Monarch Instrument DataChart 2000 Modbus Protocol

Chapter 7 Communications Interface

This chapter primarily describes the communications interface protocol for the Recorder.

7.1 Description

The Communications Interface is a field installable option. The user can choose either an RS232 compatible communications port, or an RS485 compatible communications port. An RS232C interface allows a single Data Recorder to communicate with a computer at a distance of up to 50 feet (16m). An RS485 interface is required for distances up to 4000 feet (1300m).

An RS485 interface will support up to 31 Data Recorders linked to a single computer. Each of the Recorders will be identified by a unique unit address (programmed under “Com Ports” in the Programming Menu).

Two modes of operation, Modbus RTU and Modbus ASCII, are supported in RS232C and RS485 communication interfaces.

7.1.1 Port Set Up

Refer to Chapter 5-10 Programming - Com Ports, for communications setup programming information.

7.1.2 Port Communications Wiring

Refer to Chapter 2-4, Installation and Wiring - Serial Ports, for wiring instructions of the communications port.

7.1.3 Modbus RTU and ASCII Functions

This Recorder supports a subset of the Modbus protocol ASCII and RTU. The functions included in the subset are:

Function 1 - Read Coil Status Function 2 - Read Input Status Function 3 - Read Holding Registers Function 4 - Read Input Registers Function 5 - Force Single Coil Function 6 - Preset Single Register Function 15 - Force Multiple Coils Function 16 - Preset Multiple Registers

NOTE: Many registers are reserved or are not used. Use the defined registers only.

7.1.4 Modbus Registers

Tables 7-1 through 7-8 show the mapping of the recorder parameters into Modbus registers. Knowledge of these Modbus register assignments is only needed to make use of third party communications software.

NOTE: The Registers flagged as “Reserved” are intended for the Companion software only and should not be used with any other software.

7.1.5 Modbus Floating Point Formats

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Chapter 7 Communications Interface

The registers most users will be interested in are the Point 1-C Data Registers. These registers hold the current floating point value for each data point. The actual Modbus specification has no mention of floating point numbers. Therefore several common methods of transferring a floating point number has emerged. We support two of those methods. One method is compatible with the Modicon 984 PSC and the other is sometimes referred to as the Daniel’s Extension.

IEEE floating point number requires 4 bytes (2 words). The modbus registers are all 2 bytes (1 word).

Sign Bit Exponent Mantissa (+127 biased) (extra implied 1 bit) 1 bit 8 bits 23 bits

Modicon 984 PLC Compatible Format (2 register addresses for one floating point number):

The two words MUST always be accessed together to ensure valid values.

Register 1 Low Word Register 2 High Word

Registers 3081 – 30a4 store Points 1 – C Data in this format Registers 4361 – 4384 store Points 1 – C Data in this format

Daniel’s Extension (1 register for one floating point number)

Register 1 Byte 0, Byte 1, Byte 2, Byte 3

Registers 7001 – 7012 store Points 1 – C Data in this format

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Chapter 7 Communications Interface

NOTE: Momentary coils activate the corresponding function every time a one is written to them.

Table 7-1 COILS 0XXX READ/WRITE (Use Functions 1, 5 or 15 to Access)

COIL # FUNCTION AND STATE

1 Alarm Relay Latched 0=Off 1=On

2 Alarm Reflash 0=Off 1=On

3 Alarm Fail Safe 0=Off 1=On

4 Alarm Open On Ack 0=Off 1=On

5 Reserved

6 Reserved

7 Reserved

8 Alarm Check 0=Enabled 1=Disabled

9 Span and Offset 0=Off 1=On

10 Reserved

11 ADC Frequency 0=60 Hz 1=50 Hz

12 Reserved

13 Reserved

14 Reserved

15 Reserved

16 Reserved

17 Ack Alarms (momentary)

18 Reserved

19 Chart Control 0=Chart Off 1=Chart On

20 Toggle Chart Speed (Momentary)

21 Scale Set 0=Set 1 1=Set 2

22 Learn Database (Momentary)

23 Reserved

24 Reserved

25 Chart Speed 0=Low 1=High

26 Auto Speed 0=Fix 1=Auto

27 - 63 Reserved

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Chapter 7 Communications Interface

Table 7-1 COILS 0XXX READ/WRITE (Use Functions 1, 5 or 15 to Access)

COIL # FUNCTION AND STATE

64 Clear All Points (Momentary)

65 Bypass/Activate Point 1 1=Bypass 0=Activate

66 Bypass/Activate Point 2 1=Bypass 0=Activate

67 Bypass/Activate Point 3 1=Bypass 0=Activate

68 Bypass/Activate Point 4 1=Bypass 0=Activate

69 Bypass/Activate Point 5 1=Bypass 0=Activate

70 Bypass/Activate Point 6 1=Bypass 0=Activate

71 Bypass/Activate Point 7 1=Bypass 0=Activate

72 Bypass/Activate Point 8 1=Bypass 0=Activate

73 Bypass/Activate Point 9 1=Bypass 0=Activate

74 Bypass/Activate Point A 1=Bypass 0=Activate

75 Bypass/Activate Point B 1=Bypass 0=Activate

76 Bypass/Activate Point C 1=Bypass 0=Activate

77 Reserved

78 Reserved

79 Reserved

80 Reset Point 1 (Momentary)

81 Reset Point 2 (Momentary)

82 Reset Point 3 (Momentary)

83 Reset Point 4 (Momentary)

84 Reset Point 5 (Momentary)

85 Reset Point 6 (Momentary)

86 Reset Point 7 (Momentary)

87 Reset Point 8 (Momentary)

88 Reset Point 9 (Momentary)

89 Reset Point A (Momentary)

90 Reset Point B (Momentary)

91 Reset Point C (Momentary)

92 Reserved

93 Reserved

94 Reserved

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Chapter 7 Communications Interface

Table 7-2 Status Inputs 1XXX Read Only (Use Function 2 to Access)

Register # FUNCTION AND STATE

1001 0=No Alarms Present 1=Alarm(s) Present

1002-1008 Reserved

1009 Digital Input 1

1010 Digital Input 2

1011 Digital Input 3

1012 Reserved

1013 Reserved

1014 Reserved

1015 Reserved

1016 Reserved

1017 Point 1 Status 1=Invalid

1018 Point 1 Status 1=Overflow

1019 Point 1 Status 1=Overrange

1020 Point 1 Status 1=T.C.B.O.

1021 Point 1 Status 1=Bypassed

1022 Reserved

1023 Reserved

1024 Reserved

1025 Point 1 Status 1=Alarm #1

1026 Point 1 Status 1=Alarm #2

1027 Point 1 Status 1=Alarm #3

1028 Point 1 Status 1=Alarm #4

1029 Point 1 Status 1=Alarm #5

1030 Reserved

1031 Reserved

1032 Reserved

1033 Point 2 Status 1=Invalid

1034 Point 2 Status 1=Overflow

1035 Point 2 Status 1=Overrange

1036 Point 2 Status 1=T.C.B.O.

1037 Point 2 Status 1=Bypassed

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Chapter 7 Communications Interface

Table 7-2 Status Inputs 1XXX Read Only (Use Function 2 to Access)

Register # FUNCTION AND STATE

1038 Reserved

1039 Reserved

1040 Reserved

1041 Point 2 Status 1=Alarm #1

1042 Point 2 Status 1=Alarm #2

1043 Point 2 Status 1=Alarm #3

1044 Point 2 Status 1=Alarm #4

1045 Point 2 Status 1=Alarm #5

1046 Reserved

1047 Reserved

1048 Reserved

1049 Point 3 Status 1=Invalid

1050 Point 3 Status 1=Overflow

1051 Point 3 Status 1=Overrange

1052 Point 3 Status 1=T.C.B.O.

1053 Point 3 Status 1=Bypassed

1054 Reserved

1055 Reserved

1056 Reserved

1057 Point 3 Status 1=Alarm #1

1058 Point 3 Status 1=Alarm #2

1059 Point 3 Status 1=Alarm #3

1060 Point 3 Status 1=Alarm #4

1061 Point 3 Status 1=Alarm #5

1062 Reserved

1063 Reserved

1064 Reserved

1065 Point 4 Status 1=Invalid

1066 Point 4 Status 1=Overflow

1067 Point 4 Status 1=Overrange

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Chapter 7 Communications Interface

Table 7-2 Status Inputs 1XXX Read Only (Use Function 2 to Access)

Register # FUNCTION AND STATE

1068 Point 4 Status 1=T.C.B.O.

1069 Point 4 Status 1=Bypassed

1070 Reserved

1071 Reserved

1072 Reserved

1073 Point 4 Status 1=Alarm #1

1074 Point 4 Status 1=Alarm #2

1075 Point 4 Status 1=Alarm #3

1076 Point 4 Status 1=Alarm #4

1077 Point 4 Status 1=Alarm #5

1078 Reserved

1079 Reserved

1080 Reserved

1081 Point 5 Status 1=Invalid

1082 Point 5 Status 1=Overflow

1083 Point 5 Status 1=Overrange

1084 Point 5 Status 1=T.C.B.O.

1085 Point 5 Status 1=Bypassed

1086 Reserved

1087 Reserved

1088 Reserved

1089 Point 5 Status 1=Alarm #1

1090 Point 5 Status 1=Alarm #2

1091 Point 5 Status 1=Alarm #3

1092 Point 5 Status 1=Alarm #4

1093 Point 5 Status 1=Alarm #5

1094 Reserved

1095 Reserved

1096 Reserved

1097 Point 6 Status 1=Invalid

1098 Point 6 Status 1=Overflow

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Monarch Instrument DataChart 2000 Modbus Protocol

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