> RC>If you're running a recent version of DOS, try typing MSD at
rc> the DOS prompt. That will run the MS Diagnostics. Select
rc> Comm Ports from the menu and the available ports will be
rc> displayed. Note MSD will treat your internal modem as a comm
rc> port. 
ro> OK! I can see that. What are the key things of importance from
ro> this display. I can see the UART chip type is significant. 
ro> This has to do with its speed right? What about the address and
ro> other items listed? What should I be concerned about as to
ro> configurations and getting the modem to work? 
In that display the UART type is significant: if it reads 8250, and
you have a modem connected, you should replace the UART with a 16550. 
Your internal modem should show a 16550 type UART.  Each device shown
must have a _different_ "base address" (they will if they're
displayed).  The IRQ assignments are found in another screen labelled
IRQs from the main menu, and you should see an IRQ assigned to both
com1 and com2, and they should be different.
rc>That's still common. Most plug-and-play internal modems can be
rc> manually configured using jumpers, and usually that will work
rc> better than relying on Windows to properly configure the modem. 
rc> If you buy a plug-and-play internal, make _sure_ you can manually
rc> configure it if necessary. 
rc>ro> Even if I do configure the internal by jumpers I still run the
rc>ro> risk that the Windows SW won't reconfigure its files to the
rc>ro> new modem right? 
No, that shouldn't be a problem.  If you disable the "plug and play"
and use the jumpers, you must tell Windows what port and IRQ to use
with the device, and Windows will use whatever you tell it.  It's up
to you to make sure there are no conflicts, though.
ro> When you are using the Win 3.1 program, do you have to disable
ro> the PC com port so the modem can be seen before you load the Win
ro> 3.1 program? 
If you're using an internal modem, yes.  You can't have two devices
selected by hardware to use the same addresses.
rc> Chances are you won't see an 8250 (they're old), but the 16550
rc> is a standard part, and they are a direct replacement for an
rc> 8250 or a 16450. No special card required. 
ro> I looked at my current 2400 baud modem via the "msd" command. It
ro> has the 8250 chip. Would it do any good to replace it with the
ro> direct replacement? What would be the advantage? 
MSD can't distinguishe between a 16450 and an 8250 - it calls them
both an 8250.  Most likely the UART on your old internal modem is a
multi-function chip and therefore you can't replace the "UART
portion".  It wouldn't make any difference, anyway:  the 8250 is all
that is required at 2400 bps, and a better UART won't change things
at all.
ro> Does the way you have your Computer's Operating System configured
ro> directly affect the speed of the transfer of data from files
ro> being up loaded or down loaded by the system as a whole? IE
ro> disk access time, or memory available etc. 
It could, but not significantly in most cases.  Most comm programs
use default settings for disk buffer sizes and so on and there
usually is no need to change them.  The only time this is _not_ true
is when using an unbuffered (not 16550) UART at high speed and a disk
write cache, like SMARTDRV.  The cache writes less frequently to the
disk, but writes more data when it does access the disk.  That opens
the possiblility of a "delayed interrupt" and trashed data which will
require a re-send, lowering your throughput.  The 16550 cures that
problem.
RC>The modem is generally configured to connect at its fastest speed,
RC>and it negotiates the speed with the remote modem.  That's almost
RC>completely out of your control, and not your concern.  You simply
RC>make sure your port speed is set _higher_ than the modem's maximum
RC>speed:  either 57,600 or 115,200 bps for a 28,800 bps modem.
ro> Please explain the difference between "Port Speed" and "Modem
ro> transmit speed"? How are they set? Is the Port Speed what you
ro> set in the Communication program such as Telix? Is this the
ro> maximum rate the computer will handle bytes coming off or going
ro> to the serial board or internal modem? 
You set the port speed in your comm program, and it controls the
speed at which data flows between the PC and the modem (internal or
external).  The "modem speed" is the speed the modem connects to the
remote modem at, usually called the CONNECT speed.  You control the
port speed, but the modems themselves negotiate the connect speed.
ro> If you buy a used modem today, what vintage would you look for to
ro> expect to see all these new improvements. Ie compression and
ro> error correction? Is both the compression and the error
ro> correction done thru the "Chip Set" on the modem? or do you have
ro> to run special accompaning software on the computer to get these
ro> features to work? 
All 14,400 and faster modems can be expected to have error correction
and data compression, and all 28,800bps and faster modems have that
built in to the modem hardware.  Some 14,400 modems require comm
program or Windows comm driver support for these features, and are
called "RPI" modems.  Avoid them.  Modems advertsied as "WinModems"
or designed solely for use in Windows generally use the PC for most
of the modem functions, including compression and error correction,
and will not work outside of Windows.  I'd avoid those, too.
ro> If you have not already explained the port speed you mention here
ro> please do so now. Also does the vintage of the processor in any
ro> way effect port speed? Since the highest modem bps that I have
ro> seen is 57 K bps, does that mean that a 8 MH processor should be
ro> able to handle the thru put with no problem? Or is it a
ro> function of the type of software "OVER HEAD / DEGRADATION" you
ro> are running that will drastically reduce you systems capability
ro> to thru put at that rate. Am I forced to go to a higher speed
ro> processor and GUI (graphical user interface) to be able to use
ro> the newer modems and be able to access the internet or an on
ro> line service? 
Even the slowest CPU can keep up with the data rate from the fastest
available modems.  If you intend to use a Windows browser for the
internet, though, you'll want a faster processor.  The system can
easily keep up with the data rate from the modem, but probably won't
be able to display the data quickly enough to make the experience
pleasureable. :-)
TTFN. Rick.
Ottawa, ON 26 Jun 16:41 
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