[Simh] DosBox Break - was Re: HP Terminal emulators, ...

[Rodney Brown]

On 13/04/16 23:34, Clem Cole wrote:
>
> On Tue, Apr 12, 2016 at 11:14 PM, Tom Morris <tfmorris at gmail.com 
> <mailto:tfmorris at gmail.com>> wrote:
>
>     On Wed, Apr 13, 2016 at 12:28 AM, Clem Cole <clemc at ccc.com
>     <mailto:clemc at ccc.com>> wrote:
>
>
>         ​ Hang on -- BREAK is not in the old USASCII ​7 bit map.   As
>         explained in RFC 854, it was a >>key<< on the old Teletype
>         ASR33 (and the ATTEN key on the IBM 2741).   What BREAK did
>         was sent a very long (i.e. 1 second if I remember correctly)
>         "marking" time signal.
>
> ​Bad wording -- sorry see below...​
I don't remember using an Asynch terminal without a Break key, though my 
Hitachi Peach lacked one, despite the terminal emulator as  ROM Basic 
statement.
HP 3000 programs that didn't trim trailing blanks in output lines were 
reviled over a 300 baud acoustic coupler.

Reading the MSKermit source and the DOS Encyclopedia, Kermit sends 
either a 275 ms break or a 1.8 s long break.
This is done by turning on the BREAK state (SETBRK) in the 8250 Line 
Control Register, pausing for the period and
turning it back off again. I'd expect other terminal emulators to be 
doing something similar.

Reading the DosBox code, the NullModem serial case isn't checking for a 
Telnet connection, instead doing
I don't
nullmodem.cpp:/* setBreak(val) switches break on or 
off                                   **/
nullmodem.cpp-/*****************************************************************************/
nullmodem.cpp-
nullmodem.cpp:void CNullModem::setBreak (bool /*value*/) {
nullmodem.cpp-    CNullModem::setRTSDTR(getRTS(), getDTR());
nullmodem.cpp-}

So it should be easy to just send the Telnet break command when Break is 
turned on when telnet connected.
If so DosBox could be useful for running terminal emulators for SIMH.

>     Definitely not an ASCII character,
>
> ​That was my point.... I'm glad you agree.​
>
>
>     but where would an ancient electromechanical device like the
>     ASR-33 have kept this fancy 1 second timing logic?
>
> ​That's non-sense.   Timing on electromechanical devices was gears, 
> cams et al.   The teletypes had plenty of them.​   How BREAK was 
> implemented on the terminal is not relevant to the conversation, but 
> >>what<< is being sent its and how to do same function with todays tools.
>
>
>     I'm pretty sure that the length of the break is whatever length
>     you could be bothered to hold the key (and thus the line) down.
>
> ​I dp believe​ you are correct on this.  I'd have to go find the old 
> documents, but BREAK was defined in one of the communications 
> standards.  IIRC correctly it is as N character times of marking time. 
>   Where N was defined as a large number - in order of seconds not 
> small sub-seconds.
>
> Again if I recall correctly, BREAK is an concept that came from the 
> morse code world and was  inherited as transmission standards changed 
> over the next 100 yrs.
>
>     It was only in much later models of terminals that logic got
>     introduced between the BREAK key and the line.
>
> I'll take you word on it and I do believe you are correct, I've 
> forgotten and no longer have access to service manuals in my own 
> archives.​
>
> But it goes back to my point about what was being generated then, how 
> to generate it today.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.trailing-edge.com/pipermail/simh/attachments/20160414/fd6cb579/attachment.html>