Communication protocols - Embedded Systems

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Information about Communication protocols - Embedded Systems

Published on March 5, 2014

Author: EmertxeSlides



Communication protocols in Embedded Systems. This presentation focused mainly on lower level protocols. Ideal for the beginner to build understanding on these protocols like I2C, USB, SPI etc.

Communication Protocols I Team Embedded Emertxe Information Technologies (P) Ltd Bangalore

Communication Protocols I Introduction SPI I2C CAN USB

Introduction What do mean by Communication? Mode of Communications Type of Communications Why Protocols?

Modes of Communication Simplex Half Duplex Duplex


Serial Peripheral Interface Introduction Interface Hardware Configurations Data Transmission Data Propagation Data Validity

SPI Introduction Synchronous Full Duplex Master / Slave


SPI Hardware Configuration

SPI Hardware Configuration

SPI Hardware Configuration

SPI Data Transmission

SPI Data Transmission

SPI Data Transmission

SPI Data Transmission

SPI Data Transmission

SPI Data Transmission

SPI Data Transmission

SPI Data Transmission

SPI Data Transmission

SPI Data Validity

Inter Integrated Circuits Introduction to I²C I²C Bus Features The I²C Bus Protocol Bus Speeds

2 IC Introduction Synchronous Half Duplex Multi Master / Slave

2 IC Bus Features Two Line Interface Software Addressable Multi Master with CD Serial, 8 bit Oriented, Bidirectional with 4 Modes On Chip Filtering

2 IC Protocol Example Signals A Complete Data Transfer

2 IC Example

2 IC Signals Two-wired Interface SDA SCL Wired-AND Conditions and Data Validity Transmission

2 IC Signals – Wired-AND

2 IC Signals – Conditions and Data Validity

2 IC Signals – Transmission Data on SDA Clocking on SCL Clock Synchronization Data Arbitration

2 IC Signals – Data on SDA

2 IC Signals – Data on SDA

2 IC Signals – Data on SDA

2 IC Signals – Data on SDA

2 IC Signals – Data on SDA

2 IC Signals – Clocking on SCL

2 IC Signals – Clock Synchronization

2 IC Signals – Data Arbitration

2 IC A Complete Data Transfer

2 IC Bus Speeds Bidirectional Bus Standard Mode - 100 Kbit/s Fast Mode - 400 Kbits/s Fast Mode Plus - 1 Mbits/s High Speed Mode - 3.4 Mbits/s Unidirectional Bus Ultra Fast Mode – 5 Mbits/s Uses Push-Pull Drivers (No Pullups)

Controller Area Network Introduction to CAN Basic Concepts Message Transfer Message Filtering Message Validation Coding Error Handling Fault Confinement Oscillator Tolerance Bit Timing Requirement

CAN Introduction Asynchronous Half Duplex Multi Master / Slave

CAN Basic Concepts Example Versions Absence of node addressing Message identifier specifies contents and priority Lowest message identifier has highest priority Non-destructive arbitration system by CSMA with collision detection Simple Transmission Medium Twisted pair – CAN H and CAN L Properties Layered Architecture

CAN Basic Concepts - Example

CAN Basic Concepts - Versions NOMENCLATURE STANDARD MAX. SIGNALING RATE IDENTIFIER Low Speed CAN ISO 11519 125 kbps 11 bit CAN 2.0A ISO 11898:1993 1 Mbps 11 bit CAN 2.0B ISO 11898:1995 1 Mbps 29 bit

CAN Basic Concepts - Properties Prioritization of Messages Guarantee of Latency Times Configuration of Flexibility Multicast Reception with Time Synchronization System wide Data Consistency Multi master Error Detection and Error Signalling Automatic Retransmission Distinction between temporary errors and permanent failures of nodes and autonomous switching off of defect nodes

CAN Basic Concepts - Layered Architecture

CAN Basic Concepts - Layered Architecture

CAN Basic Concepts - Layered Architecture

CAN Message Transfer Frame Formats Standard Frame - 11 bits Identifiers Extended Frame - 29 bits Identifiers Frame Types Data Frame Remote Frame Error Frame Overload Frame Frame Fields

CAN Message Transfer - Frame Formats

CAN Message Transfer – Data Frame A data frame consists of seven fields: start-of-frame, arbitration, control, data, CRC, ACK, and end-of-frame.

CAN Message Transfer – Remote Frame Used by a node to request other nodes to send certain type of messages Has six fields as shown in above figure These fields are identical to those of a data frame with the exception that the RTR bit in the arbitration field is recessive in the remote frame.

CAN Message Transfer – Error Frame This frame consists of two fields. The first field is given by the superposition of error flags contributed from different nodes. The second field is the error delimiter. Error flag can be either active-error flag or passive-error flag. Active error flag consists of six consecutive dominant bits. Passive error flag consists of six consecutive recessive bits. The error delimiter consists of eight recessive bits.

CAN Message Transfer – Overload Frame Consists of two bit fields: overload flag and overload delimiter Three different overload conditions lead to the transmission of the overload frame: Internal conditions of a receiver require a delay of the next data frame or remote frame. At least one node detects a dominant bit during intermission. A CAN node samples a dominant bit at the eighth bit (i.e., the last bit) of an error delimiter or overload delimiter. Format of the overload frame is shown in above fig The overload flag consists of six dominant bits. The overload delimiter consists of eight recessive bits.

CAN Message Transfer – Frame Fields Control Field Arbitration Field Data Field CRC Field ACK Field

CAN Frame Fields – Control Field The first bit is IDE bit for the standard format but is used as reserved bit r1 in extended format. r0 is reserved bit. DLC3…DLC0 stands for data length and can be from 0000 (0) to 1000 (8).

CAN Frame Fields – Arbitration Field The identifier of the standard format corresponds to the base ID in the extended format. The RTR bit is the remote transmission request and must be 0 in a data frame. The SRR bit is the substitute remote request and is recessive. The IDE field indicates whether the identifier is extended and should be recessive in the extended format. The extended format also contains the 18-bit extended identifier.

CAN Frame Fields – Data Field May contain 0 to 8 bytes of data

CAN Frame Fields – CRC Field It contains the 16-bit CRC sequence including CRC delimiter. The CRC delimiter is a single recessive bit.

CAN Frame Fields – Ack Field Consists of two bits The first bit is the acknowledgement bit. This bit is set to recessive by the transmitter, but will be reset to dominant if a receiver acknowledges the data frame. The second bit is the ACK delimiter and is recessive.

CAN Error Handling Error Detection Bit Error Stuff Error CRC Error Form Error Acknowledgement Error Error Signalling

CAN Fault Confinement Counters Transmit Error Counter & Receive Error Counter

CAN Error Handling Error Detection Bit Error Stuff Error CRC Error Form Error Acknowledgement Error Error Signalling

Universal Serial Bus Introduction Technical Overview Interfaces Architecture Communication Overview Extensions OTG Wireless

USB Introduction Asynchronous Half Duplex Master / Slave Offers simple connectivity Low cost Ease of use Manages power efficiently Supports all kinds of Data

USB Technical Overview Upstream Connection and Downstream Connection Uses three types of cables and two types of connectors High Speed cables at 480 Mbps Full Speed cables at 12 Mbps and Low Speed cables at 1.5 Mbps

USB Interfaces Differential Connection D+ D- Upstream Connection and Downstream Connection Physical Connection Type A Connector Type B Connector

USB Architecture Follows a Tiered star Topology and consists of: Peripherals Hubs Host controller Peripherals receive and respond to the commands from the host. E.g. Mice, Keyboard, Joysticks Two types of Peripherals Standalone Compound Device

USB Bus Topology Connection model between USB devices and the host.

USB Architecture Host recognizes the peripheral through a process called Enumerations Host communicates with the peripheral to learn its identity and identifies which device driver is required Host supplies the peripheral with an address Host is the controller of the entire network. e.g. PC Hubs: Allows many USB devices to share a single USB port USB devices with some incorporated intelligence Increase the logical and physical fan out

USB Architecture Single upstream connection and one-many down stream connection Smart wire passing data between the peripheral and Host Direct connection exists between host and peripherals Two kinds of Hubs: Bus Powered Hub: Draws power from the host computers USB interface Self Powered Hub: Has a built in power supply.

USB Power Management Peripherals connected regardless of the power state A pair of wires to supply power to the peripherals Manage power by enabling and disabling power to devices Removes electrically ill behaved systems from the network

USB Communication Overview End point is a unique point in the device which is the source or the receiver of the data End point has a definite address associated with it Codes indicate the type of transfer 16 end points within each device each end point has a 4 bit address End point “0” reserved for control transfers

USB Communication Overview Transactions between the host and end point take place through virtual pipes Pipes are logical channels which connect the host to the end points Once the communication is established the end points return a descriptor Descriptor is a data structure tells the host about the end points configuration and expectations

USB Communication Overview USB supports four transfer types of data: Control Transfers: Exchange information such as configuration, command information , set up between host and end point Bulk Transfers: Supports bulk amounts of data when timely delivery isn’t critical. e.g. Printers and Scanners Isochronous transfers: Handle transfers like streaming data Interrupt transfers: Poll devices to see if they need service

USB Extensions USB 2.0 PictBridge Standard to communicate imaging devices Microsoft X box console IBM Ultraport USB 1.0 OTG USB 1.0a supplement OTG Wireless USB

USB OTG USB On-The-Go Technology is used to provide dual role to the peripherals Enables direct communication between the hosts without involving the processor Incorporates Mini A , Mini B, Mini AB plugs and receptacles Highly complex design

USB OTG Advantages: Provides Dual Role Devices Introduces new connector types, Mini A, Mini B, Mini AB Provides with Aggressive Power Management On the Go Functionality of the USB can be implemented: Using a Full solution Approach Using a USB microcontroller Designing a custom IC

USB Wireless A Paradigm developed by Cypress that allows devices to be connected but appear as if they are connected to the host over normal USB connectivity Addresses many of the Design issues of Wireless networking An evolution that relies on familiar and existing technologies Desirable for point to point devices Features of Wireless USB are its Ease of use, simple connectivity and conservation of the battery power

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