Sensor networks in theory and practice: Successfully realize embedded systems projects

Preface
Preface to the Second Edition
Contents
1: Introduction
	1.1 What Do You Find in This Book?
	1.2 For Whom Is This Book Written?
	1.3 What Knowledge Does the Book Presuppose?
	1.4 Why Does the Book Not Describe an Arduino?
	1.5 Additional Materials
	1.6 Disclaimer
	1.7 Thanks
	References
2: Introduction to the Programming Language C
	2.1 The C Language: Background and Structure
		Example
	2.2 Identifiers, Keywords and Symbols in C
		2.2.1 Identifier
		2.2.2 Keywords
		2.2.3 Symbols
		2.2.4 Instructions
			Example
	2.3 Comments
		2.3.1 Single-Line Comment
		2.3.2 Multiline Comment
		2.3.3 Doxygen Comments
	2.4 Types, Variables and Constants
		2.4.1 Fundamental Data Types
		2.4.2 Declaration of Variables
			Examples
			Example
		2.4.3 Constants
	2.5 Operators
		2.5.1 Arithmetic Operators
		2.5.2 Logical Operators
		2.5.3 Bit Operators
		2.5.4 Operators for Memory Accesses
		2.5.5 Other Operators
		2.5.6 Associativity and Priority of Operators
		2.5.7 Type Conversion
	2.6 Control Structures
		2.6.1 Branches (Selection)
		2.6.2 Pitfalls
		2.6.3 Multiple Branching
	2.7 Loops
		2.7.1 Head Controlled Loops
		2.7.2 Foot-Controlled Loops
		2.7.3 Counting Loops
		2.7.4 Jumps
	2.8 Functions
		2.8.1 int main()
		2.8.2 Definition and Declaration
		2.8.3 Visibility and Lifetime of Variables in Functions
		2.8.4 Header
		2.8.5 The Keywords External, Volatile and Static
			Example
	2.9 Complex Data Types
		2.9.1 Arrays, Fields and Strings
		2.9.2 Structure
		2.9.3 Unions
		2.9.4 Enumeration Types
		2.9.5 Pointer
			2.9.5.1 Use in Function Calls
			2.9.5.2 Pointer Arithmetic
			2.9.5.3 Pointers to Functions
			2.9.5.4 Const Pointer
	2.10 Structure of an Embedded C Program
	2.11 Working with the Precompiler
		2.11.1 #define and Working with Macros
		2.11.2 #pragma
		2.11.3 Summary of the Precompiler Commands
	2.12 Translating and Binding
	References
3: Programming of AVR Microcontrollers
	3.1 Architecture of the AVR Family
	3.2 Packaging and Pin Assignments
	3.3 Supply, Clock and Reset Logic
		3.3.1 Supply
		3.3.2 Clock
		3.3.3 Reset Logic
		3.3.4 Memory
	3.4 Handling Registers
	3.5 Digital Input/Output
		3.5.1 Basic Structure
		3.5.2 Programming
	3.6 Interrupts
		3.6.1 Getting Started with Interrupts
		3.6.2 Interrupt Programming Using the Example of the Pin Change Interrupt
		3.6.3 The External Interrupts INTx
	3.7 Timer
		3.7.1 Timer Basics
		3.7.2 Programming the Timer/Counter
			3.7.2.1 Generation of a One Second Cycle
			3.7.2.2 Generation of a Fixed Frequency at an Output
			3.7.2.3 Output of a PWM Signal
			3.7.2.4 Debouncing the Keyboard with the Timer
			3.7.2.5 PWM for Advanced Users
			3.7.2.6 Continuous Timing Between Input Pulses
				3.7.2.6.1 Time Measurement in the Millisecond Range
				3.7.2.6.2 Measurement of the Phase of Two Sinusoidal Signals (Active and Reactive Power Measurement)
			3.7.2.7 Hardware Control of Motors with PWM Signals
	3.8 Analog Interface
		3.8.1 Analog Multiplexer
		3.8.2 Analog Comparator
		3.8.3 AD Converter (ADC)
			3.8.3.1 Functionality
			3.8.3.2 Triggering the Measurement
			3.8.3.3 Registers for AD Programming
			3.8.3.4 ADC Initialization
		3.8.4 Example: Thermometer
		3.8.5 Example: RMS Value Measurement on a Sinusoidal Voltage
	3.9 Power Management
	3.10 Internal EEPROM
		3.10.1 Declaration of a Variable in the EEPROM
		3.10.2 Reading from the EEPROM
		3.10.3 Writing to the EEPROM
	3.11 Dynamic Memory Use
	3.12 Moving Data to the Program Memory
	References
		Further Reading
4: Software Framework
	4.1 Views
	4.2 Hardware Abstraction
	4.3 Modularisation and Access to Modules
	4.4 Time Control
	References
5: Memory Concepts and Algorithms
	5.1 Important Storage Concepts
		5.1.1 Queues and Ring Buffers (FIFO)
		5.1.2 Queue with Dynamic Data Structures
		5.1.3 Multiple Queues in One Program
		5.1.4 Multiple Queues with Different Types
	5.2 State Machines
		5.2.1 General Consideration
		5.2.2 Description of State Machines
			Example
		5.2.3 Implementation of State Machines on Microcontrollers
	References
6: Theoretical Considerations for IoT Networks
	6.1 The ISO/OSI Layer Model
		6.1.1 Layer 1: Physical Layer
			6.1.1.1 Wires
			6.1.1.2 Transceiver
			6.1.1.3 Transmission Security
			6.1.1.4 Network Topologies
			6.1.1.5 Synchronization and Line Coding
		6.1.2 Layer 2: Data Link Layer
			6.1.2.1 Framing
			6.1.2.2 Media Access: MAC
			6.1.2.3 Communication Control
			6.1.2.4 Time Behaviour
			6.1.2.5 Error Handling
		6.1.3 Layer 3: Network Layer
		6.1.4 Layer 4: Transport Layer
		6.1.5 Application Protocols for IoT Networks
	6.2 Requirements for IoT Networks
	References
7: Asynchronous Serial Interfaces
	7.1 Universal Asynchronous Receiver/Transmitter (UART)
		7.1.1 Hardware Connection in the AVR Family
		7.1.2 UART Registers on the ATmega 88
		7.1.3 Initializing the UART Interface on the ATmega88
		7.1.4 Receiving Data
		7.1.5 Sending Data
		7.1.6 Implementation of UartWriteBuffer()
		7.1.7 UART Multiprocessor Mode
			7.1.7.1 Initialization of the Bus Devices in UART Multiprocessor Mode
			7.1.7.2 Receiving Data in UART Multiprocessor Mode
			7.1.7.3 Sending Frames in UART Multiprocessor Mode
	7.2 Connection of the Serial Interface to USB
	7.3 A Simple Serial Protocol
		7.3.1 Establishing Code Transparency by Bytestuffing
	References
8: Serial Peripheral Interface (SPI)
	8.1 Structure and Mode of Operation
	8.2 Configuration of the SPI Interface
		Example
	8.3 SPI Interface in Slave Mode
	8.4 SPI Interface in a Sensor Network
	8.5 3-Wire SPI Communication
	8.6 SPI Master Via USART
	Reference
9: The I2C/TWI Interface
	9.1 I2C-Bus Configuration
	9.2 Bus Extension
		9.2.1 I2C-Repeater
		9.2.2 I2C-Hub
		9.2.3 I2C Multiplexer
		9.2.4 I2C-Switch
	9.3 TWI in the AVR Family [5]
		9.3.1 TWI Register at the ATmega 88
		9.3.2 Initializing the TWI Interface
		9.3.3 TWI Communication
		9.3.4 The Microcontroller ATmega as TWI Master
			9.3.4.1 The TWI Master as Transmitter
			9.3.4.2 The TWI Master as Receiver
		9.3.5 The Microcontroller ATmega as TWI Slave
			9.3.5.1 The TWI Slave as Receiver
			9.3.5.2 The TWI Slave as Transmitter
	References
10: CAN Bus
	10.1 CAN Basics Compact
	10.2 CAN Timing
	10.3 Use of CAN with Processors of the AVR Family
		10.3.1 CAN Controller MCP2515
			10.3.1.1 Initialization
			10.3.1.2 Sending Messages
			10.3.1.3 Receiving Messages
		10.3.2 AT90CANxx
			10.3.2.1 Implementation on the AT90CANx
				10.3.2.1.1 Initialization
				10.3.2.1.2 Sending Messages
				10.3.2.1.3 Receiving Messages
		10.3.3 Implementation with the CAN Library of the Robot Club Aachen
	10.4 CAN Transport Protocol
	10.5 CANopen in Industrial Control Technology
	References
11: The Modbus
	11.1 TIA/EIA-485 as Physical Layer for MODBUS
	11.2 MODBUS Communication
		11.2.1 Remote Terminal Unit Transmission
		11.2.2 ASCII Transmission
	References
12: Single-Wire Bus Systems
	12.1 1-Wire-BUS
		12.1.1 Network Topology
		12.1.2 Initialization of the Bus
		12.1.3 1-Wire Bit Transmission
		12.1.4 Communication Session
			12.1.4.1 ROM Commands
				12.1.4.1.1 Search ROM (Code 0xF0)
				12.1.4.1.2 Read ROM (Code 0x33)
				12.1.4.1.3 Match ROM (Code 0x55)
				12.1.4.1.4 Skip ROM (Code 0xCC)
			12.1.4.2 Addressing
			12.1.4.3 Function Commands
		12.1.5 Software Structure of the 1-Wire Bus Communication
		12.1.6 Control of a 1-Wire Temperature Sensor of the Type DS18B20
			12.1.6.1 Memory Organization
			12.1.6.2 Temperature Coding
			12.1.6.3 Function Commands DS18B20
				12.1.6.3.1 Start Temperature Measurement (0x44)
				12.1.6.3.2 Write RAM (0x4E)
				12.1.6.3.3 Read RAM (0xBE)
	12.2 UNI/O Bus
		12.2.1 Network Topology
		12.2.2 Bit Coding
		12.2.3 UNI/O Frame
		12.2.4 Communication Session
			12.2.4.1 Initialization of Communication
			12.2.4.2 Addressing
			12.2.4.3 Function Commands
		12.2.5 Software Structure of UNI/O Bus Communication
		12.2.6 Control of a 11XXYZ-EEPROM
			12.2.6.1 Memory Write Protection of the 11XXYZ Devices
			12.2.6.2 Addressing the 11XXYZ-EEPROMs
			12.2.6.3 Function Commands of the 11 XXYYZ EEPROMs
				12.2.6.3.1 Commands that Trigger an Internal Action
				12.2.6.3.2 Commands Indicating an Implicit Address
				12.2.6.3.3 Commands that Refer to an Explicit Address
			12.2.6.4 Parasitic Supply of an 11XXYZ-EEPROM
	12.3 LIN Bus
	References
13: Wireless Networks
	13.1 Basics of the Radio Interfaces
		13.1.1 Multiplexing
		13.1.2 Sensor Nodes
	13.2 Radio Transmission in the 433 MHz and 868 MHz ISM Bands
		13.2.1 Structure of the RFM12B
		13.2.2 Wiring of the RFM12 Radio Module
		13.2.3 The SPI Communication
		13.2.4 The Instruction Set
		13.2.5 The Status Register
		13.2.6 Initialization of the Transceiver
		13.2.7 Send Data
		13.2.8 Reading the Received Data
	13.3 Radio Protocols in the 2.4 GHz ISM Band
		13.3.1 Bluetooth
			13.3.1.1 Physical Layer [12, 15]
			13.3.1.2 Communication Topologies
				13.3.1.2.1 BR/EDR Topologies
				13.3.1.2.2 LE Topologies [15]
			13.3.1.3 Establishing a Connection in a Piconet
				13.3.1.3.1 Establishing a Connection in a BR/EDR Piconet
				13.3.1.3.2 Establishing a Connection in a LE Piconet
			13.3.1.4 Security of Communication
		13.3.2 ZigBee
			13.3.2.1 ZigBee Devices
			13.3.2.2 Protocol Structure
			13.3.2.3 Physical Layer
			13.3.2.4 Network Layer
			13.3.2.5 ZigBee Device Object
			13.3.2.6 Application Framework
	13.4 Bluetooth Communication with the Serial Profile
		13.4.1 Operating Modes
		13.4.2 Command Set
			Example
		13.4.3 Initialization of the Radio Module
			13.4.3.1 Initialization of the Bluetooth Master
			13.4.3.2 Initialization of the Bluetooth Slave
	References
14: Sensor Technology System Considerations
	14.1 Sampling
	14.2 Quantization
	14.3 Digital Filtering
		14.3.1 Finite Impulse Response (FIR) Filter
		14.3.2 Infinite Impulse Response (IIR) Filter
		14.3.3 Filtering Using the Example of an FIR Filter
	14.4 I/O Control Logic
	14.5 Abstraction of the I/O Pins
	14.6 Integer Arithmetic
		14.6.1 Microcontroller Internal Number Formats
		14.6.2 Unsigned Integer Types
		14.6.3 Signed Integer Types
		14.6.4 Detection and Prevention of Overflow
	References
15: Environmental Sensors
	15.1 MPL3115 Digital Air Pressure Sensor
		15.1.1 Functionality
		15.1.2 Structure of the MPL3115
			15.1.2.1 Measuring Probe
			15.1.2.2 Register
				15.1.2.2.1 Control Register Block
				15.1.2.2.2 Status Registers
				15.1.2.2.3 Measured Value Registers
					15.1.2.2.3.1 Absolute Measured Values
					15.1.2.2.3.2 Relative Measured Values
					15.1.2.2.3.3 Extreme Values
					15.1.2.2.3.4 FIFO Registers
					15.1.2.2.3.5 Interrupt Registers
					15.1.2.2.3.6 Device Identification Registers
		15.1.3 Serial Communication
		15.1.4 Power Modes
		15.1.5 Measuring and Reading Modes
		15.1.6 Initialization of the MPL3115 Sensor
	15.2 Humidity Sensor SI7021
		15.2.1 Structure of the SI7021
		15.2.2 Serial Communication
			15.2.2.1 Access to the Control Register
			15.2.2.2 Measurement of Relative Humidity
			15.2.2.3 Measurement of Temperature
			15.2.2.4 Reading the Electronic ID and the Firmware Revision
		15.2.3 Calculation of Temperature and Relative Humidity
		15.2.4 Testability
	15.3 Temperature Measurement with the TMP75
		15.3.1 Sensor Configuration
		15.3.2 Serial Interface
		15.3.3 Temperature Measurement
		15.3.4 Thermostat Function
	15.4 Fine Dust Sensor SDS011
		15.4.1 Measuring Principle
		15.4.2 Control and Serial Communication
	References
16: Accelerometers
	16.1 Acceleration Sensor ADXL312
		16.1.1 Networking of the ADXL312
		16.1.2 Measurement Data Acquisition
			16.1.2.1 Initialization of the Sensor
			16.1.2.2 Working Mode
			16.1.2.3 Measurement Frequency Setting
			16.1.2.4 Measurement Data Format
			16.1.2.5 Saving Measurement Data
			16.1.2.6 Reading the Measured Values
		16.1.3 Offset Determination
		16.1.4 Interrupt Mode
		16.1.5 ADXL312 as Inclination Sensor
			16.1.5.1 Theoretical Approach
			16.1.5.2 Correction of the Measured Values
			16.1.5.3 Calculation of the Angle of Inclination and the Direction of Inclination
	16.2 MMA6525
		16.2.1 Sensor Structure
		16.2.2 Register Block
			16.2.2.1 OTP-Register
			16.2.2.2 Read-Write Registers
			16.2.2.3 Read-Only Registers
		16.2.3 SPI Communication
			16.2.3.1 Initialization of the Sensor
			16.2.3.2 Reading a Register
			16.2.3.3 Writing a Register
			16.2.3.4 Reading Out the Acceleration Values
	References
17: Angular Rate Sensors
	17.1 Gyroscope
		17.1.1 Wiring of the L3GD20
		17.1.2 Communication Interfaces
		17.1.3 Working Modes
			17.1.3.1 Angular Velocity Measurement
			17.1.3.2 Intermediate Storage of the Measured Values
				17.1.3.2.1 Direct Saving
				17.1.3.2.2 Buffered Storage
					17.1.3.2.2.1 Bypass Mode (FIFO_EN = 1 and FM2:0 = 000)
					17.1.3.2.2.2 FIFO Mode (FIFO_EN = 1 and FM2:0 = 001)
					17.1.3.2.2.3 Stream Mode (FIFO_EN = 1 and FM2:0 = 010)
			17.1.3.3 Reading Out the Measured Values
				17.1.3.3.1 Reading Out the Directly Stored Measured Values
				17.1.3.3.2 Reading Out the Buffered Measured Values
			17.1.3.4 Interrupt Control
				17.1.3.4.1 Threshold Setting for Interrupt 1
				17.1.3.4.2 Setting the Pulse Duration at Pin INT1
			17.1.3.5 Temperature Measurement
	References
18: Magnetic Field Sensors
	18.1 HMC5883 Magnetic Field Sensor
		18.1.1 Structure of the HMC5883
			18.1.1.1 Sensing Elements
			18.1.1.2 Control Logic
			18.1.1.3 Serial Communication
			18.1.1.4 Register Block
				18.1.1.4.1 Configuration Registers
				18.1.1.4.2 Measured Value Registers
				18.1.1.4.3 Status Register (Address 0x09)
				18.1.1.4.4 Identification Registers
		18.1.2 Reading HMC5883 Measured Values
			18.1.2.1 Reading Measured Values in Single Measurement Mode
			18.1.2.2 Reading Measured Values in Free-Running Measuring Mode
				18.1.2.2.1 Asynchronous Reading in Free-Running Mode
				18.1.2.2.2 Synchronous Reading in Free-Running Mode
		18.1.3 Calibration of the Sensor
			Example
		18.1.4 HMC5883 as Electronic Compass
		18.1.5 Angle Calculation with the CORDIC Algorithm
	References
19: Proximity Sensors
	19.1 Ultrasonic Proximity Sensors
		19.1.1 Measuring Principle
		19.1.2 SRF08: Ultrasonic Measuring Module
			19.1.2.1 Structure
			19.1.2.2 Serial Communication
			19.1.2.3 Measurement Value Acquisition
				19.1.2.3.1 Distance Measurement Mode
				19.1.2.3.2 Artificial Neural Network: Measurement Mode
				19.1.2.3.3 Light Brightness Measurement
	19.2 SI114x: Optical Proximity Sensor
		19.2.1 SI114x: Operating Modes
		19.2.2 SI114x: Structure
		19.2.3 Serial Communication
		19.2.4 Measurements with the SI114x
			19.2.4.1 Measuring Mode: Setting and Selection of the Measuring Channel
			19.2.4.2 Setting the Infrared Light Pulses
			19.2.4.3 Selection of the Measuring Sensor and the Measuring Settings
			19.2.4.4 Initialization of the Sensor
			19.2.4.5 Starting the Measurement
			19.2.4.6 Reading the Measured Values
		19.2.5 Interrupts
		19.2.6 SI114x: Network Identification
	References
20: Digital-to-Analog and Analog-to-Digital Converters
	20.1 MCP48XX SPI-Driven Digital-to-Analog Converters
		20.1.1 The SPI Interface
		20.1.2 The Input Register
		20.1.3 The D/A Converter
		20.1.4 The Analog Output Amplifier
		20.1.5 Synchronous Control of Two D/A Converters
		20.1.6 Software Example
	20.2 PCF8591 I2C-Controlled D/A and A/D Converter
		20.2.1 I2C Communication
		20.2.2 The D/A Converter
		20.2.3 The A/D Converter
		20.2.4 The Control Register
		20.2.5 The Oscillator
	20.3 Current Measurement with the LMP92064
		20.3.1 LMP92064 Structure
		20.3.2 Serial Communication
		20.3.3 Measuring with the LMP92064
			20.3.3.1 Voltage Measurement
			20.3.3.2 Current Measurement
	References
21: Serial EEPROMs
	21.1 Parallel Read-Only Memories
	21.2 Serial EEPROM Memory
		21.2.1 M24C64: I2C-Controlled EEPROM
			21.2.1.1 I2C Communication
			21.2.1.2 Reading
				21.2.1.2.1 Sequential Reading from the Current Address
				21.2.1.2.2 Sequential Reading with Direct Access
			21.2.1.3 Write
			21.2.1.4 Testability
		21.2.2 25LC256: SPI Controlled EEPROMs
			21.2.2.1 Write Protection of the Memory
			21.2.2.2 Read-Write Functions
			21.2.2.3 Memory Control
			21.2.2.4 Initialization of the SPI Interface of the Microcontroller
			21.2.2.5 Software Example
	References
22: Serial Flash Memory
	22.1 AT45DB161 Serial Flash Memory
		22.1.1 SPI Communication
		22.1.2 SRAM Buffer Memory
		22.1.3 Flash Main Memory
		22.1.4 Reading
			22.1.4.1 Reading from the Entire Memory Area
			22.1.4.2 Reading Within a Memory Page
			22.1.4.3 Loading a Memory Page Into a Buffer
		22.1.5 Write
			22.1.5.1 Write Buffer in Flash Page with Erase
			22.1.5.2 Write Buffer in Flash Page Without Erase
			22.1.5.3 Comparison Between Stored Page and Source Buffer
			22.1.5.4 Write Data Via Buffer in Flash Page with Erase
			22.1.5.5 Memory Write with Direct Access Via Buffer 1
		22.1.6 Erase
		22.1.7 Memory Protection
			22.1.7.1 Temporary Write Protection (Sector Protection)
			22.1.7.2 Permanent Write Protection (Sector Lockdown)
		22.1.8 Testability
			22.1.8.1 Status Registers
			22.1.8.2 Security Register (Security Register)
			22.1.8.3 Manufacturer and Chip ID Registers
	22.2 SST25WF0808 Serial Flash Memory
		22.2.1 SPI Communication
		22.2.2 Status Register
		22.2.3 Read Functions
		22.2.4 Erase Functions
		22.2.5 Write Functions
		22.2.6 2-Line Serial Interface
	References
23: Integrated Circuits for Audio Technology
	23.1 SI4840 Radio IC
		23.1.1 Module Description
		23.1.2 Selection of the Frequency Band and Frequency Tuning
		23.1.3 Initializing the Device
		23.1.4 Communication with the Device
			23.1.4.1 Power_Up Command
			23.1.4.2 Power_Down Command
			23.1.4.3 Get_Status Command
			23.1.4.4 Audio Mode Command
			23.1.4.5 Set_Property Command
			23.1.4.6 Get_Property Command
			23.1.4.7 Get_Rev Command
		23.1.5 Searching for Broadcast Stations with the SI4840
	23.2 LM48100Q Amplifier Module
	References
24: Networkable Integrated Circuits
	24.1 PCF8574: Port Expander
		24.1.1 Output Stage of an I/O Pin
		24.1.2 Output Port Mode
		24.1.3 Input Port Mode
		24.1.4 Interrupt Mode
		24.1.5 PCA9534
	24.2 MCP41X1 Digital Variable Resistors
		24.2.1 Power On/Brown Out Reset Circuitry
		24.2.2 Electrical Resistance
		24.2.3 Potentiometer Registers
		24.2.4 Control Functions of the MCP4151 Device
		24.2.5 SPI Communication
		24.2.6 Software Example
	24.3 MAX31629: Real Time Clock (RTC)
		24.3.1 Timing
		24.3.2 Alarm Time
		24.3.3 Temperature Measurement
		24.3.4 Thermostat with Alarm Function
		24.3.5 I2C Communication
	References
25: Displays
	25.1 Introduction
		25.1.1 Display Layout
		25.1.2 Emissive and Non-emissive Displays
			25.1.2.1 Liquid Crystal Displays (LCD)
			25.1.2.2 LED Indicators
		25.1.3 Image Composition
		25.1.4 Display Control
	25.2 Dot Matrix LCD Display with Parallel Control
		25.2.1 Structure of a Display with a KS0070B Controller
		25.2.2 Command Set
		25.2.3 4-Bit Communication
		25.2.4 Generation of a New Character
		25.2.5 Execution of the Display Commands Without Blocking Wait
	25.3 Serial Control of a Parallel LC Display
		25.3.1 Display Control Via I2C
		25.3.2 Software Example: Transmission of a Data Byte
	25.4 DOGS102-6: Graphic Display with Serial Control
		25.4.1 Structure of the Graphic Display DOGS 102-6
		25.4.2 SPI Communication
		25.4.3 Command Set
		25.4.4 Generation of a Character
	References
26: Example Projects
	26.1 Data Logger
		26.1.1 Structure of the Model Rocket
		26.1.2 Description of the Project
		26.1.3 Description of the Software
			26.1.3.1 The State Machine
			26.1.3.2 Logging on the Flash
			26.1.3.3 Read Out Data
		26.1.4 Evaluation
	26.2 Smart Home with CAN
		26.2.1 Structure
			26.2.1.1 Keyboard Block
	Reference