Lantronix DSTni-EX manual CANBUS Background, Data Exchanges and Communication

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CANBUS Background

CAN is a fast and highly reliable, multicast/multimaster, prioritized serial communications protocol that is designed to provide reliable and cost-effective links. CAN uses a twisted-pair cable to communicate at speeds of up to 1 MB/s with up to 127 nodes. It was originally developed to simplify wiring in automobiles. Today, it is often used in automotive and industrial- control applications.

Data Exchanges and Communication

A CAN message contains an identifier field, a data field and error, acknowledgement, and cyclic Redundancy check (CRC) fields.

The identifier field consists of 11 bits for CAN 2.0A or 29 bits for CAN 2.0B. The size of the data field is variable, from zero to 8 bytes.

When data transmits over a CAN network, no individual nodes are addressed. Instead, the message is assigned an identifier that uniquely identifies its data content.

The identifier defines not only the message content, but also the message priority. Any node can access the bus. After successful arbitration by one node, all other nodes on the bus become receivers. After receiving the message correctly, these nodes perform an acceptance test to determine if the data is relevant to that particular node. Therefore, it is not only possible to perform communication on a peer-to-peer basis, where a single node accepts the message; it is also possible to perform broadcast and synchronized communications, whereby multiple nodes can accept the same message that is sent in a single transmission.

Arbitration and Error Checking

CAN employs the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) mechanism to arbitrate access to the bus. Unlike other bus systems, CAN does not use acknowledgement messages, which cost bandwidth on the bus. All nodes check each frame for errors. Any node in the system that detects an error immediately signals this to the transmitter. By having all nodes check for errors in transmitted frames, CAN provides high network data security.

CANBUS error checking includes:

CRC errors Acknowledgement errors Frame errors

Bit errors

Bit stuffing errors

The concept of bit stuffing involves inserting a bit of opposite polarity when more than five consecutive bits have the same polarity. If an error is detected by any of the other nodes, regardless of whether the message was meant for it or not, the current transmission aborts by transmission of an active error frame. An active error frame consists of six consecutive dominant bits and prevents other nodes from accepting the erroneous message. The active error frame violates bit stuffing and can also corrupt the fixed form of the frame, causing other nodes to transmit their own active error frames. After an active error frame, the transmitting node retransmits the frame automatically within a fixed period of time.

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Contents DSTni-EX User Guide Section FivePage Copyright & Trademark LantronixTechnical Support Master DistributorWarranty Contents 1 About This User Guide2 SPI Controller 3 I2C ControllerList of Tables 5 CAN ControllersTable 3-17. Clock Control Register List of Figures 1 About This User Guide Intended Audience ConventionsNavigating Online Notes Notes are information requiring attentionOrganization 2 SPI Controller Theory of OperationSPI Background DSTni SPI ControllerSPI Controller Register Summary Table 2-1. SPI Controller Register SummarySPI Controller Register Definitions SPIDATA RegisterRESET Table 2-2. SPIDATA RegisterCTL Register Interrupt Request EnablePhase Select Wire-OSPISTAT Register Table 2-6. SPISTAT RegisterTable 2-7. SPISTAT Register Definitions Interrupt RequestSPISSEL Register Table 2-10. BCNT Bit SettingsSelectO Signal Table 2-8. SPISSEL RegisterDVDCNTRLO Register DVDCNTRHITable 2-11. DVDCNTRLO Register Table 2-12. DVDCNTRLO Register DefinitionsFeatures 3 I2C ControllerI2C Background Block DiagramFigure 3-1. DSTni I2C Controller Block Diagram Operating Modes I2C ControllerMaster Transmit Mode Table 3-1. Master Transmit Status Codes CodeI2C State Microprocessor ResponseServicing the Interrupt Table 3-2. Codes After Servicing Interrupts Master TransmitTransmitting Each Data Byte Table 3-3. Status Codes After Each Data Byte TransmitsAll Bytes Transmit Completely Master Receive ModeTable 3-4. Master Receive Status Codes Table 3-5. Codes After Servicing Interrupt Master Receive Table 3-6. Codes After Receiving Each Data Byte Receiving Each Data ByteSlave Transmit Mode Slave Receive Mode Bus Clock Considerations Bus Clock SpeedClock Synchronization Bus ArbitrationProgrammer’s Reference I2C Controller Register SummaryResetting the I2C Controller Table 3-7. I 2C Controller Register SummaryI2C Controller Register Definitions Slave Address RegisterGeneral Call Address Enable Table 3-8. Slave Address RegisterData Register Table 3-10. Data RegisterControl Register Table 3-12. Control RegisterTable 3-13. Control Register Definitions Extended Slave AddressStatus Register Table 3-14. Status RegisterTable 3-16. Status Codes Table 3-15. Status Register DefinitionsStatus Code Table 3-17. Clock Control Register Clock Control RegisterTable 3-18. Clock Control Register Definitions Software Reset Register Extended Slave Address RegisterTable 3-21. Software Reset Register Table 3-22. Software Reset Register Definitions4 USB Controller USB Background USB InterruptUSB Core Serial Interface EngineUSB Hardware/Software Interface Digital Phase Lock Loop LogicMicroprocessor Interface Buffer Descriptor TableFigure 4-1. Buffer Descriptor Table Rx vs. Tx as a Target Device or HostTable 4-1. USB Data Direction Addressing BDT EntriesTable 4-2. 16-Bit USB Address Table 4-3. 16-Bit USB Address DefinitionsTable 4-4. BDT Data Used by USB Controller and Microprocessor USB Controller Determines…Microprocessor Determines… Table 4-5. USB Buffer Descriptor FormatTable 4-6. USB Buffer Descriptor Format Definitions BD OwnerDATA0/1 Transmit or Receive USB OwnershipUSB Transaction Figure 4-2. USB Token TransactionTable 4-7. USB Register Summary USB Register SummaryDedicated to host mode USB Register Definitions Interrupt Status RegisterTable 4-8. Interrupt Status Register Table 4-9. 16- Interrupt Status Register DefinitionsEnable/Disable USBRST Interrupt Sleep TimerError Condition USB ResetTable 4-10. Error Interrupt Status Register Error RegisterTable 4-11. 16- Error Interrupt Status Register Definitions Error interrupt with two functions Data Field Received Not 8 BitsCRC16 Failure PID check field failedLive USB Differential Receiver JSTATE Signal Live USB Single Ended Zero SignalTable 4-12. Status Register Table 4-13. Status Register DefinitionsUSB Reset Signal Host Mode Enable valid for host mode onlyResume Signaling BDT PDD ResetTable 4-14. Address Register Address RegisterTable 4-15. 16- Address Register Definitions Frame Number Registers Table 4-16. Frame Number RegisterTable 4-17. Frame Number Register Definitions Frame NumberToken Register Endpoint for Token Command Table 4-18. Token RegisterTable 4-19. Token Register Definitions Table 4-20. Valid PID TokensEndpoint Control Registers Endpoint EnableTable 4-21. Endpoint Control Registers Table 4-22. Endpoint Control Register DefinitionsHost Mode Operation Table 4-23. Endpoint Control Register DefinitionsSample Host Mode Operations Figure 3. Enable Host Mode and Configure a Target DeviceFigure 4. Full-Speed Bulk Data Transfers to a Target Device USB Pull-up/Pull-down Resistors Figure 4-5. Pull-up/Pull-down USBUSB Interface Signals USB Output EnableHOST Mode Enable Clock CLK5 CAN Controllers CANBUS Background Arbitration and Error CheckingData Exchanges and Communication CANBUS Speed and Length Table 5-1. Bit Rates for Different Cable LengthsCAN Register Summaries Register SummaryHex Offset RegisterHex Offset Detailed CAN Register Map Table 5-4. Detailed CAN Register MapAcceptance Filter Enable Register Hex OffsetRegister CAN Register Definitions TX Message RegistersFigure 5-1. TX Message Routing Sending a MessageTx Message Registers Table 5-5. TxMessage0ID28Table 5-6. TxMessage0ID12 Table 5-7. TxMessage0DataTable 5-12. TxMessage0Ctrl Flags Table 5-13. TxMessage0 Register DefinitionsMessage Identifier for Both Standard and Extended Messages Message DataRX Message Registers Figure 5-2. RX Message RoutingRx Message Registers Table 5-14. RxMessageID28Table 5-15. Rx Message ID28 Register Definitions Table 5-16. RxMessageID12Table 5-20. Rx Message Data Table 5-21. Rx Message Data 39 Register DefinitionsTable 5-22. Rx Message Data Table 5-23. Rx Message Data 23 Register DefinitionsTable 5-26. RxMessage RTR Table 5-27. Rx Message RTR Register DefinitionsTable 5-28. Rx Message Msg Flags Table 5-29. Rx Message Msg Flags Register DefinitionsError Count and Status Registers Table 5-30. Tx/Rx Error CountTable 5-31. Tx\Rx Error Count Register Definitions Table 5-32. Error StatusTable 5-34. Tx/Rx Message Level Register Table 5-35. Tx/Rx Message Level Register Definitionsrxlevel10 txlevel10Interrupt Flags Note The reset value of this register’s bits is indeterminateCRC Error Format ErrorInterrupt Enable Registers Table 5-38. Interrupt Enable RegistersTable 5-39. Interrupt Enable Register Definitions Bus Off State − int2n group error interruptsCAN Operating Mode Table 5-40. Interrupt Enable RegistersTable 5-41. Interrupt Enable Register Definitions Overload Condition − int3n group diagnostic interruptsCAN Configuration Registers Configuration Bit RateFigure 5-3. CAN Operating Mode Table 5-42. Bit Rate Divisor RegisterTable 5-44. Configuration Register Table 5-45. Configuration Register DefinitionsOverwrite Last Message CfgsjwBit Time tseg1 +tseg2 + time quanta TQAcceptance Filter and Acceptance Code Mask Table 5-46. Acceptance Filter Enable RegisterTable 5-47. Acceptance Filter Enable Register Definitions Table 5-48. Acceptance Mask 0 RegisterTable 5-50. Acceptance Mask Register ID Table 5-51. Acceptance Mask Register ID12 DefinitionsTable 5-52. Acceptance Mask Register Data D5556Table 5-54. Acceptance Code Register Table 5-55. Acceptance Code Register DefinitionsTable 5-56. Acceptance Mask Register ID12 Table 5-57. Acceptance Mask Register ID12 DefinitionsCANbus Analysis Arbitration Lost Capture RegisterTable 5-60. Arbitration Lost Capture Register Table 5-61. Arbitration Lost Capture Register DefinitionsError Capture Register Table 5-62. Error Capture RegisterTable 5-63. Error Capture Register Definitions ErrorcodeTable 5-65. Error Capture Register Definitions Frame Reference RegisterTable 5-64. Frame Reference Register Stuff Bit InsertedCAN Bus Interface Interface ConnectionsFigure 5-6. CAN Connector Figure 5-5. CAN Bus InterfaceFigure 5-7. Power for CAN +5CANGNDCAN +24VFigure 5-8. CAN Transceiver and Isolation Circuits 0.01uf
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