Path: utzoo!news-server.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!zaphod.mps.ohio-state.edu!mips!spool.mu.edu!snorkelwacker.mit.edu!thunder.mcrcim.mcgill.edu!mouse From: mouse@thunder.mcrcim.mcgill.edu (der Mouse) Newsgroups: comp.sys.next Subject: Re: How to generate BREAK code? Message-ID: <1991Mar10.115359.17943@thunder.mcrcim.mcgill.edu> Date: 10 Mar 91 11:53:59 GMT References: <846@lychee.cs.utexas.edu> <446@heaven.woodside.ca.us> Organization: McGill Research Centre for Intelligent Machines Lines: 33 In article , jbryans@beach.csulb.edu (Jack Bryans) writes: > In article <446@heaven.woodside.ca.us> glenn@heaven.woodside.ca.us (Glenn Reid) writes: >> [...stuff about break "characters"...] > ^@ is the null character. It's value is 0, regardless of radix :-). > A break isn't an ASCII character -- it's the absence of any signal on > the serial line for some period of time. Just to be picky, it's the *presence* of signal, not *absence* of signal. The absence of signal, corresponding to the SPACE condition of the line (not to be confused with the ' ' character), simply indicates an idle line. The SPACE->MARK transition indicates the beginning of the start bit; normally, this is followed by some number of bits (typically 8) and then the stop bit; just as the start bit always is one bit time in the MARK condition, the stop bit is always one bit time in the SPACE condition. If the line is found to be in the MARK condition during the stop bit's time slot, this is a framing error. A break condition simply consists of holding the line in the MARK state long enough to guarantee the generation of a framing error. (Hmmm. I hope I haven't got SPACE and MARK interchanged....) > Short & long breaks may be recognized & differentiated by some comms > equipment. Well yes, there's that too. In addition to the out-of-band information "framing error occurred", more information can be carried by the length of time the MARK signal persists. der Mouse old: mcgill-vision!mouse new: mouse@larry.mcrcim.mcgill.edu