User's Manual

14 68P80801E35-B 5/1/2002
Base Radio Controllers EBTS System Manual - Vol 2
Enhanced Base Radio Controller
voltage to the VCO through an analog gate. The analog gate closes when three
conditions coexist: (1) The 5 MHz tests stable. (2) The PLL IC is programmed. (3)
Two PLL oscillator and reference signal output alignments occur.
A loss in the 5MHz / 1PPS signal causes the control voltage enable switch to
open. This complex PLL control allows the BR to maintain 16.5 MHz capability
during short disconnects (of approximately one minute) of the 5 MHz / 1 PPS
signal. (For example, during 5 MHz / 1 PPS cable maintenance work.)
When the gate enables, the control voltage from the PLL can adjust the
high-stability VCXO frequency. The adjustment can achieve a stability nearly
equivalent to that of the external, 5 MHz frequency reference.
The correction voltage from the PLL continuously adjusts the VXCO frequency.
The VXCO outputs a 16.8 MHz clock signal. The circuit applies this clock signal to
the receiver, and TISIC.
The TISIC divides the 16.8 MHz signal by seven, and outputs a 2.1 MHz signal.
This output signal then becomes the 2.1 MHz reference for the Exciter and
Receiver(s).
Input Ports
One general-purpose input register provides for EBRC and station circuit input
signals. The register has 16 input ports. The Host Data Bus conveys input register
data to the Host Microprocessor. Typical inputs include 16.8 Station Reference
Circuitry status outputs and reset status outputs.
Output Ports
Two general-purpose output registers distribute control signals from the Host
Microprocessor to the BRC and station circuitry. One register has 32 output ports
and the other register has 8 output ports. Control signal distribution occurs over
the backplane. The Host Data Bus drives the output ports’ latched outputs.
Typical control signals include front-panel LED signals and SPI peripheral enable
and address lines.
Remote Station Shutdown
The EBRC contains power supply shutdown circuitry. This circuitry can send a
shutdown pulse to the Base Radio Power Supply. BRC software generates the
shutdown control pulse.
After receiving a shutdown pulse, the power supply turns off BR power. Shut
down power sources include 3.3, 5.1, 28.6 and 14.2 Vdc sources throughout the
BR. Due to charges retained by BR storage elements, power supply voltages may
not reach zero. The shutdown only assures that the host processor enters a
power-on-reset state.
A remote site uses the shutdown function to perform a hard reset of all BR
modules.