[Simh] Issues with VH simulation and 4.3BSD-Quasijarus

[dundas at caltech.edu]

> So ...If the DHV is supposed to the simh emulation of the combination of a
> DEC DH11 and DM11 pair (the DM11 was the modem control option for the DH),
> then this should "just work"

The SIMH VH device is a simulation of the DEC DHQ device (M3107), a dual
height Qbus board, normally supporting 8 lines and features DHU/DHV
"compatibility."  DHV was an earlier quad height incarnation, while the
DHU was a 16-line Unibus interface.  These are all similar to the historic
DH/DM combination but not identical.

It's been too long since I looked at the DH/DM combination but if I recall
correctly the actual programming was a bit different from the DHQ, though
the general idea was the same, similar to the Able device.

I have no experience with 4.3BSD-Quasijarus, so I couldn't say with any
authority whether or not it would support the DHQ, but as Mark indicated,
it would need to be set as a DHU for Unibus and 4.3 would likely need to
recognize the difference(s) between DHU and DH/DM.

Also agree with Clem's comment about DZ: a DZ could easily bring a 780 to
its knees with per character interrupts.  The Able board was historically
the first out of the gate, IIRC, to support reasonable serial performance
in the VAX arena.

John