Modbus Communication API

Overview

Basic Overview

• This describes how to set up Modbus communication for the softMC, and how to generate softMC scripts to handle Modbus communication.
• It is assumed you are familiar with the principles of Modbus communication, although some of them will be described in this page.
• It is also assumed your are familiar with the softMC, ControlStudio and MC-Basic programming.

Modbus Communication Background

• A Motion Controller (MC) can act as a server (slave), a client (master) or both at the same time.
• Each MC connection (TCP/RTU) can be used either as a server component (if the connection is used by the MC’s server-side) or as a client component (if the connection is used by the MC’s client-side).
• Each component has its own parameters that defines it.
• When the MC acts as a server, all server components share the same memory address space, thus acting as one server with multiple connections.
• Each server (slave) on a Modbus network has its own deviceID, which is a number between 1 and 247.

The Modbus server registers

• There are 4 types of registers in the Modbus Server address space:
  1. Bits (1-bit registers)
  2. Input Bits (1-bit READ-ONLY registers)
  3. Holding Registers (16-bit registers)
  4. Input Registers (16-bit READ-ONLY registers)
• Servers can read and write their own address space.
• Clients can read and write a remote server’s address space.

Getting Started

In order to get started in using the Modbus features:

1. Download the required files, according to your system's type:
   1. Required files for modbus_X86.ZIP.
   2. Required files for ARM systems.
2. Using the ControlStudio File Manager, Upload the following files to your MC:
   1. mb_x86.O (for X86 Systems) / mb_armA9.O (for ARM Systems)
   2. Modbus.lib
   • Notice: From now on, in our examples, we'll use the X86 configuration.
     
3. Access the file CONFIG.PRG and modify the program by adding the following two lines:

   Program
   	Oload mb_x86.O
   	Load modbus.lib
   ...
   ...
   End Program

4. Upload CONFIG.PRG to the softMC.
5. Use the ControlStudio Terminal to enter the following:

   reset all
   ?tasklist

   The system's response:

   GlobalLibraryName=MODBUS.LIB

   This indicates that library MODBUS.LIB has been loaded globally.
   
6. That's it! You're now ready to configure the Modbus system.

Initializing a Modbus Server

To initialize the Modbus server address space, call:

?init_multi_server([bits],[input_bits],[holding registers],[input_registers])

• The function prints "success" and returns 0 on success, or return an error code on failure.
• Notice:
  1. This is NOT required when softMC does not run a modbus server.
  2. You can call this method only if no servers are running.

Error codes:

Error	Meaning
-1	Memory allocation failure.
-2	Some servers are still running and using an already mapped address space.
-3	Failed to create a modbus mapping.

Server Components

Adding server components

• Each time you'll add a component, you will receive a handle, which is the component's identifier (for later use).
• It is best to keep this handles in variables inside your program.

Creating a TCP server component

handle = mb_tcp_server_create([port],[deviceID])

• This opens a TCP connection to the server on port [port] with deviceID [deviceID], and starts the created server immediately.
• Returns a handle on success, or an error code on failure.

Error codes:

Error	Meaning
-1	Server address spaces isn't initialized yet, please call "init_multi_server(...) and try again.
-2	Failed to create main socket.
-3	Failed to connect.
-4	Failed to create server thread.

Creating an RTU server component

handle = mb_rtu_server_create([type],[port],[baudrate],[data bits],[stop bits],[parity],[deviceID])

• This opens an RTU connection with the given parameters, and starts the created server immediately.
• Returns a handle on success, or an error code on failure.

Error codes:

Error	Meaning
-1	Server address spaces isn't initialized yet, please call "init_multi_server(...) and try again.
-2	Invalid device string.
-3	Invalid parity.
-4	Failed opening RTU.
-5	Failed allocating query buffer memory.
-6	Failed to set RTU mode.
-7	Unable to connect.
-8	Failed to create server thread.
-9	The device is already in use by another system component.

Stopping Server Components

Stopping a specific server component

You can stop a specific server component by passing its handle to:

result = mb_server_stop([handle])

• Given a handle, this will stop and free the memory of the appropriate server component.
• Returns 0 on success, -1 on failure.

Stopping all server components

You can stop all server components with a single call to:

result = mb_server_stop_all

This function will:

• Stop and free all server components.
• Free the shared address space.
• Return 0 on success, -1 on failure.

Client Components

Adding client components

• Each time you'll add a component, you will receive a handle, which is the component's identifier (for later use).
• It is best to keep this handles in variables inside your program.

Adding a TCP Client component

handle = mb_tcp_client_create([ip],[port])

• This will opens a TCP connection to the client on the given ip and port, and start the client immediately.
• Returns a handle on success, -1 on failure.

Adding an RTU Client component

handle = mb_rtu_client_create([type],[port],[baudrate],[data bits],[stop bits],[parity])

• This will open an RTU connection to the client with the given parameters, and start the client immediately.
• Returns a handle on success, -1 on failure.

Stopping client components

A specific client can be stopped by calling:

result = mb_client_stop([handle])

• Given a handle, this will stop and free the memory of the appropriate client component.
• Returns 0 on success, -1 on failure.

Reset the Modbus System

Sometimes, a user may wish to stop all server and client components at once, and reset the Modbus system (for example, when a user want to initialize a different Modbus system). To do that, call:

result = mb_reset

This function:

• Stops all running servers and clients.
• Frees their memory.
• Frees the shared address space.
• Reset the handle counter.
• Returns 0 on success, -1 on failure.

Reading and Writing

• Servers can read and write their own address space.
• Clients can read and write a remote server’s address space.
• Therefore, Servers and clients use different functions to read/write data from the address space.

Server Components

Reading

• The following functions read variables from the different types of registers and return them.
• When a read error occurs, the functions will write [function name] + "ERROR" + [error code] in the Message Log.

Reading from Holding registers

Val = MB_SERVER_READ_REG_LONG([index], [byte_swap], [word_swap])
Val = MB_SERVER_READ_REG_SHORT([index], [byte_swap])
Val = MB_SERVER_READ_REG_FLOAT([index], [byte_swap], [word_swap])
Val = MB_SERVER_READ_REG_DOUBLE([index], [byte_swap], [word_swap], [long swap])

Reading from Bits registers

val = MB_SERVER_READ_BIT([index])

Reading from Input registers

Val = MB_SERVER_READ_INREG_LONG([index], [byte_swap], [word_swap])
Val = MB_SERVER_READ_INREG_SHORT([index], [byte_swap])
Val = MB_SERVER_READ_INREG_FLOAT([index], [byte_swap], [word_swap])
Val = MB_SERVER_READ_INREG_DOUBLE([index], [byte_swap], [word_swap], [long swap])

Reading from Input Bits registers

 val = MB_SERVER_READ_INBIT([index])

Valid Parameters

Parameter	Valid Input
Index	From 0 to the number of registers available.
Byte_swap	1 or 0 (True/False)
Word_swap	1 or 0 (True/False)
Long_swap	1 or 0 (True/False)

Writing

• The following functions write data into the different types of registers.
• When a write error occurs, the functions will write [function name] + "ERROR" + [error code] in the Message Log.

Writing to holding registers

Val = MB_SERVER_WRITE_REG_LONG([index],[new value],[byte swap], [word swap])
Val = MB_SERVER_WRITE_REG_SHORT([index],[new value],[byte swap])
Val = MB_SERVER_WRITE_REG_FLOAT([index],[new value],[byte swap], [word swap])
Val = MB_SERVER_WRITE_REG_DOUBLE([index],[new value],[byte swap], [word swap], [long swap])

Writing to Bits registers

val = MB_SERVER_WRITE_BIT([index],[new value])

Writing to Input registers

Val = MB_SERVER_WRITE_INREG_LONG([index],[new value],[byte swap], [word swap])
Val = MB_SERVER_WRITE_INREG_SHORT([index],[new value],[byte swap])
Val = MB_SERVER_WRITE_INREG_FLOAT([index],[new value],[byte swap], [word swap])
Val = MB_SERVER_WRITE_INREG_DOUBLE([index],[new value],[byte swap], [word swap], [long swap])

Writing to Input Bits registers

val = MB_SERVER_WRITE_INBIT([index],[value])

Valid Parameters

Parameter	Valid Input
Index	From 0 to the number of registers available.
New value	The value to write, must be from the appropriate type.
Byte_swap	1 or 0 (True/False)
Word_swap	1 or 0 (True/False)
Long_swap	1 or 0 (True/False)

Error codes

Error	Meaning
-1	Invalid index.
-2	Local server's address space isn't mapped yet.
-3	Failed to catch the register mutex.
-4	Failed to release the register mutex.

Client Components

Reading

• The following functions read variables from the different types of registers in a REMOTE modbus server.
• The read value is inserted into an existing variable from the appropriate type (long/double).
• The functions return 0 on success or an error code (not 0) on failure.

Reading from Holding registers

Val = MB_CLIENT_READ_REG_LONG([handle],[deviceID],[addr],[dest ptr])
Val = MB_CLIENT_READ_REG_SHORT([handle],[deviceID],[addr],[dest ptr])
Val = MB_CLIENT_READ_REG_FLOAT([handle],[deviceID],[addr],[dest ptr])
Val = MB_CLIENT_READ_REG_DOUBLE([handle],[deviceID],[addr],[dest ptr])

Reading from Bits registers

val = MB_CLIENT_READ_BITS ([handle],[deviceID],[addr],[num of bits],[dest arr ptr])

Reading from Input registers

Val = MB_CLIENT_READ_INREG_LONG ([handle],[deviceID],[addr],[dest ptr]) 
Val = MB_CLIENT_READ_INREG_SHORT([handle],[deviceID],[addr],[dest ptr])
Val = MB_CLIENT_READ_INREG_FLOAT([handle],[deviceID],[addr],[dest ptr])
Val = MB_CLIENT_READ_INREG_DOUBLE([handle],[deviceID],[addr],[dest ptr])

Reading from Input Bits registers

val = MB_CLIENT_READ_INBITS ([handle],[deviceID],[addr],[num of bits],[dest arr ptr])

Valid Parameters

Parameter	Valid Input
Handle	The client's unique identifier (received on client creation).
DeviceID	The remote server(slave)'s device ID.
Addr	The index of the register to read from.
Num of bits (Reading bits)	The number of bits to read.
dest ptr / dest arr ptr	The variable to store the read data. When reading bits, this must be an array of longs in the appropriate size (>= Num of bits).

Writing

• The following functions write data from existing variables to the different types of registers in a REMOTE modbus server.
• The functions return 0 on success or an error code (not 0) on failure.

Writing to Holding registers

Val = MB_CLIENT_WRITE_REG_LONG([handle],[deviceID],[addr],[src ptr])
Val = MB_CLIENT_WRITE_REG_SHORT([handle],[deviceID],[addr],[src ptr])
Val = MB_CLIENT_WRITE_REG_FLOAT([handle],[deviceID],[addr],[src ptr])
Val = MB_CLIENT_WRITE_REG_DOUBLE([handle],[deviceID],[addr],[src ptr])

Writing to Bits registers

val = MB_CLIENT_WRITE_BIT([handle],[deviceID],[addr],[src ptr])

Valid Parameters

Parameter	Valid Input
Handle	The client's unique identifier (received on client creation).
DeviceID	The remote server(slave)'s device ID.
Addr	The index of the register to start writing to.
src ptr	The variable that stores the data to be written. This must be a variable from the appropriate type.

Reading and Writing Summary

Modbus Configurator

The Modbus Communication Scripts Generator (Modbus Configurator) is a tool that allows you to map your softMC application variables to Modbus tags.

Note: Tag access is defined from the HMI perspective. In other words:

• Read Access variables are written by the softMC to the Modbus address space.
• Write Access variables are read by the softMC from the Modbus address space.

You can define whether a variable has Read Access (meaning it is read by the HMI/PLC), or Write Access (meaning it is written by the HMI/PLC). Currently, it is not possible to define a variable as having both Read Access and Write Access. However, all Write Access variables can be written once by the softMC upon system startup by a special routine that is generated in HMIMBMAP.LIB (see section below).

The MCMBConfigurator creates three files:

• HMIMBMAP.LIB and HMIMBMAP.PRG files are MC-Basic scripts that are used to start a softMC task. These are default file names, which you can change, but must retain the 8.3 format. This task cyclically and indefinitely reads/writes Modbus tags according to access type.
• A .CSV format file that can be used by an HMI development environment, such as JMobile Studio or Indusoft, to automatically import Modbus tags. You define the HMI development environment by selecting various Python scripts that will generate the .csv file.

Mapping Variables

Note: Variables destined to be mapped to Modbus tags must be defined as global variables by the Common Shared declaration.

1. In order to map the variables, the program must be loaded in the softMC.

2. Start the Modbus Configuration: from the ControlStudio toolbar, select Tools, and then Modbus Configurator…

The Modbus Configurator windows opens.

3. Click Connection, and select Setting.

The setting dialog box opens, with fields showing the following (default) settings:

• Modbus offset: Used to start the mapping from an address other than zero.
• Script file name: A Python script that generates the product files. Different scripts create different .csv files.
• Output LIB, Output Prog, HMI CSV file name: Used to define target file names.

Note: The softMC file names must be UPPERCASE and in 8.3 format.

• MC IP address: Used to set the IP address of your softMC.

Make any necessary changes in the Settings dialog box. Then click Connection, and then Connect.

Once the Modbus Configurator is connected to softMC it gets updated with the complete list of all the global variables. Double-clicking on variables automatically maps them to Modbus tags in consecutive order. The automatic Modbus address and data type are displayed in the table.

If a mapped variable is defined as CONST, its access type is automatically set to Read. In such instances the access type cannot be changed. Read Access variables are read only by the HMI; therefore the softMC only writes them to the Modbus address space.

A variable that is not defined as CONST automatically appears as Write Access. Double-click on the access type to toggle the variable between Read Access and Write Access, and thus determine whether the variable will be read or written by softMC.

Generating and Using Scripts

After you are done mapping variables and defining the access types, a snapshot of the current configuration must be saved in order to generate the Modbus-handling scripts.

1. Click Files, and then Save As.

The mapping is saved in an .mbas file.

If you makes changes after saving the .mbas file, the MBAS file indicator in the status bar will light up.

2. To generate the product files, click Generate.

The Log windows will display Success messages.

The product files were created in the target folder you chose when saving the .mbas file.

The files HMIMBMAP.LIB and HMIMBMAP.PRG will automatically open in ControlStudio.

Using the Modbus-Handling Scripts

1. Using the ControlStudio File Manager, copy HMIMBMAP.LIB and HMIMBMAP.PRG to the softMC.

Note: Before these files can be loaded and used, your application must be loaded, and all mapped variables must exist in the softMC memory.

1. Using the ControlStudio Terminal, load the library HMIMBMAP.LIB:

Load HMIMBMAP.LIB

Since HMIMBMAP.PRG imports this library it must not be loaded globally. This code can be executed wherever is convenient.

2. Verify that the library was loaded successfully:

?tasklist

3. Start the Modbus communication task by loading the program:

Load HMIMBMAP.PRG

HMIMBMAP.PRG is defined as Program Continue, therefore it starts automatically after it is loaded and it does not require an explicit StartTask command.

Of course, HMIMBMAP.PRG can be loaded and executed only after HMIMBMAP.LIB is loaded. Therefore, you should add the following code to AUTOEXEC.PRG or wherever is convenient:

Load HMIMBMAP.LIB
Load HMIMBMAP.PRG

HMIMBMAP.PRG Explained

The code:

import HMIMBMAP.LIB
Program Continue
	dim retVal as long = 0
	retVal = Init_Modbus
	while 1
		retVal = Read_Modbus_Registers
		retVal = Write_Modbus_Registers
		sleep 1
	end while
End Program

The functions Init_Modbus, Read_Modbus_Registers and Write_Modbus_Registers are implemented in HMIMBMAP.LIB, which is automatically generated by a Python script.

The function Init_Modbus starts the Modbus server and then writes to the Modbus address space all the Write Access Variables (i.e., all the variables read by the softMC from the Modbus address space). This feature allows you to setup the system to start with an initialized Modbus address space before the HMI/PLC connects to it. The HMI/PLC can read the address space and initialize itself accordingly.

The functions Read_Modbus_Registers and Write_Modbus_Registers are invoked cyclically and indefinitely. Read_Modbus_Registers reads all the tags that are written by the HMI/PLC and updates the Write Access variables with new values, while Write_Modbus_Registers does the opposite.

4 HMI IDEs and .CSV Files

Each line in the .csv file generated by the MCMBConfigurator file holds data about a single variable, such as Modbus address or data type.

This data can be used by an HMI IDE to import Modbus tags and associate them with HMI functionality.

Different manufacturer IDEs use different .csv formatting; therefore, various Python scripts are used to create the specific .csv files suitable for a particular manufacturer IDE.

JMobile Studio

Python script: JMobile_csv.py

Default target .csv file name: JMobile_HMI.csv (user-definable)

To import tags, perform the following procedure in JMobile Studio.

Define Protocol

1. In the ProjectView pane, select Protocols.

2. Click the blue + sign.

3. From the list, select Modbus TCP.

4. In the Modbus TCP configuration window, define:

IP Address: Set the IP address of your softMC.

PLC Models: Select Generic Modbus (0-based), meaning the softMC Modbus server starts addressing tags from 0.

Click OK.

Import Tags

1. In the ProjectView pane, select Tags.

2. From the list, select Modbus TCP protocol defined previously.

3. Click the Import Tags button.

4. Open the generated file JMobile_HMI.csv.

5. Select the tags you want to add to your project, and click the Import tags button.

AdvancedHMI

AdvancedHMI is an open source project (http://www.advancedhmi.com/), which is downloaded as a Visual Basic project. You can then open the project, add widgets, compile, and run it.

1. Drag and drop ModbusTCPCom into MainForm.vb [Design].

2. The driver appears the bottom of the screen (circled in green).

Click the driver, and then use the Properties pane (circled in red) to setup the IP address of the Modbus server.

For example, drag and drop DigitalPanelMeter and MomentaryButton into MainForm.vb [Design].

3. For both widgets, use the Properties pane to set the Modbus address that is associated with the variables from the softMC application.

Note:

MC Modbus server addressing starts from 40000.

AdvancedHMI Modbus client addressing starts from 40001.

Prefix the address with the letter L.

4. Save the project (Ctrl+S).

5. Build the project (Ctrl+Shift+B).

6. Run the project (F5).