SMSC COM20020 manual Next ID Register, Diagnostic Status Register, Command Register

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Transmitter is disabled, the Receiver portion of the device is still functional and will provide the user with useful information about the network. The Node ID Register defaults to the value 0000 0000 upon hardware reset only.

Next ID Register

The Next ID Register is an 8-bit, read-only register, accessed when the sub-address bits are set up accordingly (please refer to the Configuration Register). The Next ID Register holds the value of the Node ID to which the COM20020 will pass the token. When used in conjunction with the Tentative ID Register, the Next ID Register can provide a complete network map. The Next ID Register is updated each time a node enters/leaves the network or when a network reconfiguration occurs. Each time the microsequencer updates the Next ID Register, a New Next ID interrupt is generated. This bit is cleared by reading the Next ID Register. Default value is 0000 0000 upon hardware or software reset.

Status Register

The COM20020 Status Register is an 8-bit read- only register. All of the bits, except for bits 5 and 6, are software compatible with previous SMSC ARCNET devices. In previous SMSC ARCNET devices the Extended Timeout status was provided in bits 5 and 6 of the Status Register. In the COM20020, the COM90C66,

and the COM90C165, COM20020-5, COM20051 and COM20051+ these bits exist in and are controlled by the Configuration Register. The Status Register contents are defined as in Table 4, but are defined differently during the Command Chaining operation. Please refer to the Command Chaining section for the definition of the Status Register during Command

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Chaining operation. The Status Register defaults to the value 1XX1 0001 upon either hardware or software reset.

Diagnostic Status Register

The Diagnostic Status Register contains seven read-only bits which help the user troubleshoot the network or node operation. Various combinations of these bits and the TXEN bit of the Configuration Register represent different situations. All of these bits, except the Excessive NAcK bit and the New Next ID bit, are reset to logic "0" upon reading the Diagnostic Status Register or upon software or hardware reset. The EXCNAK bit is reset by the "POR Clear Flags" command or upon software or hardware reset. The Diagnostic Status Register defaults to the value 0000 000X upon either hardware or software reset.

Command Register

Execution of commands are initiated by performing microcontroller writes to this register. Any combinations of written data other than those listed in Table 6 are not permitted and may result in incorrect chip and/or network operation.

Address Pointer Registers

These read/write registers are each 8-bits wide and are used for addressing the internal RAM. New pointer addresses should be written by first writing to the High Register and then writing to the Low Register because writing to the Low Register loads the address. The contents of the Address Pointer High and Low Registers are undefined upon hardware reset. Writing to Address Pointer low loads the address.

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Contents General Description FeaturesTable of Contents PIN Configuration A1,A2/ALE Description of PIN FunctionsMiscellaneous DIP PIN Plcc PIN Name Symbol DescriptionTransmission Media Interface Instead, it must be connected to XTAL1 with COM20020 Operation Data Rates Network ReconfigurationProtocol Description Network ProtocolResponse Time Extended Timeout FunctionBroadcast Messages Invitations To Transmit Reconfiguration TimeIdle Time Line ProtocolNegative Acknowledgements Data PacketsAcknowledgements System Description MULTIPLEXED, 8051-LIKE BUS Interface with RS-485 Interface Figure C Traditional Hybrid Interface Backplane ConfigurationCOM20020 Network Using RS-485 Differential Transceivers Programmable Txen Polarity Differential Driver ConfigurationInternal Block Diagram Cable Type Impedance AT 5MHZ Functional DescriptionAttenuation NominalRead Register Summary Write Tentative ID Register Internal RegistersInterrupt Mask Register IMR Data RegisterStatus Register Diagnostic Status RegisterCommand Register Next ID RegisterConfiguration Register Setup Register BIT BIT Name Symbol Description Dupid BIT BIT Name Symbol DescriptionData Command Description Address Pointer Low Register Address Pointer High RegisterReset Configuration RegisterCKP3 CKP2 CKP1 Sequential Access Operation Software Interface Sequential Access MemoryAccess Speed Internal RAMTransmit Sequence Selecting RAM Page SizeRAM Buffer Packet Configuration Page Receive Sequence Transmit Command Chaining Command ChainingReceive Command Chaining Internal Reset Logic Reset DetailsInitialization Sequence Improved DiagnosticsAbnormal Results Normal ResultsOscillator Operational Description Maximum Guaranteed RatingsDC Electrical Characteristics Parameter Symbol MIN TYP MAX Unit CommentXTAL1, XTAL2 Input Capacitance Multiplexed BUS, 68XX-LIKE Control Signals Read Cycle Timing DiagramsMultiplexed BUS, 80XX-LIKE Control Signals Read Cycle Multiplexed BUS, 68XX-LIKE Control Signals Write Cycle Multiplexed BUS, 80XX-LIKE Control Signals Write Cycle NON-MULTIPLEXED BUS, 80XX-LIKE Control Signals Read Cycle NON-MULTIPLEXED BUS, 68XX-LIKE Control Signals Read Cycle NON-MULTIPLEXED BUS, 80XX-LIKE Control Signals Write Cycle NON-MULTIPLEXED BUS, 68XX-LIKE Control Signals Write Cycle These signals are to and from the hybrid Normal Mode Transmit or Receive TimingNTXEN NPULSE1 TTL Input Timing on XTAL1 PIN 28-PIN Plcc Package Dimensions 24-PIN DIP Package Dimensions SECTION/FIGURE/ENTRY Correction Revised DateStandard Microsystems Corp
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