Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!uwm.edu!rutgers!cmcl2!yale!eagle!flinton From: flinton@eagle.wesleyan.edu Newsgroups: comp.dcom.modems Subject: Re: break condition, framing errors Message-ID: <3921@eagle.wesleyan.edu> Date: 22 Nov 89 12:59:19 GMT References: <5464@yarra.oz.au> Lines: 57 In article <5464@yarra.oz.au>, chris@yarra.oz.au (Chris Jankowski) writes: > Can somebody explain what is break condition ... > ... what my termio(7-att) manual page says: > .....the break condition (a character framing error with data all zeros)... > ...What is character framing error then? In what follows, I may have committed the frequent sin of confusing 0 with 1 HI with LO up with down -- but systematically enough that I may not be as wrong as would appear on the surface. Anyway: Here's what I learned some years ago by just LISTENING at 300 baud: hitting the break key sends a string of "space" bits ("0" 's) that lasts half a second or so -- long enough that the "framing bit(s)" that should turn up as "1" 's after every 8 or so "data" bits are noticeably absent, causing recognition of a framing error. Remark: at 300 baud, which uses simple frequency shift keying, "mark" or "1" is signalled by one fixed audible frequency; "space" or "0" is signalled by a frequency approx. 225 Hz lower. Depending on whether you're in originate or answer mode, the frequency difference will be quite recognizable as either a "fat" minor third or a "slender" whole-tone, to use musician's terms. At the RS-232 port on your terminal, the data output pin (pin 2 usually, which usually connects to pin 2 on your modem, if you're using standard DB-25 connectors) is NEGATIVE for a "mark" bit and POSITIVE for a "space" bit; so drives it positive for a half-second or so, with no brief blips back to negative after every 8 or so 300ths of a second as would be the case with any "real" ascii character (the ascii character nearest a break is , in 8-bit, zero-parity form -- that's 9/300ths of a second of zeros -- a continuous sequence of which, however, is framed by start and stop bits at least one of which is a 1 -- the difference between and ... is quite audible (try listening! (-: ). Hope this helps. -- Fred [E.J. Linton, Wes. U. Math. Dept.] > > Just to start things off I will give you my intuitive understanding: > > When you press BREAK key on your terminal a voltage on one of the > RS232C control lines is dropped (which line (?) and for how long (?)). > A modem if present should detect this condition and pass it to > the remote modem (by stopping to issue carrier (?) for how long (?)). > The remote modem then should pass this condition by dropping > voltage on one of its RS232C lines - again which (?) and for how long(?). > This in turn may trigger some action in the receiving computer. > > > > Thanks for your help. > > -m------- Chris Jankowski - Senior Systems Engineer chris@yarra.oz{.au} > ---mmm----- Pyramid Technology Corporation Pty. Ltd. fax +61 3 820 0536 > -----mmmmm--- 11th Floor, 14 Queens Road tel. +61 3 820 0711 > -------mmmmmmm- Melbourne, Victoria, 3004 AUSTRALIA (03) 820 0711 > > ``If you're crossing the nation in a covered wagon, it's better to have four > strong oxen than 100 chickens. Chickens are OK but we can't make them work > together yet.'' - Ross Bott, Pyramid U.S., on multiprocessors at AUUGM '89.