Studio Technologies 92 - Manual (Page 17)

Model 92 User Guide Issue 1, December 2006
Studio Technologies, Inc. Page 17
operation, only experience can serve as the
best teacher. It’s recommended that some
“bench” experimentation be done prior to
going full bore out in the field.
Master/Slave Data Link
For two Model 92 units to be used in a
master/slave arrangement they must be
interconnected with a 2-conductor signal
path. This connection is referred to as the
master/slave data link. It supports the trans-
mission of bi-directional serial data as well
as linking the power supply common con-
nections of both units. A BNC connector
is used for the master/slave data link. This
type of connector was selected not because
of a specific technical requirement, but
because of its wide popularity in the broad-
cast and video industry. In many applica-
tions where DT12 cable assemblies are to
be tested there will also be BNC-terminated
video cables present. This will most likely
allow the easier method of interconnecting
two Model 92 units. However, there’s no
reason that other types of cable can’t be
used. Options can include shielded micro-
phone cable and twisted pair telephone
cable. While using coax will allow the great-
est distance between Model 92 units, even
twisted pair has been tested at over 4000
feet! This should be well in excess of the
length of any DT12 cable assembly that
needs to be tested.
It’s important to note that two metallic con-
nections must be made between the master
and slave Model 92 units. When using a
coaxial cable the two metallic connections
would consist of the inner conductor and
the shield. Alternately pins 2 and 3 of a
standard audio cable that uses XLR connec-
tors would serve the purpose. However, any
transformers, “baluns,” or capacitors in the
connection path that provide DC isolation
will prevent master/slave operation.
After interconnecting two Model 92 units, it’s
quite easy to confirm that the master/slave
data link has been established. Temporarily
designate one of the units as slave. Be sure
that it is powered down. Turn on the other
(master) unit by tapping its power button.
Then press and hold its power button until
the system mode has changed to master-
male active or master-female active. At this
point if the connection is valid data com-
ing from the master Model 92 will “wake
up” the slave unit. The active LED, located
below the BNC connector, on each unit will
flash as data packets move between the
units. Once data link operation has been
confirmed power down the unit designed
as master. The slave unit should also power
down in response to a command from the
master unit.
Note that maintaining a short circuit on
the Model 92’s data link BNC connector
is something to avoid. Due to an idiosyncra-
sy in the operation of the data communica-
tions transceiver integrated circuit an error
in the data link wiring can force the Model
92 to stay in the powered up state. The
10-minute inactivity timer will not be able to
power down the unit; nor will a low-battery-
voltage condition be able to invoke a power
down either. Damage to the battery will
occur if a deep discharge state is reached.
This situation is not something that the
Model 92’s designers are especially proud
of, but they weren’t aware of the condition
until it was too late to make a change. And
contacting the world-class maker of the inte-
grated circuit didn’t get much of a response
except “hmmm…” So in conclusion, as long
as the BNC connector isn’t presented with a
short circuit or a low impedance load condi-
tion things will work fine.