Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site abnji.UUCP Path: utzoo!watmath!clyde!burl!ulysses!allegra!bellcore!decvax!harpo!whuxlm!spuxll!abnji!jeff From: jeff@abnji.UUCP (jeff) Newsgroups: net.micro.cpm Subject: re: need a break key Message-ID: <182@abnji.UUCP> Date: Wed, 16-Jan-85 12:47:12 EST Article-I.D.: abnji.182 Posted: Wed Jan 16 12:47:12 1985 Date-Received: Fri, 18-Jan-85 02:17:30 EST Organization: ATTIS, NJ Lines: 46 [I'm new to USENET,so please be kind] Causing a BREAK without a break key is tricky since BREAK is not a character but a line condition. An active RS232 line (transmit or receive data) is normally in the MARKING state (quiescent state) (binary 1, voltage between -3 and -25 volts). When a character is sent, the line sends a start bit (goes SPACE, binary 0, voltage between +3 and +25 volts), then the data bits (and parity if enabled), then a stop bit (back to MARKING). A framing error is caused when the end bit isn't received when it is expected, usually suggesting mismatched speeds. A break condition is when the line is put in the SPACE state for the time it takes to transmit a character (including start and stop bits) and thus cannot be confused with a character transmission. Some serial communication chips will detect the start and end of a break (since it may last a looooong time) and interrupt on both. Others just give a framing error with 00h data. The UNIX Administrator's Manual under TERMIO(7) under IGNBRK states that a break condition is a framing error with data 00h. Non-null data causing a framing error is considered a framing error. A break key causes the line to go spacing for about 1.1 to 2x a character time length (usually a long time - around 200 milliseconds). Your trick of going to a slower speed may work if the software treats framing error as a break (regardless if the data is 00h or not). If they are treated differently, then you must transmit a NULL character, usually control @. This will be undistinguishable from a break to all but the fussiest of receivers. This also points out that a framing error on a null character will be misinterpreted as a break. I trust this definitively answers your question. Ask anything more technical and I will refer to the EIA Standard for RS-232-C "Interface Between Data Terminal Equipment and Data Communication Equipment Employing Serial Binary Data Interchange". So there! +-----------------------------------------------+ | Jeff 'oh my gawd - it's one of THOSE!' Skot | | at beautiful downtown Somerset NJ | | AT&T Info Systems | | ..!abnji!jeff | +-----------------------------------------------+