Crown Audio IQ-USM 810 - Manual (Page 34)

Page 34
IQ-USM 810 IQ Digital Processor / Digital Mixer
IQ-USM 810 Reference Manual
When wiring RJ-45 connectors, it is good practice to
follow the EIA/TIA 568B protocol for RJ-45 connector
cable. This protocol assigns wire colors as follows:
1 white-orange 5 white-blue
2 orange-white 6 green-white
3 white-green 7 white-brown
4 blue-white 8 brown-white
When attaching RJ-45 connectors to cable, be sure to
use the appropriate crimping tool and verify that the
connector is properly seated into the tool or damage
will result.
6.4 A Closer Look at IQ Bus Wiring
The IQ Bus is a serial communication loop designed to
transmit IQ commands and data. As implemented in
the IQ-USM 810, it is a 20-mA current loop operating at
a baud rate of 38.4 K.
The IQ Bus connection can use inexpensive twisted-
pair wiring (shielded or unshielded). The IQ Bus loop
must be unbroken. If fiber optic cabling is required,
contact the Crown Technical Support Group (see page
32 for contact information).
Here are some guidelines for twisted-pair wiring:
• When interference is a problem, use shielded
twisted-pair wire at least 26 AWG in size. The
wire should be of good quality and should have
low capacitance—30 pF/foot or less is suitable.
6.3 Working with RJ-45 Connectors
Pin numbers for standard RJ-45 connectors are indi-
cated in Figure 6.10.
Figure 6.10 RJ-45 Pin Numbers
The shield serves two purposes: First, it helps
prevent the IQ data signal from transmitting to
nearby audio wiring. Second, it helps prevent
outside RF from interfering with the data signal.
However, in most cases interference is not a
problem and, since unshielded wire has lower
capacitance, it is a better choice for typical appli-
cations.
• Minimize the total capacitance of a IQ Bus
loop. The total combined capacitance for an IQ
Bus loop should be less than 30 nF. To calculate
this, allow approximately 60 pF for each IQ com-
ponent in a loop. This accounts for a slight signal
degradation which occurs as data signals pass
through a component.
• Add an IQ Repeater for very long loops—
greater than 1,000 feet (305 m)—or when re-
quired by high-capacitance wire. Crown
recommends adding a repeater after 50 de-
vices or in the case of loops longer than 1,000
feet, although sometimes is possible to go
2,000 feet (610 m) or more before a repeater is
required. The most significant factor in deter-
mining maximum loop length is wire capaci-
tance. Lower capacitance will allow longer
loops (unsheilded wire usually has lower ca-
pacitance).
Outside RF interference is seldom a problem for a IQ
Bus loop—especially if shielded twisted-pair wire is
used. However, there are extreme situations when fiber
optic wiring is recommended. For example, locating a
IQ Bus loop next to an AM radio transmission line may
require fiber optic cabling. An extremely long IQ Bus
loop distance may also require fiber optic cabling.
6.5 The IQ-USM 810 as a 1-Loop IQ Interface
The IQ-USM 810 can serve as an IQ interface between
a host computer and a single IQ Bus loop for other
IQ
components. This can eliminate the need for an exter-
nal IQ Interface (
IQ INTII) in a small system. The IQ-
USM 810 connects directly to the host computer via
the DB9 serial connector. See Section 3.2 for specific
instructions on wiring and address settings.