VT100 Oddities

John ‘Sloppy’ Millington,

Don’t bother trying any of this on modern terminals or VT100 emulations. You need a real DEC VT100 for this.

Did you know that a DEC VT100 can be used as a musical instrument?

No? The DEC manuals didn’t mention that? Well, fortunately I’m still around to keep this obscure lore alive.

Go into SETUP-B and turn on keyclick.

Now send the following escape sequence to the VT100. You can either have a computer send it to the terminal, or you can directly enter it in local mode:

ESC[137q

You should be observing some very strange behavior at this point. The [q series of escape sequences are normally used for turning the keyboard LEDs on and off. But for some reason, this one turns on ludicrous repeat rate. That, combined with with keyclick, makes the VT100 emit a note when you hold down a key. And different keys (also in combination with the shift and caps-lock settings) make different notes.

With a little practice, you may be able to play your favorite song.

A bunch of ^Gs are NOT the most annoying sound a VT100 can make.

Nope, there’s one thing that’s worse. (As long as you don’t count the sound of someone trying to learn how to play The Number of the Beast using the trick mentioned above.)

Try this one:

ESC[145q

Oh god! Turn it off! Turn it off!!

Any other strange things a VT100 can do?

Sure! This one is actually documented, but fairly obscure:

ESC[2;9y

That was pretty lame. What else have you got?

Lame?!? Ok, I’ll show you! I saved the strangest for last!

This one isn’t quite as simple as the previous ones. You’ll actually have to know what you’re doing and have a little experience programming VT100s for this one.

Go to each of the lines on the screen, and make them double-width using the ESC#3, ESC#4, or ESC#6 sequences.

Set up a scrolling region using the ESC[r sequence. For example, ESC[5;15r should work.

Go to the bottom of the scrolling region and do a line feed. You might have to have a computer send this to the VT100 rather than enter it in local mode. (It’s been a while since I’ve done this.) If it doesn’t get funny right away, just keep sending line feeds.

Sometimes this just causes the terminal to reset. Other times, I’ve seen it do much stranger things, like display the same logical line on several different physical lines. The most impressive result is when you get an entire column of 24 cursors, flashing in unison.

Now go find the nearest tech support person and say “The computer said something about a virus, and then it did this.”