[Simh] PDP-11 DC-11 support

[Warren Toomey]

Warren Toomey wrote:
>  Given that the unibus address can be reconfigured at run time, would
>  it be allowable instead to add a configuration command which would
>  let the user set the "carrier detect" bit?

On the assumption that this would be allowable, I have patched pdp11_dl.c
to be configurable at run-time to act as a DC-11, including the carrier 
detect flag in the CSR. The patch is here:

http://minnie.tuhs.org/Z/DL.diff

Here are the configuration changes:

set ttix address=17774000               ; Set the address to be a DC-11
					; (the DL address 17776500 is default)
set ttix carrier=dc                     ; Turn on the DC-11 carrier detect bit

Also allowable are:

set ttix carrier=off			; Disable setting of carrier detect bit
					; (off is the default setting)
set ttix carrier=dl			; Turn on the DL-11 carrier detect bit

and of course the unibus address of the device can be set to
any sensible value.

I hope this small patch can be included into the main tree, or if not, please
let me know how you would prefer to see it go.

Thanks,
	Warren