DIGILENT PmodACL2 3-Axis MEMS Accelerometer Owner’s Manual

: June 12, 2024
: DIGILENT

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DIGILENT PmodACL2 3-Axis MEMS Accelerometer

PmodACL2TM Reference Manual

Revised May 24, 2016
This manual applies to the PmodACL2 rev. A 1300 Henley Court Pullman, WA 99163 509.334.6306

www.digilentinc.com

Overview
The PmodACL2 is a 3-axis MEMS accelerometer powered by the Analog Devices ADXL362. By communicating with the chip via the SPI protocol, users may receive up to 12 bits of resolution for each axis of acceleration. Additionally, this module offers external trigger sensing through single or double-tap detection as well as power saving features through its inactivity monitoring.

Product Features

3-axis MEMS accelerometer
Up to 12 bits of resolution per axis
User-selectable resolution
Activity/inactivity monitoring
Low current consumption

Product Usage Instructions

Connect the PmodACL2 to your microcontroller or development board using the SPI protocol.
Power on the PmodACL2 and your microcontroller/development board.
To read the acceleration data, send the appropriate commands to the PmodACL2 via SPI.
The PmodACL2 provides up to 12 bits of resolution for each axis of acceleration. Use the user-selectable resolution feature to configure the desired resolution.
To detect external triggers, enable the single or double-tap detection feature on the PmodACL2.
To save power, utilize the inactivity monitoring feature of the PmodACL2.
Refer to the PmodACL2 Reference Manual for detailed information on the SPI commands and configuration options.

Overview
The PmodACL2 is a 3-axis MEMS accelerometer powered by the Analog Devices ADXL362. By communicating with the chip via the SPI protocol, users may receive up to 12 bits of resolution for each axis of acceleration. Additionally, this module offers external trigger sensing through single or double-tap detection as well as power saving features though its inactivity monitoring.

The PmodACL2.

Features include:

3-axis MEMS accelerometer
Up to 12 bits of resolution per axis
User-selectable resolution
Activity/inactivity monitoring
Low current consumption at <2 μA at 100Hz
Free-fall detection
Small PCB size for flexible designs 1.0 in ×
0.8 in (2.5 cm × 2.0 cm)
Follows Digilent Pmod Interface
Specification Type 2A
Library and example code available
in resource center

Functional Description
The PmodACL2 utilizes Analog Devices ADXL362 to provide MEMS acceleration data to the system board. With its deep 512-sample FIFO buffer, users are able to view a long string of events prior to a triggered interrupt or simply be able to have the system board access acceleration data when the user finds it most convenient.

Interfacing with the Pmod

The PmodACL2 communicates with the host board via the SPI protocol. To read from the on-board data registers,
the Chip Select line must first be pulled low and then send a command byte to read from the data registers (0x0B).
The desired address byte must be sent next, and then the desired byte is received with the MSB first on the falling clock edge. Because the address pointer auto-increments to the next address byte, it is possible to read multiple bytes consecutively by continuing to pulse the Serial Clock line. An example set of commands to read from the yaxis register is given below:

Command Read	First Y-axis Address
0	0
0	0

LSB Byte of Y-axis Data	MSB Byte of Y-axis Data
b7	b6
SX	SX

Note: Each SX bit is the same value as the most significant bit of the y-axis data.
To read from the FIFO buffer, a command byte to write to a data register (0x0A) must first be sent so that we can configure the FIFO Control register (address 0x28) to indicate that we want the FIFO buffer to store data. After the ADXL362 has been configured to use the FIFO buffer, a command byte to read from the FIFO buffer (0x0D) must first be sent, then followed by pairs of data bytes containing which axis is being measured as well as the acceleration data. An example set of commands to read from the FIFO buffer is given below:

Command Read FIFO Control Register Address Command FIFO Read
0 0 0 0 1 0 1 0 0 0 1 1 0 0 0 0 0 0 0 0 1 1 0 1

LSB Byte of Axis Data	MSB Byte of Axis Data
b7	b6
b15	b14

Note: Each SX bit is the same value as the most significant bit of the y-axis data. b15 and b14 represent which axis the incoming data represents.

Pinout Description Table

Pinout Table of the PmodACL2

Connector J1| | Connector J2|
Pin| Signal| Description| | Pin| Signal| Description| Pin| Signal| Description|
1| ~CS| Chip select| 7| INT2| Interrupt Two| 1| INT1| Interrupt One|
2| MOSI| Master Out Slave

In

| 8| INT1| Interrupt One| 2| G| Power Supply

Ground

|
3| MISO| Master In Slave

Out

| 9| NC| Not connected| Connector J3|
4| SCLK| Serial clock| 10| NC| Not connected| Pin| Signal| Description|
5| GND| Power supply

ground

| 11| GND| Power supply

ground

| 1| INT2| Interrupt Two|
6| VCC| Power supply

(3.3V)

| 12| VCC| Power supply

(3.3V)

| 2| G| Power Supply

Ground

|

The PmodACL2 also has two programmable interrupt pins available for use. Both of these pins can be set to trigger an interrupt upon multiple different triggers including activity/inactivity (to help reduce system power), when the FIFO buffer is filled to a desired level, when data is ready to be retrieved, and other triggers.
Any external power applied to the PmodACL2 must be within 1.6V and 3.5V. Consequently, with Digilent system boards, this Pmod must be run off of a 3.3V rail.

Physical Dimensions
The pins on the pin header are spaced 100 mil apart. The PCB is 0.95 inches long on the sides parallel to the pins on the pin header and 0.8 inches long on the sides perpendicular to the pin header.

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