On Sep 09 14:41, 1997, Blair Thompson of 1:109/621 wrote:
BT>   Amazingly enough, in two weeks I bought two USR 14.4 modems, one used 
BT> (USR Mac&Fax), and one new (the previously mentioned USR 14.4). The new 
one 
BT> has its factory settings still in place, but I have been unable to use it 
BT> yet, as I cannot get my 286 to recognize COM2. The computer is a brand 
name 
BT> Laser. There is a 10-place DIP switch on the motherboard. I got the 
BT> computer secondhand too and have no documentation to tell me which switch 
BT> to change. With 2**10 possible settings, I'm going to try to look up some 
BT> reference works first.
BT>  The Mac modem's previous owner used it on a Powerbook, so its DIP 
switches 
BT> have been changed; #1 is down instead of up. I'm using it on a Performa 
to 
BT> write these words, and as they say, if it ain't broke, don't fix it. I'll 
BT> probably give in to curiosity and return the switches to factory setting 
to 
BT> see what happens.
Switch 1 (normally OFF) is DTR - Data Terminal Ready override.  When the 
switch is OFF, the modem will recognize DTR, which must be asserted (by the 
PC) for the modem to recognize commands.  Most comm programs "drop" the DTR 
line to hang up - the modem will disconnect when DTR is dropped.  When ON, 
the modem ignores the state of the DTR signal.  Dropping DTR is a better 
"hang up" method than ATH0, because ATH0 requires the modem first be put in 
"command" mode before the command can be issued.  The hangup is usually 
faster using DTR.
On the 286 - it's quite possible there is only _one_ comm port on that 
machine on the motherboard.  Easiest way to tell is to look for the 16450 
(likely) or 8250 (less likely) UART - they'll be labelled with those numbers. 
 If you find two of them, you have two ports.  If there is only one, your 
best bet is to buy an external I/O card with two ports and use that instead.  
Make sure it has a 16550 UART for the modem.
Rick
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