Lantronix DSTni-EX manual Bus Clock Considerations, Bus Clock Speed, Clock Synchronization

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Bus Clock Considerations

Bus Clock Speed

The I2C bus can be defined for bus clock speeds up to 100 Kb/s and up to 400 Kb/s in fast mode.

To detect START and STOP conditions on the bus, the M I2C must sample the I2C bus at least 10 times faster than the fastest master bus clock on the bus. The sampling frequency must be at least 1 MHz (4 MHz in fast-mode) to guarantee correct operation with other bus masters.

The CLK input clock frequency and the value in CCR bits 2 - 0 determine the I2C sampling frequency. When the I2C controller is in the master mode, it determines the frequency of the CLK input and the values in bits [2:0] and [6:3] of the Clock Control register (see Clock Control Register on page 28).

Clock Synchronization

If another device on the I2C bus drives the clock line when the I2C controller is in master mode, the I2C controller synchronizes its clock to the I2C bus clock.

The device that generates the shortest high clock period determines the high period of the clock.

The device that generates the longest LOW clock period determines the LOW period of the clock.

When the I2C controller is in master mode and is communicating with a slow slave, the slave can stretch each bit period by holding the SCL line LOW until it is ready for the next bit. When the I2C controller is in slave mode, it holds the SCL line LOW after each byte transfers until the IFLG clears in the Control register.

Bus Arbitration

In master mode, the I2C controller checks that each logical 1 transmitted appears on the I2C bus as a logical 1. If another device on the bus overrules and pulls the SDA line LOW, arbitration is lost.

If arbitration is lost:

While a data byte or Not-Acknowledge bit is being transmitted, the I2C controller returns to the idle state.

During the transmission of an address, the I2C controller switches to slave mode so that it can recognize its own slave address or the general call address.

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Contents Section Five DSTni-EX User GuidePage Lantronix Copyright & TrademarkTechnical Support Master DistributorWarranty 1 About This User Guide Contents2 SPI Controller 3 I2C Controller5 CAN Controllers List of TablesTable 3-17. Clock Control Register List of Figures 1 About This User Guide Conventions Intended AudienceNavigating Online Notes Notes are information requiring attentionOrganization Theory of Operation 2 SPI ControllerSPI Background DSTni SPI ControllerTable 2-1. SPI Controller Register Summary SPI Controller Register SummarySPIDATA Register SPI Controller Register DefinitionsRESET Table 2-2. SPIDATA RegisterInterrupt Request Enable CTL RegisterPhase Select Wire-OTable 2-6. SPISTAT Register SPISTAT RegisterTable 2-7. SPISTAT Register Definitions Interrupt RequestTable 2-10. BCNT Bit Settings SPISSEL RegisterSelectO Signal Table 2-8. SPISSEL RegisterDVDCNTRHI DVDCNTRLO RegisterTable 2-11. DVDCNTRLO Register Table 2-12. DVDCNTRLO Register Definitions3 I2C Controller FeaturesFigure 3-1. DSTni I2C Controller Block Diagram Block DiagramI2C Background Master Transmit Mode I2C ControllerOperating Modes Code Table 3-1. Master Transmit Status CodesI2C State Microprocessor ResponseTable 3-2. Codes After Servicing Interrupts Master Transmit Servicing the InterruptTable 3-3. Status Codes After Each Data Byte Transmits Transmitting Each Data ByteAll Bytes Transmit Completely Master Receive ModeTable 3-4. Master Receive Status Codes Table 3-5. Codes After Servicing Interrupt Master Receive Slave Transmit Mode Receiving Each Data ByteTable 3-6. Codes After Receiving Each Data Byte Slave Receive Mode Bus Clock Speed Bus Clock ConsiderationsClock Synchronization Bus ArbitrationI2C Controller Register Summary Programmer’s ReferenceResetting the I2C Controller Table 3-7. I 2C Controller Register SummarySlave Address Register I2C Controller Register DefinitionsGeneral Call Address Enable Table 3-8. Slave Address RegisterTable 3-10. Data Register Data RegisterTable 3-12. Control Register Control RegisterTable 3-13. Control Register Definitions Extended Slave AddressTable 3-14. Status Register Status RegisterStatus Code Table 3-15. Status Register DefinitionsTable 3-16. Status Codes Table 3-18. Clock Control Register Definitions Clock Control RegisterTable 3-17. Clock Control Register Extended Slave Address Register Software Reset RegisterTable 3-21. Software Reset Register Table 3-22. Software Reset Register Definitions4 USB Controller USB Interrupt USB BackgroundUSB Core Serial Interface EngineDigital Phase Lock Loop Logic USB Hardware/Software InterfaceMicroprocessor Interface Buffer Descriptor TableRx vs. Tx as a Target Device or Host Figure 4-1. Buffer Descriptor TableAddressing BDT Entries Table 4-1. USB Data DirectionTable 4-2. 16-Bit USB Address Table 4-3. 16-Bit USB Address DefinitionsUSB Controller Determines… Table 4-4. BDT Data Used by USB Controller and MicroprocessorMicroprocessor Determines… Table 4-5. USB Buffer Descriptor FormatBD Owner Table 4-6. USB Buffer Descriptor Format DefinitionsDATA0/1 Transmit or Receive USB OwnershipFigure 4-2. USB Token Transaction USB TransactionDedicated to host mode USB Register SummaryTable 4-7. USB Register Summary Interrupt Status Register USB Register DefinitionsTable 4-8. Interrupt Status Register Table 4-9. 16- Interrupt Status Register DefinitionsSleep Timer Enable/Disable USBRST InterruptError Condition USB ResetTable 4-11. 16- Error Interrupt Status Register Definitions Error RegisterTable 4-10. Error Interrupt Status Register Data Field Received Not 8 Bits Error interrupt with two functionsCRC16 Failure PID check field failedLive USB Single Ended Zero Signal Live USB Differential Receiver JSTATE SignalTable 4-12. Status Register Table 4-13. Status Register DefinitionsHost Mode Enable valid for host mode only USB Reset SignalResume Signaling BDT PDD ResetTable 4-15. 16- Address Register Definitions Address RegisterTable 4-14. Address Register Table 4-16. Frame Number Register Frame Number RegistersTable 4-17. Frame Number Register Definitions Frame NumberToken Register Table 4-18. Token Register Endpoint for Token CommandTable 4-19. Token Register Definitions Table 4-20. Valid PID TokensEndpoint Enable Endpoint Control RegistersTable 4-21. Endpoint Control Registers Table 4-22. Endpoint Control Register DefinitionsTable 4-23. Endpoint Control Register Definitions Host Mode OperationFigure 3. Enable Host Mode and Configure a Target Device Sample Host Mode OperationsFigure 4. Full-Speed Bulk Data Transfers to a Target Device Figure 4-5. Pull-up/Pull-down USB USB Pull-up/Pull-down ResistorsUSB Output Enable USB Interface SignalsHOST Mode Enable Clock CLK5 CAN Controllers Data Exchanges and Communication Arbitration and Error CheckingCANBUS Background Table 5-1. Bit Rates for Different Cable Lengths CANBUS Speed and LengthRegister Summary CAN Register SummariesHex Offset RegisterRegister Table 5-4. Detailed CAN Register Map Detailed CAN Register MapHex Offset Acceptance Filter Enable RegisterRegister TX Message Registers CAN Register DefinitionsFigure 5-1. TX Message Routing Sending a MessageTable 5-5. TxMessage0ID28 Tx Message RegistersTable 5-6. TxMessage0ID12 Table 5-7. TxMessage0DataTable 5-13. TxMessage0 Register Definitions Table 5-12. TxMessage0Ctrl FlagsMessage Identifier for Both Standard and Extended Messages Message DataFigure 5-2. RX Message Routing RX Message RegistersTable 5-14. RxMessageID28 Rx Message RegistersTable 5-15. Rx Message ID28 Register Definitions Table 5-16. RxMessageID12Table 5-21. Rx Message Data 39 Register Definitions Table 5-20. Rx Message DataTable 5-22. Rx Message Data Table 5-23. Rx Message Data 23 Register DefinitionsTable 5-27. Rx Message RTR Register Definitions Table 5-26. RxMessage RTRTable 5-28. Rx Message Msg Flags Table 5-29. Rx Message Msg Flags Register DefinitionsTable 5-30. Tx/Rx Error Count Error Count and Status RegistersTable 5-31. Tx\Rx Error Count Register Definitions Table 5-32. Error StatusTable 5-35. Tx/Rx Message Level Register Definitions Table 5-34. Tx/Rx Message Level Registerrxlevel10 txlevel10Note The reset value of this register’s bits is indeterminate Interrupt FlagsCRC Error Format ErrorTable 5-38. Interrupt Enable Registers Interrupt Enable RegistersTable 5-39. Interrupt Enable Register Definitions Bus Off State − int2n group error interruptsTable 5-40. Interrupt Enable Registers CAN Operating ModeTable 5-41. Interrupt Enable Register Definitions Overload Condition − int3n group diagnostic interruptsConfiguration Bit Rate CAN Configuration RegistersFigure 5-3. CAN Operating Mode Table 5-42. Bit Rate Divisor RegisterTable 5-45. Configuration Register Definitions Table 5-44. Configuration RegisterOverwrite Last Message Cfgsjwtseg1 + Bit Timetseg2 + time quanta TQTable 5-46. Acceptance Filter Enable Register Acceptance Filter and Acceptance Code MaskTable 5-47. Acceptance Filter Enable Register Definitions Table 5-48. Acceptance Mask 0 RegisterTable 5-51. Acceptance Mask Register ID12 Definitions Table 5-50. Acceptance Mask Register IDTable 5-52. Acceptance Mask Register Data D5556Table 5-55. Acceptance Code Register Definitions Table 5-54. Acceptance Code RegisterTable 5-56. Acceptance Mask Register ID12 Table 5-57. Acceptance Mask Register ID12 DefinitionsArbitration Lost Capture Register CANbus AnalysisTable 5-60. Arbitration Lost Capture Register Table 5-61. Arbitration Lost Capture Register DefinitionsTable 5-62. Error Capture Register Error Capture RegisterTable 5-63. Error Capture Register Definitions ErrorcodeFrame Reference Register Table 5-65. Error Capture Register DefinitionsTable 5-64. Frame Reference Register Stuff Bit InsertedInterface Connections CAN Bus InterfaceFigure 5-6. CAN Connector Figure 5-5. CAN Bus Interface+5CAN Figure 5-7. Power for CANGNDCAN +24V0.01uf Figure 5-8. CAN Transceiver and Isolation Circuits