Studio Technologies 591 - Manual (Page 34)

Model 58/591 User Guide Issue 1, September 1999
Studio Technologies, Inc. Page 37
Appendix A
Controlling the Model 58
The Model 58 Central Controller uses
MIDI system-exclusive messages to con-
trol all functions. The Model 591 Control
Console is programmed to generate a
subset of what the Model 58 is capable
of doing. By using standard MIDI mes-
sages, the Model 58 can be used for a
wide range of special applications. Any
device that can be programmed to send
system-exclusive MIDI messages can be
used to control the Model 58.
While it is perfectly acceptable for devices
other than the Model 591 Control Console
to generate the MIDI system-exclusive
codes to “drive” the Model 58 Central
Controller units, a hardware detail must be
noted. The architecture of the Model 58
was created so that up to 8 units could be
connected together. A standard MIDI
hardware implementation would not allow
an output to drive this number of inputs.
To solve this problem the input impedance
of the Model 58’s MIDI input was raised
from the normal 220 ohms to 2000 ohms,
and, on the Model 591, a more sophisti-
cated output circuit was implemented.
The output circuit is essentially a current
source that can easily drive up to eight
of the modified inputs.
From our very limited tests, connecting
one or two Model 58 units to a standard
MIDI output works correctly. However,
connecting more than one or two will not
work reliably, or at all. Several solutions
to this problem are available. A custom
hardware implementation can duplicate
the Model 591’s output circuit, which
consists of a few low-cost components.
Alternately, the Model 58’s MIDI input
impedance can be changed to 220 ohms
by simply changing one resistor. This will
again limit the number of Model 58 units
that can be driven by a standard MIDI
output, but three or four should function
correctly. Schematic diagrams are avail-
able to purchasers of StudioComm sys-
tems. Contact the factory for details.
General Notes:
All MIDI messages to be acted upon are
system-exclusive type (F0H). No channel
mode, system common, or system real
time messages are utilized.
Studio Technologies, Inc. manufacturer’s
ID number is 00H 00H 56H
The Model 58’s product device ID number
is 03H.