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Overview of Modbus TCP protocol

MindSphere supports the Modbus protocol for the MindConnect IoT2040, MindConnect Nano plugin and MindConnect Software Agent. You can select the protocol type Modbus TCP while adding a new data source in Asset Manager.

Note

Modbus configuration

The Modbus configuration view is only visible after a successful onboarding of the MindConnect IoT2040/Nano. The MindConnect Nano Version must be higher than V3.3.0.2.

The following picture shows the protocol selection in Asset Manager:

protocol-selection-asset-manager

Modbus

For more information about how to create a new data source see chapter Adding a data source and data points.

Modbus TCP data source parameter

In order to connect a Modbus TCP device, you need to select the Modbus TCP protocol and enter the following data source parameters:

Parameter Description
IP Address IP address of the Modbus device
Port Port number of the Modbus device (default: 502)

The following parameters are optional and can be adjusted for collecting data from slow Modbus devices:

Parameter Description
byteTimeout You can set the timeout interval between two consecutive bytes of the same message received from the Modbus device. If the delay between is longer than the given timeout, an error will be generated. Range: 500ms (default) … 2000ms
responseTimeout You can set the timeout interval used to wait for a response from the Modbus device. If the waiting before receiving the response is longer than the given timeout, an error will be generated. Range: 500ms (default) … 60000ms
responseSuspensionTime If a byte timeout or a response timeout was detected, then this waiting time is added before the next request is started. During this time any response from the Modbus device will be flushed. Range: 0ms … 45000ms. (default: 1000ms)
requestDelay You can set the time between the response from the Modbus device and the next request to this Modbus device. Range: 0ms (default) … 10000ms

Modbus TCP data point parameter

In order to collect the data of your Modbus TCP device, you must add new data points.

The following picture shows the data point parameter window:

data-point-parameter-window

The following table shows the parameter of the Modbus RTU data point window:

Parameter Description
Data Type Data type supported by backend (e.g. INT).
Function Type Function type - depends on the type of the data (see manual of the Modbus device). 1: Read Coils, 2: Read Inputs, 3: Read Holding Registers, 4: Read Input Registers. Currently function codes 1..4 are supported.
Slave Number Address/Slave number of the Modbus device.
Start Address Start address (offset) of the data.
Quantity Quantity of data to be read.
VariableType You can choose the following variable types of the Modbus data to be read: 1: char, 2: unsigned char, 3: short, 4: unsigned short, 5: long , 6: unsigned long , 7: float, 8: double, 9: ascii-text
Real Type Real type - determines, if the registers of real values have to be processed in reversed order. 0: Normal order, 1: Reversed order, 2: Byte swap order, 3: Word swap order, Real types 2 and 3 are available from V03.04.02.01.
Response Address Offset Offset of the data to return in register units.
Response Quantity Quantity of the returned data. Only for string data a value greater than 1 is supported.

Note

TCP Gateway slave number

If you are using a TCP Gateway, you must select the appropriate slave number for the configuration of the data points.

Addressing:

The information is stored in the Modbus Slave device in 4 different tables. 2 tables store on/off discrete values (coils) and two store numerical values (registers). Each coil is 1 bit long and assigned a data address between 0 and 65535. Each register has the size of 1 word(16 bits/ 2 bytes) and has a data address between 0 and 65535.

Coil/ Register numbers Data addresses Function type Table name
1-9999 0 to 65535 1 Read Coils
10001-19999 0 to 65535 2 Read Inputs
30001-39999 0 to 65535 4 Read Input Registers
40001-49999 0 to 65535 3 Read Holding Registers

Coil / register numbers can be considered as location names since they do not appear in the configuration. The Data Addresses (Start Address) are used in the configuration.

Data Types:

MindSphere data types:

Data type Length Data range
BOOLEAN 1 bit True to False
INT 4 bytes −2147483648 to 2147483647
LONG 8 bytes −9223372036854775808 to 9223372036854775807
DOUBLE 8 bytes -9.9999999999999999999999999999999999999E+125 to
9.9999999999999999999999999999999999999E+125
STRING 1 - 255 bytes

Modbus data types:

Data type Length Data type number Data range
char 8 bits 1 -128 to 127
unsigned char 8 bits 2 0 to 255
short 16 bits 3 -32768 to 32767
unsigned short 16 bits 4 0 to 65535
long 32 bits 5 −2147483648 to
2147483647
unsigned long 32 bits 6 0 to 4294967295
float 32 bits 7
double 64 bits 8
ascii-text 8 bits / char 9

Examples:

Example Data type Function type Start address Variable type Response Address Offset Response Quantity
Reading the first Holding int Read Holding 0 unsigned 0 1
Register, number 40001, has Registers short
the start address 0. or short
VariableType: 4 or 3 (unsigned int Read Input 1 unsigned 0 1
short or short)Reading the Registers short
second Input Register, number or short
30002, has the start address 1.
Reading a float (32 bits) from double Read Input 107 float (reads 0 1
Input Register 30108 / 30109, Registers two registers)
has the start address 107.
Reading a string. This example string Read Holding 5 unsigned 0 2 (registers)
describes to read four letters Registers short
from register 400006 and
400007. Each register
contains two characters.
Reading a Boolean from the Boolean Read Holding 10 unsigned 0 1
Holding Register 40011, has Registers short or short 0 1
the start address 10. If the
hole Holding Register has the
value 0 then it is displayed
as 0. If one bit(or more) has
the value 1 then it will be
displayed as 1.

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Last update: May 19, 2022