BL5980 Datasheet, PDF (21/30 Pages) SHANGHAI BELLING CO., LTD. – Low Voltage Photoelectric Smoke Detector ASIC

Figure 5-5: Timing Diagram for Mode T7
BL5980
5.5 LTD Baseline Measurement
If the Long Term Drift Adjustment is enabled, a Long Term Drift Baseline must be set. If an
accurate value is known based on previous chamber characterization, it can be loaded above in
T7 with the serial data. If not, zeros can be entered as placeholders in T7 and a long term drift
(LTD) baseline measurement must be made. To do this, the unit should be connected to its smoke
chamber and placed in a no-smoke condition. To enable the baseline measurement, pull TEST
from VSS to VBST again (or a total of 8 times) and return to VSS. Once the chamber is clear,
pulse FEED low to high to make the baseline measurement. The duration of this pulse should be
at least 2ms.
After baseline LTD measurement has been made, pulse IO with FEED held low to store the result
in memory.
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