STMicroelectronics STEVAL-BCN002V1B User Manual

UM2501

User manual

How to use the BlueNRG-Tile Bluetooth LE enabled sensor node development kit

Introduction

The STEV board based on BlueNRG-2 SoC Bluetooth Low Energy application processor. This sensor board has accelerometer, gyroscope, magnetometer, pressure, humidity, Time-of-Flight and microphone sensors, and is powered by a common CR2032 coin battery.

The sensor board communicates with a Bluetooth LE enabled smartphone running the ST BLE Sensor app, available on Google Play and iTunes stores.

The STEVAL-BCN002V1D adapter board is used to program and debug the sensor board. The adapter board is powered via USB.

1. STEVAL-BCN002V1 “BlueTile” sensor node with inertial and environmental digital MEMS sensors, a digital MEMS microphone, a time-offlight proximity sensor and a Bluetooth 5.0 wireless system-on-chip with a Cortex-M0 core

2. STEVAL-BCN002V1D host board to Flash and debug the sensor node

AL-BCN002V1B Bluetooth LE enabled sensor node development kit features the STEVAL-BCN002V1 multi-sensor

Figure 1. STEVAL-BCN002V1B BlueTile kit

UM2501 - Rev 3 - June 2020

For further information contact your local STMicroelectronics sales of

fice.

www.st.com

1 Safety Information

Any type of usage not specified by the manufacturer may compromise the protection mechanisms in the device.

1.1 Class 1 laser product

VL53L1X contains a laser emitter; the device is designed to limit the laser output within Class 1 laser safety limits

under all conditions including single faults, in compliance with IEC 60825-1:2014 (third edition).

Recommended settings and operating conditions specified in VL53L1X datasheet and user manual MUST be respected.

The laser output MUST NOT be increased by any means and no optics should be to used focus the laser beam. Use of controls or adjustments or performance of procedures other than those specified in VL53L1X datasheet and user manual may result in hazardous radiation exposure.

UM2501

Safety Information

UM2501 - Rev 3

page 2/44

2 STEVAL-BCN002V1 BlueTile sensor node

I2C

LPS22HH

RGB LED

user button

UART

MP34DT05-A

LIS2MDL

32 MHz

I2C

VL53L1

400 kHz

1.6

I2C

Test points

TEST

VDDGND

MHz

RFTEST

PDM

inductor

10 pin

connector

32 KHz

Integrated

antenna

LSM6DSO

UART_RX line

I2C

BALF-NRG-02D3

HTS221

I2C

TEST ADC

ADC

RFTEST

SWD

SDASCL

IRQ

I2C

3 VO LTS

BlueNRG-2

Pi-network

BlueTile is a small form-factor reference design ready for you to extend and customize, as well as a development platform for BLE-enabled applications using the BlueNRG-2 and evaluate the performance of the sensors and the capabilities of the BLE.

Thanks to its small and thin design, BlueTile can be used in the field for data collection activities to test and develop new algorithms.

Figure 2. STEVAL-BCN002V1 BlueTile block diagram

BlueNRG-2: Bluetooth 5.0 network and application processor LSM6DSO: accelerometer and gyroscope LIS2MDL: magnetometer LPS22HH: barometer HTS221: relative humidity and temperature sensor VL53L1X: time-of-flight proximity sensor MP34DT05-A: microphone BALF-NRG-02D3: integrated balun

SDK. It is also an evaluation tool to help you assess

UM2501

STEVAL-BCN002V1 BlueTile sensor node

UM2501 - Rev 3

• The integrated SMD antenna needs clearance area and passives for proper tuning (FT1, FT2 and MT).

•

The Pi-network is only intended for flexibility and for testing. It is not populated as the integrated balun provides the necessary matching.

• The 32kHz crystal allows lower power consumption BLE Sleep Mode.

• The inductor allows lower power consumption in BLE Active Mode.

• The STEVAL-BCN002V1 BlueTile sensor node is supplied with the default firmware (BLE_SensorDemo, available in the SDK) already loaded. The firmware enables the streaming of sensor data to the reference smartphone app (ST BlueMS, available on Android™ and iOS™ stores).

page 3/44

RESETN

UART RX

UART TX

SWD CLK

SWD IO

IO IO IO IO

GND

BOOT

GND GND VDD

UM2501

System architecture

Figure 3. STEV

1a. BlueNRG-2 Bluetooth 5.0 network and application processor 1b. BALF-NRG-02D3 integrated balun and matching network 2a. LPS22HH ambient pressure sensor 2b. LSM6DSO smart accelerometer and gyroscope 2c. LIS2MDL magnetometer 2d.

VL53L1X proximity by time-of-flight 2e. HTS221 relative humidity and temperature 2f. MP34DT05-A top-port digital microphone

3a. User button 3b. RGB LED 4a. I2C SCL 4b. I2C SDA 4c. GND 4d. ADC 4e. TEST 4f. VDD 4g. GND 4h. RFTEST 5a. II-network (not mounted) 5b. SMD antenna 6a. Inductor to enable lowest power BLE active mode 6b. 32kHz crystal to enable lowest power BLE sleep mode 7a. Battery holder 7b. CR2032 battery (not included)

8. 10-pin connector

FCC ID: S9NSTEBCN2V1 IC ID: 8976C-STEBCN2V1

AL-BCN002V1 sensor node front and rear components

The BlueTile sensor node is supplied with the firmware already loaded. The default firmware includes two libraries:

MotionFX fusion library for orientation estimation (visualized with a rotating cube).

2. BlueVoice library to stream the voice captured by the MEMS microphone over the BLE connection (reproduced by the smartphone speaker, if not in vibration mode).

The STBLESensor app can be used to plot and log sensor data in real time on your smartphone.

2.1 System architecture

The BlueTile is powered by a coin-cell battery (CR2032). The voltage is not regulated because the sensors and the BlueNRG-2 embedded linear power regulator and switching mode power converter (DC-DC).

2.1.1 Power section for BlueNRG-2

The BlueNRG-2 in active mode can use the embedded linear voltage regulator (LDO) or the embedded DC-DC converter (DC-DC).

•

LDO regulator [Active mode, CPU Flash and RAM on]:

– RX 14.5 mA at 3 V, TX 17.2 mA when output power is +2 dBm

– range is 12-28.8 mA when output is -14 to +8 dBm

• DC-DC converter [Active mode, CPU Flash and RAM on]:

– RX 7.7 mA at 3 V, TX 9 mA at 3 V when output power is +2 dBm

– range is 6.6-15.1 mA when output is -14 to +8 dBm

UM2501 - Rev 3

can all operate at the voltage range of the battery. In any case, the BlueNRG-2 has its own

page 4/44

System architecture

Note: The BlueTile sensor node includes the inductor needed by the DC-DC converter to allow lower power

consumption in active mode.

In Sleep Mode, the BlueNRG-2 device can use its internal 32 kHz ring oscillator (RO) or the external 32 kHz crystal oscillator (XO) available on the BlueT mode:

• Sleep Mode [32 kHz ring oscillator, 24 kB RAM retention]: 2.1 µA at 3 V

• Sleep Mode [32 kHz crystal oscillator, 24 kB RAM retention]: 0.9 µA at 3 V

ile sensor node, which offers lower power consumption in sleep

2.1.2 Radio frequency section

The radio frequency section of the BlueTile includes the following elements:

A BALF-NRG-02D3 ultra-miniature balun which integrates matching network and harmonics filter.

2. A Pi-network which allows additional filtering and provides access points for testing.

Note: This network is not populated, as the integrated balun provides the necessary matching.

3. An SMD 2.4 GHz antenna, which requires a certain clearance area on the PCB and specific passives for precise tuning (FT1, FT2 and MT).

2.1.3 MEMS sensor section

The MEMS sensor section of the BlueTile sensor node includes inertial and environmental MEMS sensors connected with the BlueNRG-2 via an I2C bus operating at 400 kHz.

The MEMS microphone is connected with BlueNRG-2 through a dedicated line to transfer the PDM (Pulse Density Modulated) stream at 1.6 MHz, which is converted to PCM (Pulse Coded Modulation) by the integrated digital filter in the ADC block on the BlueNRG-2.

All sensors can generate interrupts, but only the interrupts from the LIS2MDL magnetometer and the LSM6DSO accelerometer and gyroscope are connected with the BlueNRG-2 through dedicated and independent lines.

•

The LIS2MDL magnetometer interrupt line is push-pull only and must have its own independent line. The interrupt pin of this sensor is connected with BlueNRG-2 to enable applications such as “reed-switch”, which is activated by an external magnet.

• The LSM6DSO smart accelerometer and gyroscope interrupt pin is an input at boot. It has an internal pulldown. If the pin is low at boot, the I2C interface is selected, otherwise the I3C interface is selected. The pin can be reconfigured as open-drain, but the external pull-up would cause additional power consumption. The interrupt pin of this sensor is connected to BlueNRG-2 to exploit the smart embedded processing functionality (single/double tap recognition, free-fall, wakeup, portrait/landscape, 6D/4D orientation detection; activity/inactivity, stationary/motion detection; pedometer, step detector and step counter; up to 16 finite state machines to process).

• The LPS22HH barometer interrupt pin exhibits the same behavior as the LSM6DSO interrupt pin: it is an input pin at boot and must be low to activate the I2C interface. It can be configured as push-pull or opendrain after boot. The interrupt pin of this sensor is not connected to BlueNRG-2.

• The HTS221 relative humidity and temperature interrupt pin is push-pull at boot and can be reconfigured as open-drain after boot. The interrupt pin of this sensor is not connected to BlueNRG-2.

• The VL53L1X time-of-flight proximity interrupt line is open-drain only and would require an external pull-up. The interrupt pin of this sensor is not connected to BlueNRG-2.

The dynamics of the environmental parameters are relatively slow, so interrupts are not necessary. The application only needs to wake up every few seconds and perform one-shot measurements with the LPS22HH barometer or HTS221 relative humidity and temperature sensor, and trigger an action if specific conditions are met.

It is also not convenient to keep the VL53L1X proximity time-of-flight sensor active, the power consumption or the latency would be too high. The power consumption of VL53L1X ranges from 0.5 mA for 1 Hz measurements, up to 7 mA for 10 Hz measurements.

UM2501

2.1.4 Pinout descriptions

In the following figure, you can see 6 pads along the edge of the board:

•

RFTEST (4h) and GND (4g) connected to the RF section for test purposes.

• TEST (4e) connected to the analog TEST output of BlueNRG-2 for test purposes.

• VDD (4f) and GND (4c), for test purposes or to power additional external components.

• ADC (4d) to accept analog input signals from additional external components.

UM2501 - Rev 3

page 5/44

RESETN

UART RX

UART TX

SWD CLK

SWD IO

IO IO IO IO

GND

BOOT

GND GND VDD

Features of the BlueNRG-2 device

• I2C SCL (4a) and I2C SDA (4b) to connect additional external components via I2C.

UM2501

Figure 4. STEV

VL53L1X proximity by time-of-flight 2e. HTS221 relative humidity and temperature 2f. MP34DT05-A top-port digital microphone

8. 10-pin connector

FCC ID: S9NSTEBCN2V1 IC ID: 8976C-STEBCN2V1

AL-BCN002V1 sensor node front and rear components

On the debug connector on the rear of the board, there are 10 pins:

VDD (pin 2) and GND (pin 4, 6, 10) to accept power from the host motherboard.

•

• SWD IO (pin 1) and SWD CLK (pin 3) to Flash and debug through the host motherboard.

– SWD pins can be used as digital GPIOs when the BlueTile is not connected to its host board.

• UART TX (pin 5) and UART RX (pin 7).

– UART pins can be used as digital GPIOs when the BlueTile is not connected to its host board.

• BOOT (pin 8) and RESETN (pin 9) to control the boot and keep BlueNRG-2 under reset.

– The boot pin can also be used as a digital GPIO when the BlueTile is not connected to its host board,

but it needs to be pull-down at start-up.

2.2 Features of the BlueNRG-2 device

BlueNRG-2 integrates a Bluetooth Low Energy radio (BLE), an ARM® Cortex®-M0 core, 12+12 kB of RAM,

UM2501 - Rev 3

256 kB of Flash memory fast 400 kHz), UART interfaces; two multi-function timers (MFT), a DMA controller, RTC and watchdog, and an ADC with PDM stream processor.

The public key cryptography (PKA) and random number generator (RNG) are reserved for the BLE protocol stack, but the user application can also read the RNG.

The ADC is 10-bit and features single or continuous acquisition at max. 1 MHz sampling frequency, two single ended or one differential signal (ADC1 and ADC2 pins), embedded channels for temperature and battery voltage sensing, embedded digital filter with down sampling. The embedded digital filter can be used to process the PDM stream from a digital MEMS microphone (1.6 MHz or 0.8 MHz) and convert it to audio PCM (8 kHz to 50 kHz when 1.6 MHz clock is used for the microphone).

BlueNRG-2 uses the embedded digital filter of the ADC peripheral for PDM to PCM conversion when reading the

PDM output of the MEMS microphone MP34DT05-A.

, SPI (max 1 MHz in slave mode, 8 MHz in master mode), two I2Cs (standard 100 kHz or

page 6/44

The low-speed clock is used in low-power mode and can be supplied by the internal RC oscillator or by an external crystal (32 kHz ±50 ppm). The high-speed clock is supplied by a fast-starting internal RC oscillator (16 MHz) while the external crystal is starting up. The high-speed external crystal (16 or 32 MHz) is required to enable the BLE radio.

Only the 32 MHz XO can support the highest computational loads, allowing the Cortex-M0, the DMA and the APB tree to run at 32 MHz, while the rest of the clock tree runs at 16 MHz. When a 16 MHz XO is used, the Cortex-M0 and all the clock tree runs at 16 MHz.

2.2.1 BlueNRG-2 states

• Preactive:

–

After power-on-reset, all digital power supplies are stable.

– Internal 16 MHz and 32 kHz RC oscillators are used.

– Reachable from Reset, Standby and Sleep states.

– Goes to Active state.

• Active:

– The external high-frequency crystal is used (16 MHz ±50ppm or 32 MHz) to enable BLE

communication.

– Internal 16MHz RC oscillator is switched off

– BlueNRG-2 uses a 32 MHz ±10ppm crystal (higher crystal accuracy = lower power consumption).

– The radio can be activated for transmission (TX) or reception (RX). This is the state used by

BlueNRG-2 when the user application is running or there is a BLE event to serve.

– The programmed GPIO configuration is restored.

– reachable only from Preactive only.

• Standby:

– RAM retention is used (12 or 24 kB).

– 5 different GPIOs can be used to wake-up: IO9, IO10, IO11 with an internal pull-up; IO12, IO13 which

require an external drive).

– BlueNRG-2 IO11 is connected to the user button, IO12 connected to the interrupt pin of LIS2MDL

magnetometer, and IO13 connected to the interrupt pin of the LSM6DSO accelerometer and gyroscope.

– Wake-up time is typically 200µs.

– reachable from Active.

– can go to Preactive.

• Sleep:

– RAM retention is used (12 or 24 kB).

– The low-frequency oscillator is switched on to serve periodic BLE connection events.

– 5 different GPIOs can also be used to wake-up, as in Standby state.

– This is the state used by the BlueNRG-2 tile to save power when the user application is not running

and the device is waiting for a BLE event to serve.

– The programmed GPIO configuration is not maintained (this may affect connected sensors; for

example, see pin IO7 of BlueNRG-2 connected to XSHUT pin of VL53L1X).

– Reachable from Active.

– Can go to Preactive.

UM2501

Features of the BlueNRG-2 device

2.2.2 BLE firmware stack and memory map

Program memory, data memory, registers and I/O ports are organized in a linear 32-bit address space.

•

The SRAM is divided in two banks:

– 12 KB from 0x2000_0000 to 0x2000_2FFF (retention always-on).

– 12 KB from 0x2000_3000 to 0x2000_5FFF (retention optional).

– The FULL BLE stack needs 9.6 KB of SRAM.

– The BASIC BLE stack needs 8.0 KB of SRAM.

UM2501 - Rev 3

page 7/44

UM2501

Inertial MEMS sensors

• The Flash is 256 KB from 0x1004_0000 to 0x1007_FFFF

–

The FULL BLE stack needs 77 KB, leaving 179 KB for the user application. The FULL BLE stack supports concurrent peripheral and central roles (N=0,1,2 connections to other centrals and 8-N connections to other peripherals), LE secure connections, controller privacy, and extended data length.

– The BASIC BLE stack needs 58 KB, leaving 198 KB for the user application. The BASIC BLE supports

the peripheral role only (1 connection to a central), legacy security only, no controller privacy and no extended data length.

– The OTA manager for over-the-air firmware updates adds 10 KB to the size of the BLE stack.

The OTA manager may be independent of the user application, or embedded in the user application:

• When the OTA manager is independent of the user application, the Flash is divided in two sections:

1. A relatively small section for the OTA application; the size is the sum of the BLE stack size and the

OTA manager size.

2. A larger section for the user application.

• When the OTA manager is embedded in the user application, the Flash is divided in three sections:

1. A section that holds the current application; the size is the sum of BLE stack size, OTA manager size

and user application size.

2. A section for the new updated application; the size is the same as the first section.

3. A very small section for the reset application that decides decides which application to run after boot,

depending on what is available and valid in the first two sections.

An independent OTA manager leaves more room for the user application, but there is no application to run if the update does not finish successfully.

An embedded OTA manager can still use the previous application if the update does terminate successfully, but the space available for the user application is less than half the size of the Flash.

Note: After a successful update, the new application can be copied over the old application, or the role of the first two

sections can be exchanged.

2.3 Inertial MEMS sensors

Each sensor is made of a Micro Electro Mechanical system (MEMS) with a sensing element and a dedicated ASIC with analog acquisition chain, analog-to-digital converter (ADC), and digital signal processing (DSP) and control logic.

2.3.1 LSM6DSO 3D accelerometer and 3D gyroscope

2.3.1.1 LSM6DSO interrupts

The LSM6DSO delivers best-in-class motion sensing able to support more sophisticated functionality than simply orienting devices to portrait and landscape mode.

The following event-detection interrupts are supported:

•

Free-fall event:

– detected when acceleration data from all enabled axes are below threshold settings for a certain

duration

• Wake-up event:

– detected when the filtered data from any of the enabled axes are above threshold settings for a certain

duration

– choose between high-pass filtered data, slope detection filter (difference between consecutive

samples, divided by two), low-pass filtered data plus an offset for each axis, or unfiltered data plus an offset.

• 6D/4D orientation event:

– detected when an axis (positive or negative) is above the threshold setting, while the other two are

below the threshold for a certain duration

– 4D is a subset of 6D; the Z axis is not used.

– choose between unfiltered data or low-pass filtered data

UM2501 - Rev 3

page 8/44

UM2501

Inertial MEMS sensors

• Single/double tap event:

–

detected when the output of the slope detection filter exceeds the threshold setting and then returns below the same setting within a “shock” time interval

– double tap event is detected when a first tap is detected and a second tap is detected after a “quiet”

time interval, but before a maximum “duration” interval

– for reliable detection, configure the device to use a high sampling rate, like 400 Hz.

– if two or more enabled axes are over their respective thresholds, the axis with the highest priority

setting is used

– can be used to enable user interaction in addition to the button present on the BlueTile

• Activity/inactivity event:

– uses the same data as the wake-up event

– if inactivity is detected (data below the threshold setting for a certain time interval), the device

automatically goes to Low-power Mode and reduces the accelerometer sampling rate down to 12.5 Hz to minimize power consumption

– if a wake-up event is detected, the device automatically returns to the programmed accelerometer

operating mode and sampling rate

– can be configured to put the gyroscope in power-down or sleep mode when the accelerometer is in

low-power mode

• Stationary/motion event

• a special activity/inactivity event in which event detection is the same, but the device does not change power mode or sampling rate

2.3.1.2 LSM6DSO advanced functionality

Certain digital processing blocks allow advanced functions and algorithms when the output data rate is 26 Hz or higher

• Pedometer functions: step detector and step counter.

– when a step is detected, an interrupt is generated and a corresponding counter is incremented by 1

(max value is 65535)

– can also set the interrupt to only be triggered when at least one step is detected in a configurable time

interval

– de-bounce functionality to avoid false detections, where N consecutive steps are detected before the

first interrupt is generated (default is N=10)

– two additional blocks can facilitate the identification of false-positives:

only trigger when statistical data matches the walking pattern

adapt the embedded algorithm to slow pace walking patterns

• Significant motion detection: to signal a possible change in user location

– based on the pedometer function, which is automatically enabled

– interrupt is generated when the difference between the number of steps after initialization or reset is

higher than the de-bounce threshold (default is 10).

– function is reset after each interrupt

• Relative tilt detection

– generates an interrupt when there a change in the tilt of the device exceeds 35 degrees

– reference position is set when the detection logic is enabled and reset when the interrupt is generated

– detection logic requires a 2-second settling time after it is enabled or re-initialized

2.3.1.3 LSM6DSO finite state machines

The LSM6DSO can run up to 16 simultaneous finite state machines (FSMs) that consist of a sequence of instructions or actions (parameter setting, interrupt generation, etc.), or a RESET

• if the RESET condition is satisfied, the FSM returns to the reset point

• if the NEXT condition is satisfied, the FSM moves to the next instruction

• otherwise, the RESET-NEXT conditions are re-tested.

FSM data may be accelerometer, gyroscope, integrated gyroscope or external sensor data, and can be decimated. A data vector consists of X, Y, Z values and a vector norm V (square root of sum of squares).

UM2501 - Rev 3

-NEXT condition:

page 9/44

Each FSM has the following features:

•

3 different 8-bit masks to allow tests on positive and negative values of X, Y, Z and V.

• 3 different thresholds and 1 programmable hysteresis value that is automatically added to or subtracted from the selected threshold based on the test condition.

• 4 different counters/timers to manage event durations.

2.3.1.4 LSM6DSO smart FIFO buffer

The LSM6DSO accelerometer has a first-in first-out (FIFO) data buf words of 7 bytes each (1 tag byte plus 6 data bytes). The tag drives the decoding and includes a parity bit for validation, while the data can derive from any combination of accelerometer, gyroscope, up to 4 external sensors, embedded temperature sensor, timestamp counter and pedometer step counter. The data rates can be set independently for each source.

For the accelerometer, you can choose to store high-pass filtered data, slope detection filter data, low-pass filtered data or unfiltered data plus an optional offset (independent for each axis). The low and high-pass filters are configurable.

For the gyroscope, you can enable a first optional high-pass filter, and a second optional and programmable lowpass filter.

To maximize the amount of data stored in the FIFO, you can enable an adaptive lossless delta pulse-codedmodulation (DPCM) compression algorithm for the accelerometer and the gyroscope data. When the difference between consecutive data words is small, instead of sending a new data word (16 bits/axis), only the difference with respect to the previous is sent (8 bits = 2:1 compression or 5 bits/axis = 3:1 compression).

When DPCM compression is enabled, it is also possible to select when DPCM is reset by storing uncompressed data in the FIFO: never, every 8, 16 or 32 words. This is useful when the FIFO is used as a circular buffer (Continuous mode) and words may be overwritten, as the decoder can only work if previous data words can be traced back to an uncompressed data word for reference.

DPCM compression works on 3 data words (sampled at time t, t-1 and t-2) and introduces a latency of 2 data words. The compression factor depends on the difference between a data word and the previous data word.

• When DPCM is disabled, the compression buffer is flushed and the output is the non-compressed data word at time t-2, then data word at time t-1 and data words at current time t thereafter (tag “NC_T_2”, “NC_T_1”, and “NC”).

• When DPCM is enabled, the first output is the non-compressed data word at time t-2 (tag “NC_T_2”), used as the reference to start decoding. Subsequent outputs depend on D2 (difference between data word at t-2 and previous decoded word), D1 (difference between data word at t-1 and t-2), and D0 (difference between data word at t and t-1):

– If any difference in D2 exceeds 128 LSB on any axis:

◦ the uncompressed data word at time t-2 is written to the FIFO by storing the 16-bit signed value of

each axis (low and high bytes for X, Y and Z: XL XH YL YH ZL ZH, for a total of 6 bytes)

◦ tag NC_T_2

– If any difference in D2 and D1 exceeds 16 LSB, but is within 128 LSB for all axes:

◦ a 2:1 compression ratio is applied by storing the 8-bit signed difference to reconstruct 2 data

values for each axis at time t-1 and t-2 (D1x D1y D1z, then D2x D2y D2z, for a total of 6 bytes)

◦ tag 2xC

◦ the data at time t-2 is derived by summing D2 to the previously decoded data word

◦ the data at time t-1 is derived by summing D1 to the data at time t-2 just derived

– If all differences in D2, D1 and D0 are within 16LSB for all axis:

◦ a 3:1 compression ratio is applied by storing the 5-bit signed difference to derive 3 data values for

each axis at time t, t-1 and t-2 (D0x D0y D0z and a dummy bit to make 16 bits, then D1x D1y D1z and a dummy bit, then D2x D2y D2z and a dummy bit, for a total of 6 bytes)

◦ tag 3xC

◦ the data at time t-2 is derived by summing D2 to the previous decoded data word

◦ the data at time t-1 is derived by summing D1 to the data at time t-2 just derived

◦ the data at time t is derived by summing D0 to the data at time t-1 just derived

Interrupts can be generated when the FIFO buffer stores a given number of samples (FIFO threshold level), or when it is full, or when it overflows (overrun). The FIFO can work in the following modes:

UM2501

Inertial MEMS sensors

fer that can store up to 3 KB of data, or 512

UM2501 - Rev 3

page 10/44

Inertial MEMS sensors

• Bypass Mode:

–

the FIFO buffer is disabled and cleared

• FIFO Mode:

– the FIFO buffer collects data until it is full, then stops

• Continuous Mode:

– the FIFO buffer collects data continuously

– when it is full, the oldest samples are overwritten as in a circular buffer

– FIFO full and FIFO threshold level interrupts allow the host microcontroller to read the data before it is

overwritten

• Continuous-to-FIFO Mode:

– the FIFO buffer collects data continuously but switches to FIFO Mode as soon as the selected interrupt

occurs

– this mode is especially useful to capture data before and after a specific event

• Bypass-to-Continuous Mode:

– the FIFO buffer is disabled, but switches to Continuous Mode as soon as the selected interrupt occurs

– this mode is useful to capture data after an event has occurred

• Bypass-to-FIFO Mode:

– the FIFO buffer is disabled, but switches to FIFO mode as soon as the selected interrupt occurs

– this mode is useful to capture data after an event has occurred

– data collection stops once the FIFO is filled

UM2501

UM2501 - Rev 3

page 11/44

2.3.2 LIS2MDL 3-axis magnetometer

2.3.2.1 LIS2MDL dynamic range, resolution and accuracy

The LIS2MDL Gauss if the magnetic field is not aligned with one of the axes), which is well above Earth’s magnetic field (which is typically in the range of 0.25 to 0.65 Gauss).

The output is 16 bits (1.5 mGauss/LSB ±7%), and the RMS noise level in High-performance Mode is 3 mGauss (2 LSB). The high resolution and accuracy allows e-compass orientation estimation and distance measurements from a reference magnet (in its simplest form, the magnetometer can emulate a magnetically activated Reedswitch).

The LIS2MDL magnetometer can perform a single-shot measurement and then return to Power-down Mode, or operate in Continuous Mode with a programmable sampling rate (10, 20, 50 or 100 Hz).

Single-shot measurements can be performed at max. 100 Hz in high-performance mode, or max. 150 Hz in lowpower mode. In low-power mode, the power consumption is reduced to 25%, while in high-performance mode the RMS noise is halved. An optional low-pass filter can be activated to further reduce RMS noise, without increasing the power consumption, the bandwidth in this case is reduced from output data rate ODR/2 down to ODR/4.

2.3.2.2 LIS2MDL intrinsic offset automatic cancellation

The LIS2MDL an initial operating condition; a reset pulse may be used to enable the compensation of the intrinsic magnetic offset.

• If intrinsic offset compensation is disabled, there is no reset pulse. The set pulse can be generated at poweron only (Set_FREQ=1), or every 64 measurements (Set_FREQ=0).

• If intrinsic offset compensation is enabled, set and reset pulses are generated alternately on consecutive samples. After the set pulse, the measured output is the magnetic field H plus offset; after the reset pulse, the measured output is H minus offset.

– In Continuous Mode, the device averages consecutive measurements to compensate for the offset, the

– output =

– In Single-shot Mode, the host microcontroller averages two consecutive measurements. The averaged

When intrinsic offset compensation is performed, the residual offset is in the range of ±60 mgauss, and the dependency on temperature is ±0.3 mgauss/°C.

is a 3D digital magnetometer with a ±50 Gauss dynamic magnetic field range (reduced to ±25

is based on anisotropic magneto-resistive (AMR) technology, in which a set pulse is required to set

output will be equal to the magnetic field H.

ffset

H + o

+ H − offset

= H

measurements must occur within a short time of each other for the compensation to be ef

UM2501

Inertial MEMS sensors

fective.

2.3.2.3 LIS2MDL extrinsic offset (hard iron) compensation

Hard-iron compensation is a constant offset added to magnetic field measurements to compensate distortion caused by ferromagnetic materials or high currents. This of analysing the output of the magnetometer.

When it is available, this offset can be programmed in specific registers (OFFSET_X_REG_H/L, OFFSET_Y_REG_H/L, OFFSET_Z_REG_H/L) so that it is automatically subtracted by the LIS2MDL device.

2.3.2.4 LIS2MDL interrupt generation

The LIS2MDL the subtraction of hard-iron offset) exceeds a programmed threshold (INT_THS_H/L_REG) in the positive or negative direction.

Comparisons can be enabled independently for each axis (XIEN, YIEN, ZIEN flags):

• when the output data is above the positive threshold, the corresponding flag is set (P_TH_S_X/Y/Z)

• when the output data is below the negative threshold, the corresponding flag is set (N_TH_S_X/Y/Z).

A specific interrupt can be generated if there is a measurement range overflow at the internal ADC.

magnetometer sensor can be configured to generate an interrupt when output data (before or after

fset can be computed by the host microcontroller by

UM2501 - Rev 3

page 12/44

2.4 Environmental MEMS sensors

2.4.1 LPS22HH barometer

2.4.1.1 LPS22HH acquisition chain

The LPS22HH pressure sensor can perform a one-shot measurement and then return to Power-down Mode, or it can operate in Continuous Mode with a programmable sampling rate (1, 10, 25, 50, 75, 100 or 200 Hz).

Measurements can be taken in normal Low-noise Mode, or in Low-power Mode to minimize current consumption. When continuous mode is selected, Low-noise Mode is not available at 100 and 200 Hz. In all cases, an optional low-pass filter can be enabled with a programmable cutoff frequency to reduce the noise level (the bandwidth is reduced from output data rate ODR/2 down to ODR/9 or ODR/20).

The low-pass filter is reset when it is enabled. After reset, a specific settling time is required before the first accurate sample on the output is available (9 or 20 samples must be discarded, respectively).

Two programmable offsets can be subtracted from measured data:

• First, offset compensation (always): the offset measured with one-point calibration (OPC) can be stored in specific registers (RPDS) and then subtracted from subsequent measurements (OPC-compensated data = data – RPDS*256). The low-pass filter, if enabled, will filter OPC-compensated data. Filtered and unfiltered OPC-compensated data is stored in the FIFO.

• Second, auto-zero mode (optional): the offset-compensated (and possibly filtered) pressure measurements are stored in specific registers (REF_P) when auto-zero is enabled (AUTOZERO or AUTOREFP set to 1) and then subtracted from subsequent measurements (AZ-compensated data = data – REF_P). Filtered and unfiltered OPC-compensated data or AZ-compensated data is stored in output registers.

UM2501

Environmental MEMS sensors

2.4.1.2 LPS22HH interrupt generation and FIFO buffer

The LPS22HH pressure sensor can be configured to generate interrupt events related to pressure acquisitions and FIFO status (watermark reached, full, overrun, etc.).

The interrupt can be generated when a new pressure or temperature sample is available, or when the AZcompensated data exceeds a programmed threshold (THS_P) in the positive (PHE flag enables the comparison with +THS_P) or negative (PLE flag enables the comparison with –THS_P) direction. The following configurations are available:

AUTOZERO=0 and AUTOREFP=0: interrupt logic is disabled; filtered and unfiltered OPC-compensated data goes to FIFO and output registers.

2. AUTOZERO=1: interrupt logic is enabled; REF_P is set when interrupt is enabled; AZ-compensated data goes to the interrupt logic and to the output registers, while filtered and unfiltered OPC-compensated data goes to FIFO.

3. AUTOREFP=1: interrupt logic is enabled; REF_P is set when interrupt is enabled; AZ-compensated data goes to interrupt logic, while filtered and unfiltered OPC-compensated data goes to FIFO and output registers.

The FIFO buffer can store up to 128 pressure samples (24 bits each) and 128 temperature samples (16 bits each). FIFO depth can be limited by stopping at the programmable watermark level. The FIFO can work in the following modes:

• Bypass Mode:

– the FIFO buffer is disabled and cleared

• FIFO Mode:

– the FIFO buffer collects data until it is full or the watermark setting is reached, then stops

• Continuous (or Dynamic Stream) Mode:

– the FIFO buffer collects data continuously

– when it is full or the watermark setting is reached, the oldest samples are overwritten as in a circular

buffer

– FIFO full and FIFO threshold level interrupts allow the host microcontroller to read the data before it is

overwritten

UM2501 - Rev 3

page 13/44

Environmental MEMS sensors

• Continuous (Dynamic Stream)-to-FIFO Mode:

–

the FIFO buffer collects data continuously but switches to FIFO Mode as soon as the selected interrupt occurs

– this mode is especially useful to capture data before and after a specific event

• Bypass-to-Continuous (Dynamic Stream) Mode:

– the FIFO buffer is disabled, but switches to Stream Mode as soon as the selected interrupt occurs

– this mode is useful to capture data after an event has occurred

• Bypass-to-FIFO Mode:

– the FIFO buffer is disabled, but switches to FIFO mode as soon as the selected interrupt occurs

– this mode is useful to capture data after an event has occurred

UM2501

UM2501 - Rev 3

page 14/44

+ 30 hidden pages