[Simh] PDP-11 DC-11 support

[Warren Toomey]

Göran I Åhling wrote:
> Great work done! And great spin-offs: I've been having problems to 
> understand 7b / UC settings for a while using a "plain -11"...
> Could these "diffs" and examples be made public to this list, somehow, 
> please?

Sorry for the delay, I was away over the weekend. My patch to pdp11_dl.c
is temporarily available here: http://minnie.tuhs.org/Z/simh/DL.diff.
Apart from the code to make the DL-11 act like a DC-11, the patch also
allows the device's address to be configured, and allows a carrier
detect flag to be set. Here are some example config lines:

set ttix address=17774000               ; Set the address to be a DC-11

	The default address, that of the DL, is 17776500.

set ttix carrier=dc                     ; Turn on the DC-11 carrier detect bit

	Other options are carrier=dl for the DL-11 carrier detect bit,
	carrier=off for no carrier detect bit enabled.

set ttox 7b                             ; Set output to be 7-bit, lowercase

	Other options appear to be "uc", "7p", and "8b".

The "show modifiers" command seems to show all the defined modifiers; it took
me a while to understand how to use the information it provided.

Cheers,
	Warren