AN2335 datasheet(33/40 Pages) STMICROELECTRONICS

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AN2335

Application Information

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9.4

Interrupt generation description

The LIS302DL provide two fully-programmable interrupt sources which may be configured

to trigger different inertial events. Among them it is worth mentioning the recognition of Free-

Fall and Wake-Up events. Whenever an interrupt condition is verified the interrupt signal is

asserted and reading either the FF_WU_SRC_1 or FF_WU_SRC_2 registers it is possible

to understand which condition has occurred.

The block diagram of the interrupt block is given in the pictures below.

Figure 13.

Interrupt Generation Block Diagram

Figure 14.

Free-Fall, Wake-Up Interrupt Generator

FF or WU interrupt generation is selected for each interrupt generation channel through AOI

bit in the corresponding FF_WU_CFG register. If AOI bit is ‘0’ signals coming from

comparators are put in logical or. Depending on values written in FF_WU_CFG_1 and

FF_WU_CFG_2 registers every time the value of at least one of the enabled axes exceeds

the threshold written in module in the corresponding FF_WU_THS_1 and FF_WU_THS_2

registers a FF, WU interrupt is generated. Otherwise if AOI bit is ‘1’ signals coming from

comparators are going into a “NAND” port. In this case an interrupt signal is generated

whenever the acceleration signal of all the enabled axes is below the threshold written in

FF_WU_THS_1 or FF_WU_THS_2 registers.

Ph_Gen

Ctrl_reg1(DR,PD)

100/400Hz

ADC

HP filter

Output Reg

FF_WU2

FF_WU1

SRC1

SRC2

Serial

Interface

(SPI

& I2C)

CFG 1

CFG 2

Ctrl_reg2(FDS)

Ctrl_reg2(HP FF_WU1)

Ctrl_reg2(HP FF_WU2)

THS reg

|b|>a?

Accel_X

Accel_Y

Accel_Z

X_en

Y_en

Z_en

FF_WU_CFG(AOI)

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