dz11 / eia h3006 information wanted

[Tim Mann]

We don't have any real documentation for the H3006 distribution panel
in our 750's (the panel with the 8 RS-232 connectors joining the DZ-11
to the outside world) either, but I have some scribbles from a DEC
field service guy.  Here is what the switches do (the scribble is in
square brackets).

1 [busy]	Controls whether the BUSY line (pin 25) is shorted to DTR.
2 [rts]		Controls whether the RTS line is shorted to DTR.
3 [rclk]	Unknown
4 [srdt]	Unknown.  Not sure I read the scrawl correctly.
5 [std]		Unknown.
6 [fgr]		Probably controls whether frame ground is brought to pin 1.
7 		)
8		)-- 7-10 probably don't do anything.
9		)
10		)

Switches 1 and 2 on the distribution panel simply control whether the
BUSY and RTS outputs receive the same signal as DTR, or remain open.
Usually this is of no importance.  Some modems require RTS to operate.
You might as well run with 1-6 turned on and 7-10 off, which is what we
do.  Basically the switches don't make a heck of a lot of difference.

Background:
The DZ-11 provides RS-232 DTE (data terminal equipment) ports, which
are suitable for connection to DCEs (data communication equipment,
i.e., modems) with a straight cable.  This means the DZ ports transmit
data on pin 2 and receive it on pin 3, just like a standard terminal.
They also provide DTR as an output and CD (carrier detect) and RI (ring
indicator) as inputs.

If you need to hook up a hardwired terminal, the usual procedure is to
build yourself a "null modem" cable.  This is basically a cable with
pin 2 at one end connected to pin 3 at the other, and vice versa, plus
pin 7 (signal ground) connected straight through.  Some elaboration is
needed for devices that care about the various handshaking signals.
For instance, on a Unix system you may need to jumper the CD pin at the
DZ end of your cable to something so that Unix doesn't think you have
"hung up the phone."  You can either jumper it to the DZ's DTR output,
which your driver probably programs to always be TRUE, or to the DTR
output from the terminal.  The latter allows you to detect when the
terminal has been shut off or unplugged and treat that as a hang-up --
that is, if your terminal provides DTR as an output!  (Not all do.)
An alternative on some versions of Unix (maybe only 4.2BSD?) is to set
some system-configuration-time flags on the DZ driver that simulate
carrier being on all the time.

	--Tim