The short form:
I have no problem setting the default for PDP11 TTO to 7B instead of 7P,
although I'm sure some old software will break. If this is done, though,
I would suggest reverting the previous change to the printable character
mask back to its original settings. The pdp11_dc.c default settings
should also be set to 7B, because those always go through a TELNET session.
The long form:
In the beginning, SimH only ran on VMS and Unix, both of which had
excellent VT100-emulating terminal windows. At that time, all terminal
IO was full 8b, with no masking. Things fell apart with the advent of
the Windows port.
To begin with, Windows interpreted characters 128-255 as unique, and not
as variants of 0-127. So to get sensible output from systems that
thought they were implementing KSR-33s (bit<7> forced to 1), there had
to be a capability to mask to 7b. However, people ALSO used the terminal
to talk to Kermit, so 8b capability was needed. This led to the
introduction of general 7b/8b formatting.
There still were problems. Non-printing characters inserted into the
output stream put utter crap in the Windows terminal window. That led to
the creation of the 7P variant. This was done for the PDP11, in
particular, because its early software tended to do fills for the early
DEC terminals by outputting nulls, which Windows obligingly displayed as
garbage. I can no longer pinpoint the software that caused problems,
though, so I'm more than willing to let the user community rediscover
the issues.
It's important to remember that the PDP11 was introduced in 1970, with a
Teletype as its standard terminal. The LA30 and VT50 (of late unlamented
memory) weren't introduced until later, and the really useful terminals,
the LA36 and VT100, later still.
Finally, the Windows console window was always intended to emulate a
hard copy terminal. On a multiuser PDP11 system, the console was usually
a hard copy device, for logging. So the effort to do a VT100 emulator
INSIDE the simulator seemed pointless, particularly because the console
can be redirected to a TELNET application with a full VT100 emulator.
/Bob
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