Directed Electronics MERLIN 2000 Specifications

No-one in the world does more with electricity Technical Guide 2000 MODBUS Network Guide Merlin Gerin

9 Schneider Electric Review Definitions and limitations Warning Choosing components Only components complying with EMC standards should be used. Cabl

10 Schneider Electric Review (continued) Protective earthing vs. grounding (equipotential bonding) Earth The interconnection of the various exposed

11 Schneider Electric Review (continued) Protective earthing Protection of personsProtection against electrostatic dischargesProtection against ligh

12 Schneider Electric Review (continued) Grounding The interconnection of all metal parts (building structures, pipes, cableways, equipment, equipme

13 Schneider Electric Review (continued) To be effective, an underground network must be in the form of a grid:b For small premises (less than about

14 Schneider Electric Review (continued) Example of a grounding system for a building An effective solution is the interconnection of the metal stru

15 Schneider Electric Review (continued) Protection against penetration Common mode currents coming from the outside must be evacuated by the earthi

16Schneider ElectricReview (continued)Example of a grounding system for an islandWhen electronic equipment is grouped together in an area no larger th

17Schneider ElectricReview (continued)Power system earthing arrangementsTT systemNote that overvoltages may be caused by separate earth electrodes for

18Schneider ElectricReview (continued)TN-S systemIT systemAn initial insulation fault can lead to a phase-to-phase voltage between a phase conductor a

1 Schneider Electric Introduction Overview 3Local Area Networks 4Warning 5

19Schneider ElectricReview (continued)EMC phenomenaDisturbances and their effectsb Whether conducted or radiated, their presence generates common-mode

20Schneider ElectricChoice of the Physical Communication MediumVarious Types of Physical Media Two types of shielding: Note: Shielded cable with a sim

21Schneider ElectricChoice of the Physical Communication Medium (continued)Equivalent diagram:E = TransmitterL = Series inductanceR = Series resistanc

22Schneider ElectricChoice of the Physical Communication Medium (continued)Attenuation in dB/km:b This is the loss of signal quality in terms of ampli

23Schneider ElectricChoice of the Physical Communication Medium (continued)Example of a choice of mediumb Characteristic impedance: 120 Ω.b Attenuatio

24Schneider ElectricImplementation guidelinesSensitivity of various types of cableNote: Shielded cables are not sensitive and do not generate interfer

25Schneider ElectricImplementation guidelines (continued)How should the shielding be connected?A secure connection of the shielding to a cable gland i

26Schneider ElectricImplementation guidelines (continued)Using filtersThree rules must be followed when installing a filter:b Reference the filter shee

27Schneider ElectricImplementation guidelines (continued)Principal cabling rulesb Work with pairs for digital or analogue signals.Inside cabinets, be

28Schneider ElectricImplementation guidelines (continued)b Separate analogue and digital signals with a row of 0 V pins if they use the same connector

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29Schneider ElectricImplementation guidelines (continued)Protection inside a cabinet or small machineb Clamp all cables against equipotential structur

30Schneider ElectricImplementation guidelines (continued)Cabling between two cabinetsProtection of cabling outside equipmentThe potential reference pl

31Schneider ElectricImplementation guidelines (continued)Placing cabinets togetherWhen equipment is placed in a number of side-by-side cabinets the fo

32Schneider ElectricImplementation guidelines (continued)b Attach unshielded cables in corners of chutes.b Use a vertical separation in the trunking t

33Schneider ElectricImplementation guidelines (continued)Whenever one of the three conditions is not completely met, the physical length of the trunki

34Schneider ElectricImplementation guidelines (continued)Error rate for a slow link:Transmission of 41222 bytes at 4800 Bds. IEC test 1000-4-4. 15-pa

35Schneider ElectricSummaryEssential rulesb Make sure all exposed conductive parts have the same potential..b Choose equipment that complies with stan

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37Schneider ElectricGuide to IntegrationReview 40Networks 40Systems 40Bauds and bits per second 40Architectures 41The 20 mA current loop 42The RS232 l

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3 Schneider Electric Overview Networks can be classified according to the area they cover:b WAN: Wide Area Network. b MAN: Metropolitan Area Network.

39Schneider ElectricThis chapter describes layer 2 of the OSI model in detail. This layer is composed of two separate parts for data transmission:b A

40Schneider ElectricReview Networks A network is defined by its:b Topology (bus, ring, star, tree, mesh, etc.)b Physical limits (length, speed, number

41Schneider Electric20 mA CL – RS232 – RS422 – RS485 linksArchitectures(Connection on SubD9 recommended, maximum length 3000 m at 1200 Bds, and 300 m

42Schneider Electric20 mA CL – RS232 – RS422 – RS485 links (continued)The 20 mA current loopA 20 mA current obtained from the power supply voltage (12

43Schneider Electric20 mA CL – RS232 – RS422 – RS485 links (continued)The RS232 linkThe physical DB25-DB25 connection Definition: DTE (Data Terminal E

44Schneider Electric20 mA CL – RS232 – RS422 – RS485 links (continued)The DB9-DB25 physical connectionSome terminals and computers may have a DB9 type

45Schneider Electric20 mA CL – RS232 – RS422 – RS485 links (continued)Standard cablingNul-modem cableNul-terminal cableE52329E52330E52331123456782022D

46Schneider Electric20 mA CL – RS232 – RS422 – RS485 links (continued)RTS/CTS or XON/XOFF flow controlThe hardware method is recommended: it uses sign

47Schneider Electric20 mA CL – RS232 – RS422 – RS485 links (continued)RS485 link Type of connector:b A "SubD 9 points" connector is recommen

48Schneider Electric20 mA CL – RS232 – RS422 – RS485 links (continued)Standards EIA 485A (March 98 update) and TSB89 (application guidelines for TIA/E

4 Schneider Electric Local Area Networks Local Area Networks have been standardized according to the OSI model. Definition: OSI, Open Systems Inter

49Schneider Electric20 mA CL – RS232 – RS422 – RS485 links (continued)Signal transition time:Vss = | Vt - Vt* |Constraints concerning signal form:b tr

50Schneider ElectricInterfacesRS232/RS485 Definition of an RS232/RS485 interface:b RS232:v conformity with the EIA standard,v PC connection cable <

51Schneider ElectricInterfaces (continued)ModemsBits cannot be transmitted directly over a telephone line (except for an ISDN line). A telephone conv

52Schneider ElectricInterfaces (continued)Telephone companies dispatch pairs of cables to their clients; each pair represents a different telephone nu

53Schneider ElectricInterfaces (continued)Definition: The modulation speed of the modem must not be confused with the speed of the COM port on the com

54Schneider ElectricInterfaces (continued)Modem parameters:b Error correction can be used to eliminate a number of transmission errors on the often di

55Schneider ElectricInterfaces (continued)The right cable The serial link cable between the modem and the PC/Mac/terminal (DTE) should include all the

56Schneider ElectricThe Modbus ProtocolDifference between ASCII and RTU frames Some devices can use either of the two formats:b With the RTU format th

57Schneider ElectricThe Modbus Protocol (continued)Note: Function 13 has 43 sub-functions; Jbus uses only 6..The Modbus protocol can be used to read o

58Schneider ElectricThe Modbus Protocol (continued)Description of exchanges Broadcast commands are always write commands. Slaves do not answer such co

5 Schneider Electric Warning If the recommendations in this manual are incompatible with instructions for a given device, the device instructions sho

59Schneider ElectricThe Modbus Protocol (continued)Each frame includes four types of information:b Slave number (1 byte):v the slave number specifies t

60Schneider ElectricThe Modbus Protocol (continued)Principles usedSynchronisation of exchanges Any character received after a silence of more than 3 c

61Schneider ElectricThe Modbus Protocol (continued)Addressing The addressing mode differs according to the module:b With a code wheel:v wheel no. 1 gi

62Schneider ElectricThe Modbus Protocol (continued)Control of messages received by the slave Contents of an exception response Example:b Query.b Respo

63Schneider ElectricThe Modbus Protocol (continued)Definition: A bit is a basic unit of information that can only equal 1 or 0. Bits are the "l

64Schneider ElectricThe Modbus Protocol (continued) Note: In this case the "word" represents 2 bytes or 16 bits..Read n words: function 3 or

65Schneider ElectricThe Modbus Protocol (continued)Write a bit: function 5 b Query. bit forced to 0_ write 0bit forced to 1_ write FFb Response.Note:

66Schneider ElectricThe Modbus Protocol (continued)Fast read 8 bits: function 7 b Query.b Response.The addresses of the 8 bits are set by the slave. E

67Schneider ElectricThe Modbus Protocol (continued)Read diagnostic counters: function 8 b Query/response. (1) For the query XXXX equals 00 00.For the

68Schneider ElectricThe Modbus Protocol (continued)Read event counters: function 11 Each slave has an event counter. The master also has an event cou

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69Schneider ElectricThe Modbus Protocol (continued)Read trace buffer: function 12 Note: Functions 12, 13 and 14 are not implemented in all Modicon con

70Schneider ElectricThe Modbus Protocol (continued)Program commands: Function 13 Program commands can be used to perform the following functions:b Con

71Schneider ElectricThe Modbus Protocol (continued)Diagnostic of program commands: Function 14 This command is used to indicate the diagnostic associa

72Schneider ElectricThe Modbus Protocol (continued) Write n consecutive bits: function 15 b Query. b Response. Example:Force bits 200 and 201 of slave

73Schneider ElectricThe Modbus Protocol (continued)Write n consecutive words: function 16 b Query.b Response.Example:Force words 0800 to 0803 of slave

74Schneider ElectricThe Modbus Protocol (continued)Identification of a slave: function 17 (specific to PM 6xx/CM2xxx). b Query.b Response. Note: The n

75Schneider ElectricThe Modbus Protocol (continued)Algorithm for generating CRC16+ exclusive ORn = number of data bitsPOLY = polynomial for generating

76Schneider ElectricThe Modbus Protocol (continued)Example of CRC calculation: frame 020B = read event counter (function 11) of the slave at 02h.Thus

77Schneider ElectricThe Modbus Protocol (continued)Electrical interpretation of the CRC on a RS485 network:v In our example, the query from the master

78Schneider ElectricThe Modbus Protocol (continued)"Physical" example of a frame:b "Master" frames are transmitted by a specific so

7 Schneider Electric Cabling Guidelines Review 9 Definitions and limitations 9Protective earthing vs. grounding (equipotential bonding) 10Power syste

79Schneider ElectricSchneider SpecificationsOverview .Choice of a physical interface (RS232C, RS422A, RS485, 20 mA CL) depends on the environment and

80Schneider ElectricSchneider Specifications (continued) b The time between two characters in a frame must always be less than three characters (1 cha

81Schneider ElectricSchneider Specifications (continued) Counter management algorithmE52405Unknown function codeSlave number =Slave number of the stat

82Schneider ElectricSchneider Specifications (continued) Counter management algorithm (continued)E524043Unknown function codeFunction code not authori

83Schneider ElectricSchneider Specifications (continued)Connection 4-wire slave without polarisation or adaptationSlave without polarisation or adapta

84Schneider ElectricSchneider Specifications (continued)Components availableSee reference document:b In French: PCRED 399074FR, art 28992.b In English

85Schneider ElectricSummary RS232C:b Limit length to 15 m.b Take into account the specific requirements of each interface and software program with reg

86Schneider ElectricSpecific Characteristics of Products Product Functions supportedTime stampingFrame format / speedConnection Electrical interfaceDC

87Schneider ElectricImplementation in ProductsDiagnostic tools 89List of diagnostic tests 89

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89Schneider ElectricDiagnostic toolsList of diagnostic testsControl:b Are the frames received/sent compatible with the functions supported by the cont

90Schneider Electricb UTE – C 15-900: "Mise en œuvre et cohabitation des réseaux de puissance et des réseaux de communication dans les installat

91Schneider ElectricIndexNumerics20mA current loop 41AA/D 52Address 61ASCII 56Attenuation 22BBaud 40Bits per second 40Broadcast 59CCaller 52C

92Schneider ElectricIndex (continued)MMaster 58Maximum theoretical length for electromagnetic compatibility 32Modbus protocol 56Modbus+ protocol 5

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