96-33

To: All LINK Libraries
From: Greg Barniskis, SCLS Network Administrator
Date: June 27, 1996
Re: Isolating VT100 display problems from Gateway problems

There are a number of known "behavior" problems with Wyse terminals using VT100 emulation. Some of these problems originate with the Dynix software, and those are easy to fix. Other problems originate with the use of the Gateways module and will be somewhat more difficult to fix. The biggest problem we face in getting VT100 terminals to work smoothly is determining the origin of any particular display problem.

All telnet servers (except for the very simplest) use control characters to tell your terminal how to behave -- how to draw lines, where to put text on the screen, what attributes the text has (bold, reverse video, etc.), and more. Quite frequently, the control characters are paired, where one turns a terminal behavior "on" and another turns that behavior "off". If the server sends the wrong characters, or if the terminal misinterprets a character, the terminal can get confused about what it is supposed to be doing. Sometimes this confusion results in a visible parameter change, and sometimes it does not. Sometimes the confusion does not go away until the terminal is reset.

So, how do you know if a display problem is being caused by the function you are using (say, placing holds in Dynix), or is a leftover problem from a control character received earlier in the day? There is no way to answer this question without a testing process that eliminates the second possibility.

Before doing any more testing, please log off and do a complete parameter check on all of your VT100 terminals. The parameters for a VT100 terminal are all the same as shown in the Troubleshooting Manual for a regular terminal, except for F2: Personality = VT100. Save the parameters, then perform a terminal reset (Control-Shift-Setup).

After making sure all your terminals are correctly set up, go through the following steps each time you encounter a VT100 behavior problem.

I. Check your parameters. If parameters have changed, write down which ones and what values they have changed to.

II. Fix any parameter problems, then try to duplicate the display problem.

III. If you can duplicate the display problem, write down as much information as possible about the problem, including bar codes or record numbers, and the sequence of steps that lead up to the problem, then continue with these instructions. If you can't duplicate the problem, there is no need to continue with these instructions -- forward information about parameter changes to me at (608) 266-6394, through delivery or through LINKcat mail.

IV. Log off your terminal.

V. Perform a terminal reset (Control-Shift-Setup).

VI. Perform another terminal reset (Control-Shift-Setup). This is really only necessary in extreme cases, but it doesn't hurt, so do it every time.

VII. Log back in and try to repeat the problem again. If the problem recurs, this indicates a basic conflict between a LINKcat function and the VT100 emulation. If it does not recur, this indicates a problem with terminal "confusion" that was fixed by resetting the terminal.

VIII. In any case, report the results of this testing to me and I'll see what I can do about fixing things so the problem doesn't recur.


In the special case of a "confused" terminal, we need to find out where the behavior change originates. Odds are that there is a problem with using a particular Gateway menu item, or with using a particular feature of one these telnet servers. These problems will be difficult to pin down, but the only way to clear them up is to watch very carefully what happens to your terminal after using a Gateway. Any specific information you can provide about the circumstances surrounding and preceding the behavior change might be useful in isolating the problem.

When the source of any VT100 problem is pinpointed (either with LINKcat or with Gateways), I will send a notice via LINKCAT mail so that you can be aware of it and work around it until it gets fixed.

As of this writing, there is only one problem that has been accurately pinpointed. As your terminal is being logged in, it negotiates with the system for VT100 emulation. During this negotiation, the terminal learns how to draw the lines that enclose "windows" on the screen such as the box that encloses the list of hold pickup locations. If your terminal is reset or powered off, it loses this information and you will see "q" and "x" in place of the nice line drawing characters. The only way to fix this is log off and log back in.