Chapter 1. System Overview and Modes of Operation
21
CCU Circuit Description
The following section lists and describes the various components comprising the Common
Control Unit (CCU).
Microcontroller
The microcontroller, running a real time multi-tasking operating system, controls all the
functions of the CCU, provides alarm integration, accepts user commands over either the
asynchronous terminal or network interface, and issues commands to other provisionable
units over the RS-485 provisioning bus.
RS-485 Provisioning Bus Interface
Communication between the common equipment and channel cards takes place over a
balanced serial bus at 19.2 Kbps. This polled multidrop system allows only one unit to
transmit over the bus at any time. All equipment may monitor and receive messages
simultaneously.
RS-232C Interface
The RS-232C electrical interface provides the communications to the system control
terminal. The serial interface supports the following standard asynchronous
communication data rates: 300, 1200, 2400, 4800, 9600, and 19,200 bps. The default
setting from the factory is 1200 bps.
ROM
The Read Only Memory (ROM) contains the instructions used by the microcontroller.
RAM
The microcontroller uses the Random Access Memory (RAM) for "scratch pad" memory.
Nonvolatile RAM
Onboard Nonvolatile Random Access Memory (NVRAM) provides nonvolatile storage of
map information and other critical data for configuring the system. All channel card
settings and parameters are also stored in NVRAM. A 7-year lithium battery included on
the card preserves the information stored in NVRAM when power to the card is removed.
Date and Time Clock
The date and time (real time) clock provides accurate time information (day, date, hour,
minute, second) used for shelf configuration and operation. The date and time clock is
also powered by the 7-year battery.
Alarm Relay Circuits
The alarm relay circuits operate the relay contacts that are normally open for the visual,
audible, and minor alarms.
Alarm Cut-Off and Bypass Switch Circuits
The Alarm Cut-Off (ACO) and Bypass (BYP) circuits can be activated from front panel
switches on the CCU, or through terminal control.
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