ZDP323B Series Digital PIR Sensor

Product Specification

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PS041703-0324 - Preliminary

Page 9

9.5

Trigger Output Mode

The ZDP323B Digital PIR Sensor can operate in a Trigger Output Mode to signal a host

MCU when a motion event is detected. When Trigger Output Mode is enabled, the

SDA/TRIG pin is driven active low when the sensor signal meets the defined motion

detection qualification parameters.

9.5.1 Enabling and Disabling Trigger Output Mode

Trigger Output Mode is enabled by writing control register TRIGOM (Bit 23) to a 1 and is

disabled by writing it to a 0. The default state is disabled.

When enabled, the SDA/TRIG pin remains open drain (external pull up resistor required)

until a qualified motion event is detected. SDA/TRIG is driven low for 50µs when a motion

event is detected.

When Trigger Output mode is enabled, if the SCL pin is driven low while the SDA/TRIG pin

is active (low), and an I2C START condition is satisfied, the SDA/TRIG pin is released

automatically, and the sensor operates as slave. The ensures an I2C master can write to

and read from the device while Triggered Output Mode is enabled.

9.6

Detection Counter

This ZDP323B features a detection counter, which controls the Trigger Output. The

Detection counter is set to 1 when the signal output of the Bandpass Filter exceeds the

Detection Threshold level set in the Configuration Register (bits 15 to 22). If the next

bandpass filter output exceeds ½ the Detection Threshold, the counter is incremented to 2

and the Trigger Output is activated.

The Detection Counter is cleared under the following conditions:

• After activating the Trigger Output.

• When the bandpass filter output is less than ½ the Detection Threshold.

• When an I2C Start condition is satisfied.

Since the Detection Counter is reset on each I2C Start condition, the

Trigger Output will not be asserted if the I2C Master continuously

communicates with the device. If the I2C Master needs to continually

communicate with the device (monitoring Peak Hold data), Trigger Output

Mode should be disabled.

Note:

The bandpass filter sampling period is more frequent than the Trigger output update period

which can result in a situation where the Trigger Output deactivation appears delayed as

compared to the output data. This can result in the output data being up to +/- 3 counts

outside of the programmed threshold value.

Caution: