RE46C190 datasheet(14/42 Pages) MICROCHIP

14 / 42 page

RE46C190

DS22271A-page 14

 2010 Microchip Technology Inc.

3.5

Interconnect Operation

The bidirectional IO pin allows the interconnection of

multiple detectors. In a Local Alarm condition, this pin

is driven high (High Boost) immediately through a

constant current source. Shorting this output to ground

will not cause excessive current. The IO is ignored as

input during a Local Alarm.

The IO pin also has an NMOS discharge device that is

active for 1.3 seconds after the conclusion of any type

of Local Alarm. This device helps to quickly discharge

any capacitance associated with the interconnect line.

If a remote, active high signal is detected, the device

goes into Remote Alarm and the horn will be active.

RLED will be off, indicating a Remote Alarm condition.

Internal protection circuitry allows the signaling unit to

have a higher supply voltage than the signaled unit,

without excessive current draw.

The interconnect input has a 336 ms nominal digital

filter. This allows the interconnection to other types of

alarms (carbon monoxide, for example) that may have

a pulsed interconnect signal.

3.6

Reduced Sensitivity Mode

A Reduced Sensitivity or Hush mode is initiated by

activating the TEST input (VIH). If the TEST input is

activated during a Local Alarm, the unit is immediately

reset out of the alarm condition, and the horn is

silenced. When the TEST input is deactivated (VIL), the

device enters into a 9-minute nominal Hush mode.

During this period, the HUSH integration limit is

selected. The hush gain is user programmable. In

Reduced Sensitivity mode, the RLED flashes for 10 ms

every 10 seconds to indicate that the mode is active.

As an option, the Hush mode will be cancelled if any of

the following conditions exist:

• Reduced sensitivity threshold is exceeded

(high smoke level)

• An interconnect alarm occurs

• TEST input is activated again

3.7

Local Alarm Memory

An Alarm Memory feature allows easy identification of

any unit that had previously been in a Local Alarm

condition. If a detector has entered a Local Alarm,

when it exits that Local Alarm, the Alarm Memory latch

is set. Initially the GLED can be used to visually identify

any unit that had previously been in a Local Alarm

condition. The GLED flashes three times spaced

1.3 seconds apart. This pattern will repeat every

43 seconds. The duration of the flash is 10 ms. In order

to preserve battery power, this visual indication will stop

after a period of 24 hours. The user will still be able to

identify a unit with an active alarm memory by pressing

the Push-to-Test button. When this button is active, the

horn will chirp for 10 ms every 250 ms.

If the Alarm Memory condition is set, then any time the

Push-to-Test button is pressed and released, the Alarm

Memory latch is reset.

The initial 24 hour visual indication is not displayed if a

low battery condition exists.

3.8

End of Life Indicator

As an option, after every 14 days of continuous

operation, the device will read a stored age count from

the EEPROM and increment this count. After 10 years

of powered operation, an audible warning will occur

indicating that the unit should be replaced. This

indicator will be similar to the chamber test failure

warning in that the horn will pulse on three times for

10 ms separated by 330 ms every 43 seconds. This

indicator will be separated from the low battery

indicator by approximately 20 seconds.

3.9

Photo Chamber Long Term Drift

Adjustment

As an option, the design includes a Long Term Drift

Adjustment for the photo chamber. If this option is

selected, during calibration a normal no-smoke

baseline integration measurement is made and stored

in EEPROM. During normal operation, a new baseline

is calculated by making 64 integration measurements

over a period of 8 hours. These measurements are

averaged and compared to the original baseline stored

during calibration to calculate the long term drift. All

four limits stored during calibration are adjusted by this

drift factor. Drift sampling is suspended during Hush,

Local Smoke and Remote Smoke conditions.

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