ptownson@delta.eecs.nwu.edu (Patrick A. Townson) (06/02/91)
I have quit using my US Robotics Courier 2400 modem and am now using a
Telebit T-1600 instead for my work (and play) on the net. It generally
works quite well, but one problem bugs me:
Configuration:
I use the 'tty' mode (AT&F0), with a couple differences from the
factory defaults. I have S254=0, although Configuration A and B are
identical.
I use AT&D2, with the modem responding to DTR going up or down.
I set S51 (DTE interface speed) = 253 (autobaud, default to 38,400).
I set S61 (Local action on break) = 0, rather than its default of 1.
The default says pressing the break key will put the modem in command
mode. (This is in addition to use the of '+++' to do the same thing?)
My problem is I need to use the BREAK key occassionally to get out of
a trap when on line at eecs.nwu.edu. There are times (in emacs, quite
often) when everything stops. I can't get out, nothing responds, and
the only solution is by hitting the BREAK key I at least get dumped
out back to the server ... so I wanted to keep the BREAK key for my
own use.
Since S61=0 (break is processed as defined in register 63), I then
set S63=1, (send break immediatly).
S180=2, the default (error control is V.42 with detection).
S190=0, (Data Compression Enable) is turned off. The default is 1, to
enable in both directions.
I use the modem almost exclusively in an interactive situation,
typing at the terminal. I rarely download/upload big files. Mainly
I wanted the screen refreshes to be faster ... and they are much
faster than with the old 2400 baud unit.
The only thing Data Compression does is causes a 'jerky' effect as
the stuff being transmitted is put in packets, etc ... I did not
need it so I turned it off.
Otherwise, the registers are all set to the factory default.
The problem: using three plusses to go to command mode works okay in
getting me there, but I can't get back on line.
Using the BREAK key to do this (by setting S61 back to the 1 default)
works okay ... I go to command mode, and ATO puts me back on line.
Using the three plusses gets me into command mode, and ATO *says* I am
back on line (produces the CONNECT 9600 message), but nothing actually
gets from the DTE to the modem and on to the distant modem at that
point.
I tried ATO1, which the manual says 'retrains equalizer before going
back on line'. ATO is also possible to go back on line without
retraining.
Once I have 'three plussed' into command mode and did ATO or ATO1 to
go back on line, my only option at that point is to disconnect
entirely and dial back in.
I could see this happening if I changed some registers while in
command mode, or otherwise got the modem confused, but I've tried this
doing nothing other than 'three plussing' into command mode and
immediatly issuing the ATO or ATO1 to get back out ... and it still
fails to reconnect.
Finally, after plussing => command mode => ATO => back on line, but
with an unresponsive modem and typing blind (nothing at that point
comes back to the screen), if I three plus again, the three plusses do
not show up on the screen, but the modem does act on them by putting
me back in command mode again.
We wondered: does this problem only occur at 9600 baud?
Logging in at lower speeds (1200/2400 baud) on the same unix
machine got the same results ... three plusses into command
mode, then ATO back on line, but typing blind and no response
from the modem except for the entry of three more plusses.
Logging in at lower speeds to MCI Mail / AT&T Mail and a couple
local BBS' did **not** produce this problem. When on those sites,
the three plus => command mode => ATO back on line worked fine.
Unfortunatly, the mail services and the local BBS' here do not
support 9600 baud (that I know of) so I could not test the
higher speed there.
Can anyone suggest a solution?
Why will BREAK => command mode => ATO (ATO1) => back on line work
fine at any speed on the T-1600, but the three plusses exit to
command mode fail to go satisfactorily back on line, causing blind
typing and no response?
Why does this occur when calling this unix site, but not when
calling MCI Mail (for example)?
Thanks for answers.
Patrick Townson
gandrews@netcom.COM (Greg Andrews) (06/03/91)
In article <1991Jun2.141605.5766@eecs.nwu.edu> ptownson@delta.eecs.nwu.edu (Patrick A. Townson) writes: > > [long description of modem configuration deleted] > >The default says pressing the break key will put the modem in command >mode. (This is in addition to use the of '+++' to do the same thing?) > Yes, provided S61, S2 and S12 are at their default settings, you can get to the modem's command mode by sending a Break or by typing +++. > > [description of reasons for break signal settings deleted] > >The problem: using three plusses to go to command mode works okay in >getting me there, but I can't get back on line. > >Using the BREAK key to do this (by setting S61 back to the 1 default) >works okay ... I go to command mode, and ATO puts me back on line. > >Using the three plusses gets me into command mode, and ATO *says* I am >back on line (produces the CONNECT 9600 message), but nothing actually >gets from the DTE to the modem and on to the distant modem at that >point. > The problem is with the modem on the other end of the phone line. That modem does not have its +++ handling disabled as it should. Here's what happens: You type the +++ hoping to get your modem to drop to command mode. As you type the three plus signs, they are passed to the host. The host echoes the three plus signs so they will show up on your screen, just like any other keystroke. So the three plus signs you typed (and the pauses before and after) are transmitted by your terminal **and by the host**. Your terminal transmits them as you type them, and the host transmits them as it echoes your keystrokes. As you can see, BOTH modems see the +++, and they will both drop to command mode. You have control over your own modem, and can bring it back out of command mode. You don't have control over the host's modem, so it stays in command mode, where it can't pass data. The host modem should be configured to ignore the +++ escape sequence so it won't cause this trouble. Hosts don't normally echo Break signals, so that's why the Break method worked. Besides, your modem wasn't passing the break to the host when S61 was set to go into command mode. > [description of various tests deleted] > > Why does this occur when calling this unix site, but not when > calling MCI Mail (for example)? > MCI has configured their modems properly for unattended dial-in. > Patrick Townson -- .------------------------------------------------------------------------. | Greg Andrews | UUCP: {apple,amdahl,claris}!netcom!gandrews | | | Internet: gandrews@netcom.COM | `------------------------------------------------------------------------'