Crown Audio IQ-SLM8 - Manual (Page 20)

Page 20
IQ–SLM-8 System and Load Monitoring IQ System Component
Reference Manual
5.4 Crown Bus I/O
The Crown Bus loop input is received by an opto-
isolated 20 mA current loop to TTL receiver. The output
of the receiver is connected to a UART within the
microprocessor which qualifies incoming messages. If
an incoming message is determined to be for the
SLM-
8, appropriate action and response is calculated and
sent out the Crown Bus loop output via a Crown Bus
output driver circuit.
Note: The Crown Bus loop input is
logically or’d with the output. This connection allows
any signal at the receiver to be transmitted through the
SLM-8 and out of the Crown Bus loop output. Bypass
relays short the Crown Bus input to output terminals if
AC power is removed from the
SLM-8. This ensures
communication through the loop even if the SLM-8 is
not connected to AC power.
The AUX input is monitored by the microprocessor.
The input is protected by overvoltage diodes and has
an input impedance of 10 kohms.
The AUX output is controlled by the microprocessor.
The output is an open collector with a 1 kohm series
resistor for current limit. Max voltage out is +15 VDC.
Max current out is 15 mA.
The IQ device address is set by an eight position DIP
switch which is monitored by the microprocessor. In-
coming messages are compared to the switch setting
for qualification that the message is for the specific
SLM-8 and not for some other device on the loop.
5.5 Microprocessor and Memory
The 6811 microprocessor is the central controller for
the
SLM-8. It uses internal and external memory re-
sources for program and data operations. It performs
all IQ communication as well as data acquisition calcu-
lations. It also controls the test signal generator and
loudspeaker monitor relays. Internal memory is 32 K x
8 EEPROM for memory backup, 8 K x SRAM for run-
time parameter storage.
5.6 Power Supplies
Unregulated power is supplied by the power trans-
former. The power transformer can be wired in series
or parallel for 120/240 VAC operation. The unregulated
power is regulated by five separate voltage regulators.
Power for analog circuity is via linear ±15 VDC and ±5
VDC regulators. The digital circuitry is powered by a
monolithic switching regulator at +5 VDC.
5 Technical Information
The SLM–8 provides accurate testing and recording of
two critical system parameters: impedance and fre-
quency response. See Sections 1 and 2 for a list of
features and facilities. Figure 5.1 shows the block dia-
gram of the unit.
5.1 Load Monitor Data Acquisition
The Load Monitor inputs are connected to current and
voltage sensing circuitry. Current sensing is performed
by an isolated, wide bandwidth, toroidal wound current
transformer. The output of the transformer is amplified
and converted to the DC equivalent of RMS current
and then sent to the data acquisition multiplexer. Volt-
age sensing is performed by high input impedance,
balanced differential input amplifiers. The output of
each differential amplifier is converted to the DC
equivalent of an RMS voltage and sent to the data
acquisition multiplexer. The data acquisition multi-
plexer is controlled by a 6811 microprocessor to select
the channel for Analog to Digital conversion. The A-to-
D conversion is accomplished by an 18-bit integrating
ADC. The digital output of the ADC is sent to the
microprocessor for subsequent calculations. The mi-
croprocessor divides the voltage data by the current
data to calculate impedance for a given frequency.
This calculation is performed for each frequency of
interest.
5.2 Signal Generator
The required test signal is generated by a Direct Digital
Synthesis IC. The frequency of oscillation is controlled
by the microprocessor. The DDS output is sent through
a digitally controlled attenuator. The attenuator is also
controlled by the microprocessor. The output of the
attenuator is converted to a balanced signal by the
output line driver.
5.3 Loudspeaker Monitor
Each Load Monitor input is directly connected to a
relay. The relay output is connected to a fused “bus”
and made available at the back panel of the
SLM-8.
The relays are controlled by the microprocessor and
thus are available for user control via an
IQ System.
Any of the eight channels may be connected to the
output terminals for external remote loudspeaker
monitoring.