Symmetricom 58502A - Manual (Page 76)

Chapter 5 Functional Description
Functional Block Description of the 58502A
5-4 User’s Guide
Controller Block
This block provides remote instrument management via commands
transferred through the RS-232 serial port. It also provides hardware
output alarm signals via the Alarm/Status connector that go active
when the controller block lights the front-panel system status alarm
indicator. Alarm inputs are received and processed by the controller
block.
The block consists of a microprocessor and associated support circuitry
that together facilitate control of all internal housekeeping, command
actions, diagnostic, and system status instrument functions. All
instrument functions are controlled and/or monitored by this block.
Panel LEDs Block
This block consists of hardware that provides visual indicators for the
operating status of instrument power, system alarm, inputs A and B,
and distribution amplifier channels 1 through 12. During normal
operation the power, all output status, and one or both input system
status indicators should illuminate.
If an effective input signal is lost (absent on both inputs A and B), then
both input A and B, and all output status indicators will be
extinguished, and the alarm indicator will be lit. If a hardware fault
occurs on one or more output distribution channels, then that channel's
associated indicator will be extinguished and the alarm indicator will
illuminate.
2-to-1 Switch Block
This block consists of inputs A and B routed to a programmable switch
that provides a single output to the input of the 1-to-12 Amplifiers and
Isolators block. Input selection switching for this block is controlled by
the input select line that arrives from the controller block.
The controller block input select line state (at power on from the
factory) selects input A over B, if valid signals are present at both
connectors, but will switch to input B automatically, if the signal at
input A fails. If input B fails and input A signal reappears, the
controller block will select input A again as the valid input signal
source. If both inputs fail, no select line state change will occur.