____________________________________ 3 Connection to RS485 bus ____________________________________________________________
__________________________ 4 Modbus protocol _____________________________________________________________________________________________ 9 Appendix: Non-standard RS485 schematics__________________________________________________
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The Modbus socket on the Altivar 31 can be used for the following functions: • • • • Configuration Settings Control Monitoring
The ATV31 drive supports: • The 2-wire RS485 physical layer • TheRTU transmission mode This guide contains information on installation and describes the Modbus services available. The "communication variables" guide describes the operating modes, as well as the Altivar 31 variables and parameters which can be accessed via the communication bus.
Connection to RS485 bus
Connection to ATV31
Connection accessories should be ordered separately (pleaseconsult our catalogues). Connect the RJ45 cable connector to the ATV31 connector.
Protection against interference
• • • • Use the Telemecanique cable with 2 pairs of shielded twisted conductors (reference: TSXCSA100, TSXCSA200, TSXCSA500). Keep the Modbus cable from the power cables (30 cm minimum). Make any crossovers of the Modbus cable and the power cables at right-angles, ifnecessary. Connect the cable shielding to the ground of each device.
For more information, please refer to the TSX DG KBL E guide: "Electromagnetic compatibility of industrial networks and fieldbuses".
RS485 bus schematic
The RS485 standard allows variants of different characteristics: • polarisation • line terminator • distribution of a reference potential • number of slaves • length of busThe new Modbus specification published on the Modbus.org site in 2002 contains precise details of all these characteristics. They are also summarised in the next paragraph (Standard schematic). The new Telemecanique devices conform to this specification. Some devices comply with earlier specifications. The two most widespread are described in the appendices: • "Uni-Telway schematic" page 14 •"Jbus schematic" page 15 Requirements enabling different types of protocol to coexist are given in the appendix: • "Mixed schematic" page 16
Connection to RS485 bus
The standard schematic corresponds to the Modbus specification published on the Modbus.org (Modbus_over_serial_line_V1.pdf, Nov 2002) and in particular to the schematic of the 2-wire multidrop serial bus. TheATV31 drive conforms to this specification. Schematic diagram: site in 2002
5V 650 Ω 650 Ω
D1 120 Ω 1n F D0 Common
Type of trunk cable Shielded cable with 1 twisted pair and at least a 3rd conductor 1000 m at 19200 bps with the Telemecanique TSX CSAppp cable Maximum length of bus Maximum number of stations (without repeater) 32 stations, ie. 31 slaves • 20m for one tap link Maximum length of tap links • 40 m divided by the number of tap links on a multiple junction box • One 450 to 650 Ω pulldown resistor at 5 V (650 Ω recommended) Bus polarisation • One 450 to 650 Ω pulldown resistor at the Common (650 Ω recommended) This polarisation is recommended for the master. One 120 Ω 0.25 W resistor in series with a 1nF 10 V capacitor Line terminator...