Schneider Electric VW3 A3 303 Creating a Modbus bus using non-standard equipment, Recommendations

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9. Appendix

9. 6. Creating a Modbus bus using non-standard equipment

bDifferent scenarios

MIf the Modbus bus is created using the latest-generation Telemecanique devices and Telemecanique Modbus wiring accessories, installation is simple and no calculation is required (see the section entitled "Connecting to the bus").

MIf a new Modbus bus has to be created using devices of different brands or older-generation devices, which do not comply with the Modbus standard, several checks are required (see "Recommendations" below).

MIf, on an existing Modbus bus, a device with 4.7 kΩ polarization is to be replaced by a new-generation device, set the 2 polarization switches to the lower position to activate the card’s 4.7 kΩ polarization.

Polarization switches:

4.7 kΩ RS485 line polarization at drive level

bRecommendations

1.Identify the polarities D0 and D1.

They are labeled in different ways depending on the standard:

			Standard

	Modbus	EIA/TIA-485		Uni-Telway	Jbus
		(RS 485)

	D0	A/A’		D (A)	RD +/TD + or L +
Signals
Signals	D1	B/B’		D (B)	RD -/TD - or L -

	Common	C/C’		0VL

Generator	B	G

Receiver	R	R

However, certain RS485 electronic components are labeled in the opposite way to the EIA/TIA-485 standard.

It may be necessary to perform a test by connecting a master to a slave, then reversing the connection in the event of failure.

2.Check polarizations

Check the documentation supplied with the devices to determine their polarization.

If there is a polarization, check that the equivalent polarization value is correct (see "Calculating the polarization").

It is not always possible to implement correct polarization (for example, if the 5 V is not available on the master). In this case, it may be necessary to limit the number of slaves.

3.Choose a line terminator

If there is a polarization, select an RC line terminator (R = 120 Ω, C = 1 nF)

If it is not possible to install a polarization, select an R line terminator (R = 150 Ω).

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Contents Altivar Contents Before you begin Electric shock will result in death or serious injuryInstallation Manual Documentation structureProgramming Manual Communication Parameters ManualNotation IntroductionPresentation Hardware setup Installing the card in the driveReceipt Hardware descriptionCoding the address Switch codingChoosing polarization Address 1234Modbus RS485 standard Connecting to the busWiring recommendations Connection cables Connection via RJ45 wiring systemConnection accessories Connection cables for the master Type of master Master interface Description Catalog numberTWD XCA RJ030 TSX SCP CMConnection via junction boxes Description Catalog Number Subscriber socketRS485 double shielded twisted pair CablesTSX CSA500 TSX P ACCConfiguration Communication parametersControl Command Control via Modbus in I/O profileControl via Modbus or the terminals in I/O profile Parameter Value CommentControl via Modbus in Drivecom profile Control via Modbus or the terminals in Drivecom profileConfiguration Example of configuration via the graphic display terminal Communication scannerRDY NET COM. Scanner InputCommunication faults COM. Fault ManagementCONFIG. COMM. MAP Monitored parametersFormat Format Range Terminal displayDiagnostics Checking the addressLEDs Green RUN Red ERR Meaning Corrective actionRUN NET Communication MAPCOM. Scanner Input MAP COM Scan Output MAP CMD. Word ImageCOM Scan Output MAP Input variable Scanner parameterOutput variable Scanner parameter Communication fault Card faultSlave Slave j Slave k Modbus protocolPrinciple RTU mode Ascii modeModes Slave address Function code DataCode Modbus name Description Broadcast Size of data Modbus functions availableRead Holding/Input Registers 3/4 Write Single Register Diagnostics Get Comm Event Counter 11 = 16#0B Write Multiple Registers 16 = 16#10Read/Write Multiple Registers 23 = 16#17 Read Device Identification 43 = 16#2B MachineExample of positive response MEICode Modbus name Description Size of data Output variables Logic address Default assignmentInput variables Logic address Default assignment Parameter Logic Input variable address Logic address Default valueParameter Logic Read Output control Parameter assignedInput monitoring Value Parameter assignedResponse Code Error codeException responses Read non-existent or protected parameters Logic address Parameter ValueAppendix RS485 standardModbus 2-wire standard schematic Master Modbus 4-wire standard schematic Uni-Telway schematic Wire Jbus schematic Type of trunk cable Cable with 1 shielded twisted pairRecommendations Creating a Modbus bus using non-standard equipmentDifferent scenarios Calculating the polarization ExampleRS485 schematic for the card Card connector pinoutContact no. Signal SUB-DAtv71ModbusJbusENV1 2005-05