[comp.os.vms] VT100 confused by TPU

sdowdy@charon.unm.edu (Stephen Dowdy) (12/16/87)

I am designing a minimal pager mechanism in TPU and have come across
a problem.  The pager, so far, works fine on all DEC crts that i have
tried, except for VT100's marked VT100-AA.  If i page up and down
several times, the vt100 gets extremely confused about what its
scrolling region is and where to put the next line of text.  This
problem persists even upon exiting TPU.  Doing something like
$ DIR/COLUMN=1	! or any command with plain text output
cause the screen output to jump from one line to another without
much relation to screen order.

I can get rid of the problem by SET TERM/NODEC_CRT, but this causes
a significant loss in screen efficiency.  (many users will probably
be running at 1200 baud, and redrawing the screen for single line
motions is not really acceptable).

Has anyone else noticed this problem (i assume it is just a non-compatible
firmware version in an older vt set) and does anyone have a solution
or work-around? (other than "get rid of the terminals", or "convert to unix");

--stephen dowdy

cfchiesa@bsu-cs.UUCP (Christopher F. Chiesa) (12/18/87)

In article <2080@charon.unm.edu>, sdowdy@charon.unm.edu (Stephen Dowdy) writes
> If I page up and down
> several times, the vt100 gets extremely confused about what its
> scrolling region is and where to put the next line of text.  This

This sounds somewhat similar to what I experience when using a DEC GIGI
terminal ("so awful they had to name it twice...") in such things as Vax
DEBUG...  {I dial into our Cluster at 1200 baud and DEBUG does indeed "re
draw the screen for single line motions..." - several times for EACH command
executed}  - because the GIGI doesn't HAVE "scrolling regions."  What a pain.

  Well, anyway, my thought is this: write a test program (something to "echo"
each character you type right back to your terminal) to examine your
terminal's response to individual "set scrolling region" and other escape-
sequence commands - it sounds like your terminal's behavior is just plain
"at odds" with what it "should" be.  Does what you describe happen on ALL
"VT100-AA" terminals, or just YOURS?

  I've used this "echo program" idea to "de-mystify" several terminals, and
although it can be slow, it usually does work.  (A general-purpose DEC 'ter-
minal test' program would be nice, something that you run and then compare
your screen output with examples in a manual, saying "if you have THIS dis-
play, your terminal has such-and-such problem", maybe.)  Good luck - I hope
you're able to work it out.

   Chris Chiesa, BSU CS Dept. student

ted@blia.BLI.COM (Ted Marshall) (12/23/87)

In article <2080@charon.unm.edu>, sdowdy@charon.unm.edu (Stephen Dowdy) writes:
> I am designing a minimal pager mechanism in TPU and have come across
> a problem.  The pager, so far, works fine on all DEC crts that i have
> tried, except for VT100's marked VT100-AA.  If i page up and down
> several times, the vt100 gets extremely confused about what its
> scrolling region is and where to put the next line of text.  This
> problem persists even upon exiting TPU.  Doing something like
> $ DIR/COLUMN=1	! or any command with plain text output
> cause the screen output to jump from one line to another without
> much relation to screen order.

My memory is somewhat fuzzy, but since no-one else has said anything, I will
see what I can dredge-up.

As I recall, there was a firmware bug in at least some VT-100's. I think it
had to do with scrolling regions under soft-scroll. I remember that it could
be pushed far enough that the terminal did a full reset.

I don't know if this was fixed in later versions of the VT-100 family (I assume
so) or what models/serial-numbers had the problem. However, I do remember that
turning off soft-scroll mode fixed it. Try that.

-- 
Ted Marshall       ...!ucbvax!mtxinu!blia!ted <or> mtxinu!blia!ted@Berkeley.EDU
Britton Lee, Inc., 14600 Winchester Blvd, Los Gatos, Ca 95030     (408)378-7000
The opinions expressed above are those of the poster and not his employer.

sdowdy@charon.unm.edu (Stephen Dowdy) (12/23/87)

In article <3778@blia.BLI.COM> ted@blia.BLI.COM (Ted Marshall) writes:
>In article <2080@charon.unm.edu>, sdowdy@charon.unm.edu (Stephen Dowdy) writes:
>> the vt100 gets extremely confused about what its
>> scrolling region is and where to put the next line of text.  This
>> problem persists even upon exiting TPU.
>
>As I recall, there was a firmware bug in at least some VT-100's. I think it
>had to do with scrolling regions under soft-scroll. I remember that it could
>be pushed far enough that the terminal did a full reset.
>I don't know if this was fixed in later versions of the VT-100 family (I assume
>so) or what models/serial-numbers had the problem. However, I do remember that
>turning off soft-scroll mode fixed it. Try that.
>
>Ted Marshall       ...!ucbvax!mtxinu!blia!ted <or> mtxinu!blia!ted@Berkeley.EDU

Thanks for the info.
I originally had a header window of 1 line at the top, and a text display
window from line 2 to the second to last line, and a prompt/message area
at the bottom.  I removed the header window from the top line
of the screen, and let the main window go from line 1 to the second to last
line and put my header info in the status line.  I would rather have had
the header window there with the application title, but i needed this to
work on all terminals that would be used.  Oh Well.  Anyway, this setup
has remedied the problem.

Exactly what are you referring to when you say "soft-scroll"?  I'm not
aware of a distinction of soft or hard or no scroll for the vt100 series.

--stephen
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ted@blia.BLI.COM (Ted Marshall) (12/26/87)

In article <2109@charon.unm.edu>, sdowdy@charon.unm.edu (Stephen Dowdy) writes:
> Exactly what are you referring to when you say "soft-scroll"?  I'm not
> aware of a distinction of soft or hard or no scroll for the vt100 series.

The DEC VT-100, 200 and 300 families all have two user-selectable scrolling
modes, jump and soft scroll. Jump scroll is the "traditional" CRT scrolling
mode: when the terminal receives the LF, it immediately moves the text on the
screen up on character line. Soft scroll causes the terminal to smoothly
scroll the new line onto the screen, one raster line at a time, at a fairly
slow rate (it uses flow control to slow the output from the CPU, if necessary).
The effect, when the CPU is steadily sending text, is that the screen slowly
and smoothly scrolls up the text, like the credits at the end of many movies.

The two modes are selectable from Set-Up. I don't remember how VT-100 set-up
works so I can't give you specifics.

P.S. Merry Christmas, everyone.

-- 
Ted Marshall       ...!ucbvax!mtxinu!blia!ted <or> mtxinu!blia!ted@Berkeley.EDU
Britton Lee, Inc., 14600 Winchester Blvd, Los Gatos, Ca 95030     (408)378-7000
The opinions expressed above are those of the poster and not his employer.