Appendix, RS485 standard | Schneider Electric VW3 A3 303 guide

9. Appendix

9. 1. RS485 standard

The RS485 standard (ANSI/TIA/EIA-485-A-1998) allows variants of certain characteristics:

•Polarization

•Line termination

•Distribution of a reference potential

•Number of slaves

•Length of bus

It does not specify the connector type or pinout.

The Modbus specification published on www.modbus.org in 2002 contains precise details of all these characteristics. They are also summarized in the next sections (Modbus 2-wire and 4-wire standard schematics). The latest generation Telemecanique devices (Altivar 31, Altivar 71, etc.) conform to this specification.

Older devices comply with earlier specifications. The two most widespread are described in the following sections:

•"Uni-Telway schematic" page 42

•"Jbus schematic" page 43

Requirements enabling different types of protocol to coexist are given in the following section in this appendix:

• "Creating a Modbus bus using non-standard equipment" on page 45

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Schneider Electric VW3 A3 303 user manual Appendix, RS485 standard

Contents

Altivar Contents Electric shock will result in death or serious injury Before you begin Communication Parameters Manual Installation ManualDocumentation structure Programming Manual Introduction PresentationNotation Hardware description Hardware setupInstalling the card in the drive Receipt Switch coding Choosing polarizationCoding the address 1234 Address Connecting to the bus Wiring recommendationsModbus RS485 standard Connection via RJ45 wiring system Connection accessoriesConnection cables TSX SCP CM Connection cables for the masterType of master Master interface Description Catalog number TWD XCA RJ030 Cables Connection via junction boxesDescription Catalog Number Subscriber socket RS485 double shielded twisted pair TSX P ACC TSX CSA500 Communication parameters Configuration Parameter Value Comment Control CommandControl via Modbus in I/O profile Control via Modbus or the terminals in I/O profile Control via Modbus or the terminals in Drivecom profile Control via Modbus in Drivecom profile Configuration COM. Scanner Input Example of configuration via the graphic display terminalCommunication scanner RDY NET COM. Fault Management Communication faults Format Range Terminal display CONFIG. COMM. MAPMonitored parameters Format Green RUN Red ERR Meaning Corrective action DiagnosticsChecking the address LEDs COM Scan Output MAP CMD. Word Image RUN NETCommunication MAP COM. Scanner Input MAP Input variable Scanner parameter Output variable Scanner parameterCOM Scan Output MAP Card fault Communication fault Modbus protocol PrincipleSlave Slave j Slave k Slave address Function code Data RTU modeAscii mode Modes Modbus functions available Read Holding/Input Registers 3/4Code Modbus name Description Broadcast Size of data Write Single Register Diagnostics Write Multiple Registers 16 = 16#10 Get Comm Event Counter 11 = 16#0B Read/Write Multiple Registers 23 = 16#17 Machine Read Device Identification 43 = 16#2B MEI Example of positive response Output variables Logic address Default assignment Input variables Logic address Default assignmentCode Modbus name Description Size of data Input variable address Logic address Default value Parameter Logic ReadParameter Logic Value Parameter assigned Output controlParameter assigned Input monitoring Code Error code Exception responsesResponse Logic address Parameter Value Read non-existent or protected parameters RS485 standard Appendix Master Modbus 2-wire standard schematic Modbus 4-wire standard schematic Uni-Telway schematic Type of trunk cable Cable with 1 shielded twisted pair Wire Jbus schematic Creating a Modbus bus using non-standard equipment Different scenariosRecommendations Example Calculating the polarization SUB-D RS485 schematic for the cardCard connector pinout Contact no. Signal Atv71ModbusJbusENV1 2005-05