Station Control Modules
68P81096E32-E
7
08/06/07
A BNC connector (located on the front of the CLN1465) is provided to allow the
highly-stable external 5 /10 MHz source to be input to the OSC
IN
input of the PLL
to perform frequency netting. Refer to the Routine Maintenance section in this
manual for recommended intervals and procedures for netting the station refer-
ence.
The Station Reference Circuitry may operate in one of three modes:
•
Normal Mode – In this mode, the control voltage is turned off (via control
voltage enable switch) and the high-stability VCO operates in an open loop
mode; stability of the VCO in this mode is 2 PPM per year.
•
Manual Netting Mode – Periodically, an external 5 / 10 MHz source is re-
quired to fine tune, or “net”, the 16.8 MHz reference signal. In this mode,
the PLL compares the 5/10 MHz reference and a sample of the 16.8 MHz
VCO output and generates up/down pulses. The Host
μ
P reads the pulses
(via SPI bus) and sends correction signals (via SPI bus) to the VCO to adjust
the output frequency to 16.8 Mhz
±
0.3 ppm.
•
High-Stability Mode – For some systems, the free-running stability of the
VCO is unacceptable for optimum system performance. Therefore, an exter-
nal 5/10 MHz source is connected permanently to the BNC connector. In
this mode, the PLL compares the 5/10 MHz reference and a sample of the
16.8 MHz VCO output and generates a dc correction voltage. The control
voltage enable switch is closed, allowing the control voltage from the PLL
to adjust the high-stability VCO frequency to 16.8 Mhz
±
0.3 ppm. The VCO
operates in this closed loop mode and is continually being frequency-con-
trolled by the control voltage from the PLL.
Digital Signal Processor (DSP) and DSP ASIC Circuitry
General
The second half of the MC68356 contains a 56002 Digital Signal Processor
(DSP). All station transmit and receive audio/data is processed by the DSP and
related circuitry. This circuitry includes the DSP, the DSP ASIC, and the Audio
Processing circuitry. All audio signals input to or output from the DSP ASIC are
in digitized format. The digitized audio is transfered to/from various codec ICs in
the Audio Processing circuitry along corresponding serial buses (dependent on the
particular routing of an audio signal).
Note
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