chris@yarra.oz.au (Chris Jankowski) (11/20/89)
Can somebody explain what is break condition and where is it
defined ie. in what standard?
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.
This however contradicts 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?
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.roe@sobmips.UUCP (r.peterson) (11/21/89)
From article <5464@yarra.oz.au>, by chris@yarra.oz.au (Chris Jankowski): > Can somebody explain what is break condition and where is it > defined ie. in what standard? > The RS-232 "standard" :-). > 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 (?)). The TRANSMIT DATA line is held in a continuous SPACE condition for at least .25 seconds (longer than a start bit at any baud rate). This is transmitted to the remote modem which (configuration depending) should duplicate the break at its' TD line. > [...] > This however contradicts 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? > A character framing error occurs when a start bit is seen with no stop bit at the proper time. A break satisfies this condition, and, since what is being transmitted is a continuous SPACE, all 'data bits' are interpreted as zeroes. -- If the brain were so simple we understood it|Roe Peterson We would be so simple we couldn't. |{attcan,mcgill-vision}!sobeco!roe
doug@letni.UUCP (Doug Davis) (11/22/89)
In article <5464@yarra.oz.au> chris@yarra.oz.au (Chris Jankowski) writes: >Can somebody explain what is break condition and where is it >defined ie. in what standard? Uh, well, like, perhaps the RS232-C standard?? >Just to start things off I will give you my intuitive understanding: I don't mean to pick nits, but you don't understand.. ;-) >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 (?)). Welllllll,, the transmit data line goes to a space condition. Zero volts for 23-27ms. Normally the transmit data line is at -12VDC in relationship to ground on pin 1 (frame ground) or 7 (signal ground) depending on the device. >A modem if present should detect this condition and pass it to >the remote modem (by stopping to issue carrier (?) for how long (?)). Uh, assuming the modem is set up properly it should send spaces for the amount of time the TD line is at zero. Otherwise some modems go into command mode. Others just freak out and die. >The remote modem then should pass this condition by dropping >voltage on one of its RS232C lines - again which (?) and for how long(?). Again this has to be set up to do this. some modems will eat incoming long spaces.. (which is what that is called) others will disconnect and some, again, will freak out die. >This in turn may trigger some action in the receiving computer. This also assumes that the receiveing computer can detect such a condition. mostly they interpret the existance of a long space to be a frame error, (the absence of stop bits) and the software in the computer has to deal with that it's own. >This however contradicts what my termio(7-att) manual page says: >....the break condition (a character framing error with data all zeros)... Your att manual is correct. A space is a zero, and 23-27ms of them will almost always be a frame error at any baud rate. >What is character framing error then? THe absents of one or more stop bits in a string of spaces.. __ Doug Davis/1030 Pleasant Valley Lane/Arlington/Texas/76015/817-467-3740 {texsun, motown!sys1, uiucuxc!sys1 lawnet, attctc, texbell} letni!doug "Act first, solve problem, appologize for the mess later."
flinton@eagle.wesleyan.edu (11/22/89)
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 <Break> 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 <ctrl-@>, 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 <Break> and <Ctrl-@><Ctrl-@><Ctrl-@>...<Ctrl-@> 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.
dave@stcns3.stc.oz.AU (Dave Horsfall) (11/28/89)
In article <2221@stcns3.stc.oz.AU>, I wrote: | Depending on whether your vendor implements "true" RS-232C, it goes to | a MARK condition (-ve voltage or 0 volts) for that time. Etc. That of course should read "SPACE", not "MARK". That's what I get when I'm in a hurry to go home... Sorry 'bout that. -- Dave Horsfall (VK2KFU), Alcatel STC Australia, dave@stcns3.stc.oz.AU dave%stcns3.stc.oz.AU@uunet.UU.NET, ...munnari!stcns3.stc.oz.AU!dave