On 13/04/16 23:34, Clem Cole wrote:
On Tue, Apr 12, 2016 at 11:14 PM, Tom Morris <[email protected]
<mailto:[email protected]>> wrote:
On Wed, Apr 13, 2016 at 12:28 AM, Clem Cole <[email protected]
<mailto:[email protected]>> 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.
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