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USRDUAL
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1994-03-29
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9-8-93 USR Modems
US Robotics Dual standard modems will support V32, the newer ones
V32bis. If the USR is a plain HST then the fastest connect will be 2400 as
the HST 9600 is proprietary protocol. Even when calling a Dual you may
often need to use one of the dial prfeixes to 'force' a connect at 9600 or
higher.
- - - - - - - - - - - - - - - - - - - - - - - -
Normal INIT for modems on a PC AT&F&C1&D2
Sometimes, even though the modem seems to get a good connect (usually
with hi-speed modem) it does not actually make the connection correctly.
(It may be the OTHER end making the error). Often if you use one of the
(prefix) strings to force that connect speed the connection will be made
'solid' on both ends.
V.32 / V.42bis Dialing Prefixes
The normal dial Prefix is ATDT. If the number is 423-1563 then it
sends ATDT4231563 to the modem, which then dials, and connects. This is
using auto-speed (baud) negotiation as well as negotiating Protocol
(V.42bis, MNP etc.). Some modems/software you will call do NOT like this.
Listed are alternate dial Prefixes you may use.
AT&Q5N1DT :negotiates SPEED and Protocol (default)
AT&Q6N1DT :negotiates SPEED only
AT&Q5S37=11N0DT :*Connect 14400, negotiate Protocol 2
AT&Q6S37=11N0DT :*Connect 14400 only 2
AT&Q5S37=9N0DT :*Connect 9600, negotiate Protocol
AT&Q6S37=9N0DT :*Connect 9600 only
AT&Q5S37=6N0DT :Connect 2400, negotiate Protocol (HST)
AT&Q6S37=6N0DT :Connect 2400 only (HST)
* for all V.32 modems
2-for V.32bis modems
NOTE 1: The above strings are using buffering which allows the computer to
have a higher speed than the modem. If you still have trouble try &Q0 in
place of &Q6 and set your computer speed the same as the modem speed.
NOTE 2: I discovered when a user couldn't connect to a 300bps modem, that
if I did AT&F (set &C0&D0) before using the dial prefix, then it would
connect. This is worth a try on stubborn 1200bps modems too.
Connect result messages / modem speed
S95=44 gives you full result messages with CONNECT (modem to computer
speed). If you need CONNECT (modem to modem) speed the same as CARRIER
(modem to modem) use S95=45. When running a BBS, try S95=3 and you will
get only CONNECT(carrier) message, with \ARQ for error correcting modems.
Always set your 'speed' in your program to the highest permissable
computer - to - modem speed (check your manual). The V.32xx or V.42bis
modem will take care of modem to modem speed.
Don Hinds - Zoom Tech
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