Contents
 General Description
Features
 Table of Contents
 PIN Configuration
 A1,A2/ALE
Description of PIN Functions
 Transmission Media Interface
DIP PIN Plcc PIN Name Symbol Description
Miscellaneous
 Instead, it must be connected to XTAL1 with
 COM20020 Operation
 Data Rates
Network Reconfiguration
Protocol Description
Network Protocol
 Broadcast Messages
Extended Timeout Function
Response Time
 Invitations To Transmit
Reconfiguration Time
Idle Time
Line Protocol
 Acknowledgements
Data Packets
Negative Acknowledgements
 System Description
 MULTIPLEXED, 8051-LIKE BUS Interface with RS-485 Interface
 Figure C
 Traditional Hybrid Interface
Backplane Configuration
 COM20020 Network Using RS-485 Differential Transceivers
 Programmable Txen Polarity
Differential Driver Configuration
 Internal Block Diagram
 Cable Type Impedance AT 5MHZ
Functional Description
Attenuation
Nominal
 Read Register Summary
 Write
 Tentative ID Register
Internal Registers
Interrupt Mask Register IMR
Data Register
 Status Register
Diagnostic Status Register
Command Register
Next ID Register
 Configuration Register Setup Register
 BIT BIT Name Symbol Description
 Dupid
BIT BIT Name Symbol Description
 Data Command Description
 Address Pointer Low Register
Address Pointer High Register
 Reset
Configuration Register
 CKP3 CKP2 CKP1
 Sequential Access Operation
 Software Interface
Sequential Access Memory
Access Speed
Internal RAM
 Transmit Sequence
Selecting RAM Page Size
 RAM Buffer Packet Configuration
Page
 Receive Sequence
 Transmit Command Chaining
Command Chaining
 Receive Command Chaining
 Internal Reset Logic
Reset Details
 Initialization Sequence
Improved Diagnostics
 Abnormal Results
Normal Results
 Oscillator
 Operational Description
Maximum Guaranteed Ratings
DC Electrical Characteristics
Parameter Symbol MIN TYP MAX Unit Comment
 XTAL1, XTAL2
 Input Capacitance
 Multiplexed BUS, 68XX-LIKE Control Signals Read Cycle
Timing Diagrams
 Multiplexed 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 Timing
 NTXEN NPULSE1
 TTL Input Timing on XTAL1 PIN
 28-PIN Plcc Package Dimensions
 24-PIN DIP Package Dimensions
 SECTION/FIGURE/ENTRY Correction Revised
Date
 Standard Microsystems Corp