| Break is defined as dropping the transmit line (not DTR, though
DEC may play some games with that, though I would be surprised)
for 320 (?) milliseconds. This is far longer than any one character
would be, and is a special 'out of band' signalling method. If
you see what looks like a really long character of all zeros with
no stop bit where you expect it (some terminals will carve away
the first 8 bits of this and say "aha! a null!"), that's a break.
I gather it originally came from the fact that when a line would
come down (physically break) you could detect it this way (back
when terminals used current loops). There's also a 'long break'
that lasts for some 2 seconds (control-break on VT-100s) that can
be used for other things.
Willie
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| Technically, a break is at least one bit time longer than a complete
character for the baud rate you are using. Making it an arbitrary 320ms
is a quick and dirty way of accomplishing this. What happens is that
the input shift register (UART or software technique) does not see a
transition back to logical zero at the end of a character time. This
generates what is known as a framing error. Break will also drop DTR
on some terminals, but it's "true" definition is what I said above.
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