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  for   emergency   evacuation   signals.   The
continuous pattern is a 70% duty cycle continuous
pattern.
If a CO alarm is detected through the IO, the unit will
sound the CO tone pattern. The CO tone pattern con-
sists of 4 horn beeps in every 5.8s. Each horn beep is
100ms long and separated by 100ms.
3.10    Horn Synchronization
The horn synchronization function is programmable by
the user.
In an interconnected system, if one unit goes into Local
Alarm, other units will also go into Remote Alarm. The
IO line is driven high by the origination local smoke unit,
and stays high during the alarm.
If the Horn Synchronization function is enabled, at the
end of every temporal horn pattern and when the horn
is off, the origination unit will drive IO low, then high
again. This periodic IO pulsing high and low will cause
the remote smoke units to go into and out of the
Remote Alarm repeatedly. Each time a unit goes into a
Remote Alarm, its timing is reset. The horn sound of all
remote smoke units will be synchronized with the horn
sound of the origination unit.
A protection circuit ensures that the unit that goes first
into a Local Alarm will be the master unit that conducts
the horn synchronization. The units that go later into
Local Alarm will not drive the IO line. This prevents bus
contention problem.
This function works with the temporal tone pattern only.
3.11    Auto Alarm Locate
Auto Alarm Locate (AAL) is also a user-programmable
function. To use AAL, the horn synchronization has to
be selected first. The purpose of AAL is to let users
quickly find the local alarm units just by listening. The
local alarm units will sound the temporal pattern without
interruption. The remote alarm units will sound the pat-
tern with interruption. Every four temporal patterns
(or 16s), the remote units are kept silenced for one pat-
tern (or 4s).
The originating unit conducts the IO cycling. Every four
temporal patterns the IO is driven low for one temporal
pattern. In the remaining three temporal patterns, the
IO is still pulsing to keep the horn synchronized.
The RLED of the origination unit and other local smoke
units will be turned on 10 ms every 1s. The RLED of the
remote smoke units will be off.