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FUNCTIONAL DESCRIPTION
GENERAL OPERATION
The 7920SE
is a digitally synthesized
FM transceiver
that converts
conventional alarm system messages to radio messages, enabling an alarm
control panel, or controt/communicator, to communicate with the Central
Station via the radio security network Master Stations,
Once a radio
communications channel is programmed, the 7920SE automatically and
continuously fine tunes its frequency to that of the security network Master
Stations. This frequency is then stored in
EEPROM
and will be the initial
frequency of the 7920SE upon power-up and reset.
The 7920SE utitizes a No. 7625-3dB antenna which is an omni-directional
antenna, that may be mounted indoors, connected directly to the transceiver,
or may be mounted outdoors, using pre-assembled coaxial cable available
from Ademco. (Choice of cable lengths 5 feet, 12 feet; or 25 feet).
COMMUNICATION
The network communication scheme is based on a polling process, whereby
the network Master
Stations
regularly
poll each
of the
No.7920SE
Transceivers entered in the network database, and will alert the central station
if a particular Transceiver has not acknowledged repeated poll messages
within a Master Station programmable time period. This, in addition to the
Transceiver's "poll timeout" feature, which alerts the Master Station if it hae
not received a poll within a programmable
time period, provides full
Transceiver supervision. To further ensure that the Transceivers
are
periodically heard from, each Transceiver reguiarly transmits asynchronous
"I'm OK" messages to the Master Stations.
When the 7920SE receives an alarm from the alarm control panel (zone
trigger or serial data), it first waits a brief period of time (6-12 seconds) for a
network poll. If the 7920SE does not receive a poll within that time, it
transmits "alarm waiting" messages,
waiting a brief period
between
transmissions to receive network acknowledgment. When the transceiver is
polled, or the Master Station acknowledges the "alarm waiting" status of the
7920SE, the Master Station opens a time slot for the 7920SE to transmit the
actual alarm message. When the alarm message has been transmitted, it is
relayed through the Master Station network to the Central Station, where it is
processed by the No. 685 Digital Receiver. The 7920SE then reports the
alarm as a previously reported event in subsequent polls, for as long as the
alarm condition exists.
OLD ALARM TIMEOUT
The Transceiver will normally report all asynchronously transmitted alarms as
new events when it is eventually polled by the network. If desired, the
7920SE can be programmed to report the asynchronouslytransmitted alarm
as a previously reported event after a set time period (10 minutes -42 hours).
-5-
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