vt220 question

From: der Mouse <mouse_at_Rodents.Montreal.QC.CA>
Date: Tue May 4 23:28:52 2004

>> [...serial-line break condition...]
> A break consists of making the transmit data pin +ve for 200ms (or
> whatever).

"Or whatever". I've used baud rates for which 200ms is less than one
bit time (not often, and only for special purposes, but I've used 'em).
Of course, I've not used them for purposes for which break conditions
are very important. :)

> In fact the normal way to detect a break at the receiving end on a
> modern system is to look for a framing error detected by the UART
> chip -- this means the received character didn't have valid stop
> bits, which is the case for a true line break.

A few (better) serial-interface chips detect and report a break
condition as distinct from other framing errors. (Some of them
consider "break" as a subclass of "framing error" - I mean that they
allow the host to tell the difference between a break and a non-break
framing error.)

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Received on Tue May 04 2004 - 23:28:52 BST