PNI SENtral User Manual

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SENtral

Motion Coprocessor

General Description

The SENtral Motion Coprocessor is a custom integrated circuit that makes it easy to quickly incorporate, optimize and operate multiple motion sensors on mobile consumer electronics devices. SENtral employs and manages a user-specified 3-axis magnetometer, 3–axis accelerometer, and 3–axis gyroscope to provide reliable motion tracking, and accurate heading and orientation data. SENtral gathers data from the individual sensors, then integrates and fuses this data using PNI’s proprietary Kalman filtering and heuristic algorithms.

Features

 Heading Accuracy of 2° rms.  Ultra Low Power Consumption  Continuous Soft and Hard-Iron

Magnetic Auto-Calibration

 Magnetic Anomaly

Compensation

 I2C Interface – 100 to 3400 kHz  Small Form-Factor  Sensor Flexibility

By offloading the sensor fusion and interface from a dedicated sensor hub MCU or the host CPU to SENtral, overall power requirements are dramatically lowered and processing power is opened up for other uses.

These advantages make SENtral the ideal choice for mobile and consumer electronics devices desiring ultra-lower power consumption and best-in-class sensor fusion.

Applications

 Cell Phones  Tablets  Ultrabooks  TV Remote Controls  Video Game Controllers

Ordering Information

Table of Contents

1 PRODUCT OVERVIEW ............................................................................................... 3

1.1 SENTRAL FEATURES AND BENEFITS ........................................................ 3

1.2 SENTRAL FUNCTIONAL DESCRIPTION ...................................................... 4

2 SENTRAL SPECIFICATIONS ..................................................................................... 6

2.1 PERFORMANCE CHARACTERISTICS ......................................................... 6

2.2 ELECTRICAL CHARACTERISTICS ............................................................... 6

3 LAYOUT ....................................................................................................................... 8

3.1 SYSTEM LAYOUT .......................................................................................... 8

3.2 PIN ASSIGNMENTS ....................................................................................... 9

3.3 SENSOR LAYOUT ........................................................................................ 10

3.4 DEDICATED EEPROM (OPTIONAL) ........................................................... 11

4 I2C INTERFACE ......................................................................................................... 12

4.1 I2C TIMING .................................................................................................... 12

4.2 I2C HOST INTERFACE (HOST BUS) ........................................................... 13

4.2.1 I2C Slave Transfer formats ............................................................... 14

4.3 I2C SENSOR INTERFACE (SENSOR BUS) ................................................. 15

4.4 I2C PULL-UP RESISTANCE ......................................................................... 15

5 OPERATION .............................................................................................................. 16

5.1 POWER-UP AND CONFIGURATION FILE UPLOAD .................................. 17

5.1.1 Configuration File Upload from EEPROM ........................................ 17

5.1.2 Configuration File Upload from Host ................................................ 19

5.2 INITIAL REGISTER SET-UP ......................................................................... 20

5.3 RUNNING IN NORMAL OPERATION .......................................................... 22

5.3.1 Error .................................................................................................. 23

5.3.2 CPUReset ......................................................................................... 24

5.3.3 Read Results .................................................................................... 24

5.4 STANDBY STATE ......................................................................................... 25

5.5 PASS-THROUGH STATE ............................................................................. 25

5.6 TROUBLESHOOTING .................................................................................. 27

5.6.1 Hardware-Related Error Conditions ................................................. 27

5.6.2 Software-Related Error Conditions ................................................... 27

6 SENTRAL CONFIGURATION TOOL ........................................................................ 30

6.1 CONFIGURATION TOOL GENERAL SETTINGS ........................................ 31

6.1.1 SDK Revision ................................................................................... 31

6.1.2 Host Interrupt Pin .............................................................................. 31

6.1.3 EEPROM Max. Upload Speed ......................................................... 31

6.2 CONFIGURATION TOOL SENSOR CONFIGURATION .............................. 31

6.2.1 Sensor .............................................................................................. 31

6.2.2 Interrupt Pin ...................................................................................... 31

6.2.3 Slave Address .................................................................................. 31

6.2.4 Orientation Matrix ............................................................................. 32

6.2.5 Cal Offsets ........................................................................................ 33

7 PACKAGE INFORMATION ....................................................................................... 34

8 ASSEMBLY GUIDELINES ......................................................................................... 36

APPENDIX I – CONFIGURATION FILE IMAGE FORMAT.................................................... 39

APPENDIX II – CONVERTING QUATERNIONS ................................................................... 41

APPENDIX III – PARAMETER TRANSFER ........................................................................... 43

APPENDIX IV – SAMPLE SCHEMATIC SET ........................................................................ 49

PNI Sensor Corporation Doc #1018049 R03 SENtral Technical Data Sheet Page 1

List of Figures

Figure 1-1: SENtral Block Diagram .......................................................................................... 4

Figure 3-1: SENtral System Reference Schematic .................................................................. 8

Figure 4-1: I2C Timing Diagram .............................................................................................. 12

Figure 4-2: I2C Slave Write Example ...................................................................................... 14

Figure 4-3: I2C Slave Read Example, with Repeated START................................................ 14

Figure 4-4: I2C Slave Write Register Address Only ................................................................ 14

Figure 4-5: I2C Slave read register from current address ....................................................... 14

Figure 5-1: SENtral Initialization Sequence ............................................................................ 16

Figure 5-2: SENtral Operational States .................................................................................. 17

Figure 5-3: SENtral Normal Operation Flow ........................................................................... 22

Figure 6-1: SENtral Configuration Tool .................................................................................. 30

Figure 7-1: Mechanical Drawing ............................................................................................. 34

Figure 7-2: Tape Dimensions ................................................................................................. 35

Figure 8-1: Typical Solder Mask and Land Pad Parameters ................................................. 37

Figure 8-2: Typical Solder Reflow Profile ............................................................................... 38

Figure A3-1: Parameter Load Process ................................................................................... 44

Figure A3-2: Parameter Retrieve Process ............................................................................. 45

List of Tables

Table 2-1: Performance Characteristics ................................................................................... 6

Table 2-2: Absolute Maximum Ratings .................................................................................... 6

Table 2-3: Operating Conditions............................................................................................... 7

Table 3-1: SENtral Pin Assignments ........................................................................................ 9

Table 3-2: Recommended Power Line Distance from Magnetometer ................................... 11

Table 4-1: I2C Timing Parameters .......................................................................................... 13

Table 4-2: I2C Pull-Up Resistance Table ................................................................................ 15

Table 5-1: Configuration File Upload from EEPROM Registers ............................................ 18

Table 5-2: Configuration File Host Upload Registers ............................................................. 19

Table 5-3: Sample Host Upload Data Order .......................................................................... 20

Table 5-4: Registers for Initial Set-Up .................................................................................... 20

Table 5-5: Normal Operation Registers .................................................................................. 23

Table 5-6: Results Registers .................................................................................................. 24

Table 5-7: Standby Registers ................................................................................................. 25

Table 5-8: Pass-Through Registers........................................................................................ 26

Table 5-9: Hardware-Related Error Indications ...................................................................... 27

Table 5-10: Software-Related Error Indications ..................................................................... 27

Table 5-11: SensorStatus Register Values ............................................................................ 28

Table 5-12: ErrorRegister Values ........................................................................................... 28

Table 5-13: RAMVersion Register Values .............................................................................. 29

Table 8-1: Typical Solder Processing Parameters ................................................................. 38

Table A1-1: Configuration File Image Format ........................................................................ 39

Table A1-2: Configuration File Data Structure ....................................................................... 40

Table A3-1: Registers Used for Parameter Transfer .............................................................. 43

Table A3-2: Parameter Numbers............................................................................................ 46

Table A3-3: DriverID & AlgorithmID Definition ....................................................................... 48

PNI Sensor Corporation Doc #1018049 R03 SENtral Technical Data Sheet Page 2

1 Product Overview

The SENtral Motion Coprocessor is an integrated circuit that makes it easy to quickly integrate, optimize and operate multiple sensors on mobile consumer electronics devices. SENtral manages and uses data from a user-specified 3-axis gyroscope, 3-axis accelerometer, and 3-axis magnetometer to provide reliable motion tracking and an accurate compass heading, while consuming about 1% of the power of a comparable sensor fusion microprocessor.

Note: This revision of the SENtral Technical Datasheet applies to Configuration Files of revision 1.1 or higher. The Configuration File is discussed in Sections 1.2, 5.1, 5.6.2, and 6, and Appendix I. It is generated by the SENtral Configuration Tool and is uploaded into SENtral RAM after power up.

1.1 SENtral Features and Benefits

Features and benefits of the SENtral Motion Coprocessor include:

 Low power consumption. Offloads sensor processing from the less efficient host

CPU, consuming <1% of the power of a Cortex M0 running a comparable sensor fusion algorithm. Provides the ability to tailor the tradeoff between power consumption and motion-tracking performance.

 Industry-leading heading accuracy. Unparalleled heading accuracy for consumer

electronics applications.

 Continuous hard and soft-iron magnetic auto-calibration. Provides continual

background calibration of the sensors. Leverages PNI’s more than 20 years of experience and expertise in magnetic measurement.

 Magnetic anomaly compensation. Heading and motion tracking is unaffected by

magnetic anomalies such as rebar in buildings, desks, speakers etc., that can easily throw off the accuracy. SENtral recognizes and compensates for these anomalies.

 Sensor flexibility. Works with common consumer electronic MEMS motion sensors,

so system designers can choose the sensors most appropriate for their systems.

 Small form-factor. 1.6x1.6x0.5 mm chip-scale package on 0.4 mm pitch. Uses little

PCB real estate, allowing for painless integration.

 I2C interface. Uses the industry-standard I2C protocol to interface to the sensors and

the host, so system integration is straightforward. Standard, Fast, Fast Plus, and High Speed are supported on the host bus.

 Outputs. SENtral outputs quaternions, Euler angles (heading, pitch, & roll), and

sensor data (rotational velocity, linear acceleration, & magnetic field).

PNI Sensor Corporation Doc #1018049 R03 SENtral Technical Data Sheet Page 3

1.2 SENtral Functional Description

Figure 1-1 provides a diagram of SENtral’s primary functional blocks, and a brief description of these functional blocks follows.

Figure 1-1: SENtral Block Diagram

 Quaternion generates the orientation output, where the actual orientation outputs can

be quaternions or Euler angles (heading, pitch, & roll). The outputs are updated at a rate limited to the gyro output data rate (ODR), to a maximum of 400 Hz.

 Kalman Update fuses data from the 3-axis gyroscope, 3-axis accelerometer, and 3-

axis magnetometer, plus data from the magnetic anomaly determination and continuous auto-calibration blocks to generate intelligent orientation updates. The Kalman update involves a sophisticated multi-state Kalman algorithm.

 Continuous Hard and Soft-Iron Auto-Calibration. SENtral is the only product in

the market that auto-calibrates for both hard-iron and soft-iron magnetic distortions. While others may calibrate for hard-iron distortion, soft-iron distortion is more difficult to correct for, and it can be caused by EMI shielding tape and other shielding materials widely used in mobile and consumer electronic devices. It is important to correct for soft-iron distortions since these can contribute up to 90° of error.

Additionally, since a host system’s magnetic signature can change over time and

temperature, SENtral’s continuous auto-calibration ensures accuracy all the time.

PNI Sensor Corporation Doc #1018049 R03 SENtral Technical Data Sheet Page 4

 Magnetic Anomaly Determination establishes if a transient magnetic distortion is

present and accounts for it.

 Configuration RAM allows for customizing SENtral to match the specific sensors

being used and allows the user to tailor certain parameters for their specific system. The SENtral Configuration Tool generates the SENtral Configuration File, and this is subsequently uploaded into SENtral’s Configuration RAM.

 Pass-Through allows for direct communication with devices on the sensor bus by

connecting SENtral’s I2C Host Interface to the Sensor Interface.

 Host Interface communicates with the host system. Data is transmitted between the

host and SENtral via the host I2C bus, in which the host acts as the master and SENtral acts as a slave device. SENtral signals the host that new data is available by sending an interrupt signal on the host DRDY line.

 Sensor Interface communicates primarily with the sensors. Sensor data is

transmitted from the sensors to SENtral via the sensor I2C bus, in which SENtral acts as the master and the sensors as the slave devices.

PNI Sensor Corporation Doc #1018049 R03 SENtral Technical Data Sheet Page 5

Parameter

Minimum

Typical

Maximum

Units

Heading Accuracy

° rms

Output Data Rate

200

400

Parameter

Symbol

Minimum

Maximum

Units

Supply Voltage

VDD

-0.3

+3.6

VDC

Input Pin Voltage

VIN

GND – 0.3

VDD + 0.3

VDC

ESD Human Body Model

HBM

-2000

+2000

Machine Model

-200

+200

Storage Temperature

-50°

+150°

2 SENtral Specifications1

2.1 Performance Characteristics

Table 2-1: Performance Characteristics

2.2 Electrical Characteristics

Table 2-2: Absolute Maximum Ratings

CAUTION:

Stresses beyond those listed above may cause permanent damage to the device. These are stress ratings only. Operation of the device at these or other conditions beyond those indicated in the operational sections of the specifications is not implied.

Footnote

1. Specifications subject to change.

PNI Sensor Corporation Doc #1018049 R03 SENtral Technical Data Sheet Page 6

Parameter

Symbol

Min

Typical

Max

Units

Supply Voltage

VDD

1.6 3.3

VDC

Power-On Reset Threshold, V

REG>VPOR

POR

REG

– 0.125

VDC

High Level Input Voltage

VIH

0.7*VDD

VDD

VDC

Low Level Input Voltage

VIL 0

0.3*VDD

VDC

High Level Output Current, VOH = VDD – 0.3V

IOH

-1

Low Level Output Current, VOL = 0.3V

IOL 1

Current Consumption @

1.8 VDD Normal Operation1

100 – 300

µA

Pass-Through State2

µA

Standby State

µA

I2C Interface Data Rate3 Host Bus

3400

kbits/sec

Sensor Bus

1000

kbits/sec

Pass-Through

400

kbits/sec

Decoupling Capacitor (ESR <2)

reg

0.33

0.5

1.8

µF

Operating Temperature

TOP

-40

+25

+85

Table 2-3: Operating Conditions

Footnotes:

1. SENtral’s current consumption in normal operation is dependent on a number of variables, including the sensor update rates and the I2C sensor bus rate. The range given will be typical for most customers. There is a trade-off between sensor update rates and current consumption, as more frequent sensor update rates result in improved motion-tracking performance, while less frequent sensor update rates result in reduced current consumption. Faster I2C sensor bus rates result in lower current consumption.

2. Pass-Through current consumption assumes SENtral previously was in Standby State, which is recommended, and a sensor bus rate of 400 kbits/s (Fast mode).

3. SENtral’s I2C Host Interface supports Standard, Fast, Fast Plus, and High Speed Modes. High Speed Mode (3400 kHz) is supported with a reduced range of VDD and bus capacitance. SENtral’s I2C sensor bus interface supports Standard, Fast, and Fast Plus Modes. Pass-Through State, which connects the sensor bus and host bus, supports Standard and Fast Modes.

PNI Sensor Corporation Doc #1018049 R03 SENtral Technical Data Sheet Page 7

3 Layout

3.1 System Layout

Figure 3-1 provides a basic reference schematic for connecting SENtral with the host system and the various sensors.

Figure 3-1: SENtral System Reference Schematic

A few points on system layout.

 SENtral communicates with the sensors as the master via a dedicated I2C sensor bus.

The layout shows a discrete magnetometer, accelerometer, and gyroscope. SENtral also works with combo sensors, such as a single 9-axis sensor or a combo gyro/accel with a discrete magnetometer.

 SENtral acts as a slave on the host system’s I2C bus. This does not need to be a

dedicated bus, although it is shown this way in the schematic. SA0 establishes SENtral’s slave address when communicating with the host. It is shown set to ground, but can be set HIGH instead. See Section 4.2.

 The pull-up resistance on the I2C lines depends on the number of devices on the bus

and the bus speed. Normally 4.7 kΩ is appropriate for Standard or Fast modes (≤400 kbit/sec). See Section 4.4.

 There are three dedicated sensor interrupt lines between the sensors and SENtral, and

one interrupt line between the host and SENtral. The default GPIO assignments are shown, but these can be altered with the SENtral Configuration Tool. See Section 6.

PNI Sensor Corporation Doc #1018049 R03 SENtral Technical Data Sheet Page 8

Pin#

Pin Name

I/O Type*

Description

VDD

PWR

Supply voltage

VCAP

PWR

External compensation capacitor for internal core

voltage regulator

GND

PWR

Ground

SA0

I2C slave address bit [0]

SCLS

I2C host bus SCL clock line

SDAS

I2C host bus SDA data line

SCLM

I2C sensor bus SCL clock line

SDAM

I2C sensor bus SDA data line

GPIO[0]

IO / PUPD

General Purpose IO – Default mag interrupt

GPIO[1]

IO / PUPD

General Purpose IO – Default accel interrupt

GPIO[2]

IO / PUPD

General Purpose IO – Default gyro interrupt

GPIO[3]

IO / PUPD

General Purpose IO – Default not connected

GPIO[4]

IO / PUPD

General Purpose IO – Default not connected

GPIO[5]

IO / PUPD

General Purpose IO – Default not connected

GPIO[6]

IO / PUPD

General Purpose IO – Default host interrupt

RES

Not Used – Connect to Ground

3.2 Pin Assignments

SENtral’s pin-out is a 4x4 ball-grid array, as defined in Figure 7-1. The table below provides the pin assignments.

Table 3-1: SENtral Pin Assignments

*I/O Types are:

PWR: Power supply Connections I: Digital Input IO: Digital Input / Output PU: Pull-Up PD: Pull-Down

PNI Sensor Corporation Doc #1018049 R03 SENtral Technical Data Sheet Page 9

3.3 Sensor Layout

SENtral provides for considerable flexibility in sensor orientation and layout, but there are some basic requirements, as given below.

 All three axes of a sensor must be orthogonal to each other. This is by-design for

most accelerometers, gyroscopes, and magnetometers.

 A sensor’s X axis and Y axis should act parallel to the primary plane of the

motherboard. A sensor’s Z axis should act perpendicular to the primary plane.

 Either a sensor’s X axis or Y axis should align parallel to the line-of-sight of the

motion-tracking device.

 It is NOT necessary that the gyroscope, accelerometer, and magnetometer have their

same-axis sensors (i.e. all X-axis sensors) point in the same direction, since sensor orientation is configured when running the SENtral Configuration Tool and stored in the SENtral Configuration File.

Assuming the Orientation Matrix is properly input in the SENtral Configuration Tool, SENtral will output data conforming to a North-East-Down (NED) convention. To convert to East-North-Up (ENU) see Appendix II – Converting Quaternions.

In addition to the requirements listed above, other recommendations regarding sensor layout are given below. These represent good practices, but are not mandatory.

 Accelerometer

o Locate the accelerometer near the expected center of rotation of the device to

minimize rotational accelerations being interpreted as linear accelerations.

 Magnetometer

o Locate the magnetometer >1 cm away from magnetic sources (hard-iron), such as

speaker magnets or known magnetized metals. If uncertain about whether a component is a magnetic source, check it with a Gauss meter if possible.

o For non-magnetic components, try to avoid placing wireless antenna, power

capacitors, inductors, ferrite beads, and components using ferromagnetic materials (Fe, Co, Ni) within 1 cm of the magnetometer. Examples of components in a cell phone which typically contain ferromagnetic materials are the memory card slot, battery, frame, electrical and magnetic noise shields, connectors, and hinges.

o Materials that are magnetically transparent, and thus relatively safe, include

aluminum, gold, titanium, copper, brass, and magnesium. Most stainless steel alloys have relatively weak magnetic properties and are not as safe as those just listed, but don’t need as much attention as ferromagnetic materials.

o Locate high-frequency signal lines away from the magnetometer. o Locate power lines away from the magnetometer, per the table below.

PNI Sensor Corporation Doc #1018049 R03 SENtral Technical Data Sheet Page 10

Current (mA)

Recommended

Distance (mm)

0.2

10 1 50 5 100

200

Table 3-2: Recommended Power Line Distance from Magnetometer

3.4 Dedicated EEPROM (Optional)

A crucial step in using the SENtral coprocessor is uploading the SENtral Configuration File into SENtral’s RAM. This file contains information on how the sensor system is configured

in the user’s system, and is generated with the SENtral Configuration Tool, as discussed in

Section 6. The Configuration File can be manually uploaded from non-volatile memory in the host CPU or automatically uploaded from a dedicated EEPROM. The primary advantages of using a dedicated EEPROM are freeing up host processor memory and minimizing the time from power-up until the upload is complete. The advantages of using host CPU memory are no additional cost and no additional system footprint requirement.

If implementing a dedicated EEPROM, connect it to SENtral as a slave device on the sensor bus, in parallel with the sensors shown in Figure 3-1. The EEPROM upload rate should be set with the SENtral Configuration Tool (see Section 6.1.3). Faster is generally better, although the sensor bus rate is limited to 1 Mb/sec. Writing the Configuration File onto the EEPROM can be accomplished either using an EEPROM programmer or by writing to the EEPROM from the host while SENtral is in Pass-Through State.

The primary EEPROM requirements are:

 ≥320 Kbit (40 Kb x 8 bits) of memory.  Shifted address of 0xA0, 0xA2, 0xA4, 0xA6, 0xA8, or 0xAA. (Unshifted address of

0x50, 0x52, 0x54, 0x56, 0x58, or 0x5A.)

The following devices have been used with SENtral, but this list is not exhaustive.

 Microchip 24LC256T-I/SN  ST M24M01-DRCS  Renesas R1EX24512ASAS0A

PNI Sensor Corporation Doc #1018049 R03 SENtral Technical Data Sheet Page 11

4 I2C Interface

Communication with the host processor and sensors is via an I2C interface and interrupt lines. The SENtral Motion Coprocessor acts as the I2C master with the sensors and as a slave with the host processor. The sensor interrupt lines let SENtral know when new data is available, while the host interrupt line lets the host system know when SENtral has updated the quaternions. The sensor and host output data rates are set by the MagRate, AccelRate, GyroRate, and QRateDivisor registers.

SENtral’s I2C interface complies with NXP’s UM10204 specification and user manual, rev 04. Standard, Fast, Fast Plus, and High Speed modes of the I2C protocol are supported by SENtral’s I2C host interface. Below is a link to this document.

http://www.nxp.com/documents/user_manual/UM10204.pdf

4.1 I2C Timing

SENtral’s I2C timing requirements are set forth below, in Figure 4-1 and Table 4-1. For the timing requirements shown in Figure 4-1, transitions are 30% and 70% of VDD.

Figure 4-1: I2C Timing Diagram

PNI Sensor Corporation Doc #1018049 R03 SENtral Technical Data Sheet Page 12

Standard

Fast

Fast Plus

Units

Symbol

Parameter

Min

Max

Min

Max

Min

Max

SCL

SCL Clock

100 0 400

1000

kHz

SDA & SCL Rise

Time

1000

300 120

SDA & SCL Fall Time

300

20*(VDD/

5.5V)

300

20*(VDD/

5.5V)

120

LOW

LOW period of SCL

Clock

4.7 - 1.3 - 0.5

s

HIGH

HIGH period of SCL

Clock

4.0 - 0.6 - 0.26

s

HD;STA

Hold time (repeated)

START

4.0 - 0.6 - 0.26

s

HD;DAT

Data hold time

0 - 0 - 0

s

SU:DAT

Data set-up time

250 - 100 - 50 - ns

SU;STA

Set-Up time for

repeated Start

4.7 - 0.6 - 0.26

s

SU;STO

Stop set-up time

4.0 - 0.6 - 0.26

s

BUF

Bus free time between

STOP & START

4.7 - 1.3 - 0.5

s

Table 4-1: I2C Timing Parameters

4.2 I2C Host Interface (Host Bus)

The host will control SENtral on the host bus via SENtral’s I2C host interface. The host interface consists of 2 wires: the serial clock, SCLS, and the serial data line, SDAS. Both lines are bi-directional. SENtral is connected to the host bus via the SDAS and SCLS pins, which incorporate open drain drivers within the device. The host bus lines must be externally connected to a positive supply voltage (DVIO) via a pull-up resistor. See Section

4.4 for more on the pull-up resistor.

SENtral’s 7-bit I2C slave address is 0b010100x, where the most significant 6 bits of the slave address are pre-defined in hardware and are the same for all SENtral devices. The least significant bit is user-configurable, using the SA0 pin to set the bit to ‘0’ or ‘1’. For example, grounding the SA0 pin (‘0’ value) results in the 7-bit address of 0b0101000. This should be set so the SENtral slave address is unique to any other devices on the host bus. Note that setting SA0 to ‘1’ requires utilizing microvia technology, as discussed in Section 8.

PNI Sensor Corporation Doc #1018049 R03 SENtral Technical Data Sheet Page 13

START

SLAVE ADDRESS

ACK

DATA TO REGISTER (N)

ACK

DATA TO REGISTER (N+1)

ACK

STOP

A0 0 0

R0 0 D7

D0 0 D7

D0 0 P

From Host to SENtral

------------ Data Transferred (n bytes + acknowledge) ------------

From SENtral to Host

START

SLAVE ADDRESS

ACK

START

SLAVE ADDRESS

ACK

DATA FROM REGISTER (N)

NACK

STOP

A0 0 0

R0 0 SR

A0 1 0

D0 1 P

Data Transferred

(n bytes + acknowledge)

START

SLAVE ADDRESS

ACK

STOP

A0 0 0

R0 0 P

START

SLAVE ADDRESS

ACK

DATA FROM REG. (N)

ACK

DATA FROM REG. (N+1)

NACK

STOP

A0 1 0

D0 0 D7

D0 1 P

From Host to SENtral

-------------- Data Transferred (n bytes + acknowledge) --------------

From SENtral to Host

Data transfer is always initiated by the host. Data is transferred between the host and SENtral serially through the data line (SDAS) in an 8-bit transfer format. The transfer is synchronized by the serial clock line, SCLS. Supported transfer formats are single-byte read, multiple-byte read, single-byte write, and multiple-byte write. The data line can be driven either by the host or SENtral. Normally the serial clock line will be driven by the host, although exceptions can exist when clock-stretching is implemented in Pass-Through State.

4.2.1 I2C Slave Transfer formats

Figure 4-2 illustrates writing data to registers in single-byte or multiple-byte mode.

Figure 4-2: I2C Slave Write Example

The I2C host interface supports both a read sequence using repeated START conditions, shown in Figure 4-3, and a sequence in which the register address is sent in a separate sequence than the data, shown in Figure 4-4 and Figure 4-5.

Figure 4-3: I2C Slave Read Example, with Repeated START

Figure 4-4: I2C Slave Write Register Address Only

Figure 4-5: I2C Slave read register from current address

PNI Sensor Corporation Doc #1018049 R03 SENtral Technical Data Sheet Page 14

I2C Mode

Rate

(kbit/s)

Rise Time

(ns)

Max Cb (pF)

4.7 kΩ pull-up

2.4 kΩ pull-up

Standard

100

1000

251.1

491.8

Fast

400

300

75.3

147.5

Fast Plus

1000

120

30.1

59.0

High Speed-1.7 MHz

Clock

1700

20.1

39.3

Data

1700

160

40.2

78.7

High Speed-3.4 MHz

Clock

3400

10.0

19.7

Data

3400

20.1

39.3

4.3 I2C Sensor Interface (Sensor Bus)

SENtral communicates with the accelerometer, gyroscope, and magnetometer over the sensor bus, where SENtral acts as the I2C master and the sensors act as the I2C slaves. On the sensor bus, SENtral initiates data transfer and generates the serial clock. SENtral’s I2C sensor interface supports Standard mode with a rate up to 100 kbit/s, Fast mode with a rate up to 400 kbit/s, and Fast Plus mode with a rate up to 1000 kbit/s.

The two wires comprising the sensor bus are SDAM, the serial data line, and SCLM, the serial clock. Both are bidirectional and driven by open drain transistors within SENtral. Each line should be attached to a pull-up resistor, which is further discussed in Section 4.4.

4.4 I2C Pull-Up Resistance

The pull-up resistor value for both the host and sensor bus will depend on the I2C data rate and the number of devices on the bus. Table 4-2 provides the maximum acceptable bus capacitance, as a function of bus rate, which can be accommodated with a 4.7 kΩ or 2.4 kΩ pull-up resistor. As a general rule, each device connected to the bus represents 10 pF of capacitance on the bus, so a bus with 4 devices would require a “Max Cb” value of >40 pF.

Table 4-2: I2C Pull-Up Resistance Table

As the table implies, for most Standard and Fast Mode implementations a 4.7 kΩ pull-up should work well, while a 2.4 kΩ pull-up normally should be used for Fast Plus. See Section

7.1 of NXP’s UM10204 specification for additional information.

http://www.nxp.com/documents/user_manual/UM10204.pdf.

PNI Sensor Corporation Doc #1018049 R03 SENtral Technical Data Sheet Page 15

5 Operation

Figure 5-1 provides a flow chart of the initialization process, and a detailed discussion of the initialization process follows in Section 5.1. For the registers, all multi-byte elements are

stored and transmitted using the Little Endian convention: the least significant byte is stored at the lowest address and transmitted first over the I2C bus.

Figure 5-1: SENtral Initialization Sequence

PNI Sensor Corporation Doc #1018049 R03 SENtral Technical Data Sheet Page 16

+ 37 hidden pages

PNI SENtral User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

1 Product Overview

1.1 SENtral Features and Benefits

1.2 SENtral Functional Description

2 SENtral Specifications1

2.1 Performance Characteristics

2.2 Electrical Characteristics

3 Layout

3.1 System Layout

3.2 Pin Assignments

3.3 Sensor Layout

3.4 Dedicated EEPROM (Optional)

4 I2C Interface

4.1 I2C Timing

4.2 I2C Host Interface (Host Bus)

4.2.1 I2C Slave Transfer formats

4.3 I2C Sensor Interface (Sensor Bus)

4.4 I2C Pull-Up Resistance

5 Operation