[Simh] VAX DZ terminal controller unit?

[Gary Lee Phillips]

OK, interesting. Here's what I learned by trying the "VH" device
(that's a DHV11, right?)

Though it is supposed to represent 8 lines, it created 16 terminal
devices in VMS. There are 8 TTnn devices and 8 TXnn devices. I believe
these are all programmed I/O, so the load on the processor increases
as it has to poll all those ports. There does seem to be a noticeable
slowdown in response.

However, with default terminal settings it does work much more
sensibly. Telnet to the designated port brings up a login prompt
immediately upon pressing ENTER. After a logout, the telnet session is
not disconnected unless you close the telnet application. However, you
can reuse that same telnet session without closing it, by just
pressing ENTER again to bring up a new login prompt. In other words,
the telnet client looks like a dedicated serial terminal and behaves
accordingly.

I see the VH device allows individual lines to be programmed as
"modem" and "disconnect" which probably means that if those options
are combined with SET TERM/MODEM on the VAX itself, the sessions will
actually disconnect on logout more like a normal telnet session. I'll
have to try that. The main drawback to VH is the fact that it creates
way more virtual terminals than I need and seems to have an impact on
VMS performance. As a workaround, though, it certainly is better than
the way DZ seems to operate at the moment.

--Gary