vt220 question

From: dave04a_at_dunfield.com <(dave04a_at_dunfield.com)>
Date: Tue May 4 10:38:31 2004

>On my VT220, as connected to a VAXStation 3100, depressing the 'BREAK'
>key on the LK401 causes an immediate processor halt and the display of a
>monitor prompt... >>> . Since I have it hooked up using the RS232
>port, and since there is no such thing as a real interrupting 'break' in
>RS232 - it must be some other code... or, is it? The VT220 Programmer
>Pocket Guide just says that he first 5 top-row keys are "local function
>keys and do not generate codes."
> But it still doesn't tell me what the hardware does when pressing
>'BREAK'. IF no one knows, I'll have to get out the break-out box and
>see if I can trap it.

BREAK on typical RS-232 terminal simply sets the line to the SPACE condition
for a number of character intervals. This causes a framing error at the
receiver (no stop bit) and many system will time this and if it persists
long enough will interpret it as a system attention function.

Better terminals will generate a timed pulse when break is depressed, some
terminals simply send a space condition for as long as the key is held down.

Dave Dunfield

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Received on Tue May 04 2004 - 10:38:31 BST

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