Dsp Circuit; Power Supply - Orban OPTIMOD-FM 8500S Operating Manual

OPTIMOD-FM DIGITAL
ter displayed by the 8500S, because this meter indicates only the composite
signal generated by the DSP.
IC2B and IC3 together form a composite high-current buffer amplifier that re-
ceives the output of IC405A and drives the composite output connector J3
through RFI filter L3 and optional 75
The pilot reference D/A converter IC402 receives serial data from the DSP cir-
cuitry. After being buffered and low-pass filtered by IC407B, the resulting 19
kHz sine wave signal is passed to the Composite/SCA daughterboard and can
be connected to J2 through jumper J6.
The composite line driver amplifiers IC3 and IC4 are socketed in through-hole
packages to facilitate field replacement with simple tools. All other compo-
nents are surface-mounted and are not field-replaceable.

DSP Circuit

The DSP circuit consists of six Freescale dual-core 24-bit fixed-point DSP chips that
execute DSP software code to implement digital signal processing algorithms. The
chips operate at a core clock frequency of 245.76MHz.
The algorithms filter, compress, and limit the audio signal. A sampling rate of 64 kHz
and power-of-two multiples thereof, up to 512 kHz, is used. In stand-alone stereo
encoder mode, the minimum sample rate is 64 kHz.
System initialization normally occurs when power is first applied to the 8500S and
can occur abnormally if the 8500S's watchdog timer forces the SC520 to reboot.
Upon initialization, the SC520 CPU downloads the DSP executable code stored in the
flash memory. This typically takes about 7 seconds. Once a DSP chip begins executing
its program, execution is continuous. The SC520 provides the DSP program with pa-
rameter data (representing information like the settings of various processing con-
trols), and extracts the front panel metering data from the DSP chips.
During system initialization, the SC520 queries the DSP hardware about its opera-
tional status and will display an error message on-screen if the DSP fails to initialize
normally. Please note any such messages and be ready to report them to Orban Cus-
tomer Service.
The DSP chips are located on the I/O+DSP board — see the drawings starting on
page 6-35. IC1202 is a local voltage regulator on the DSP board that derives the
+1.2V core supply for the DSP chips from the +5V Power Supply.

Power Supply

Warning! Hazardous voltages are present in the power supply when it is connected
to the AC line. Several parts, including the heat sink, are hot to the AC power line.
Except for servicing, do not remove the insulating shield from the power supply.
Ω
build-out resistor R11.
6-13
TECHNICAL DATA