Using
Modbus
 Communications

The AADvance controller supports
Modbus®
communications and can act as a
Modbus
 master or
Modbus
 slave. A
Modbus
 master can have
Modbus
 master slaves. The AADvance controller can use serial or Ethernet ports for
Modbus
 communications.
TIP: The AADvance controller does not support the
Modbus
 ASCII protocol.
The
Modbus
 functionality implemented by the AADvance controller meets this standard:
Modbus
 Application Protocol Specification, version 1.1b
. December 2006. The
Modbus
 Organization.
To use
Modbus
 communications,
Modbus
 variables for the controller must be mapped. These variables are then used by
Modbus
 slaves,
Modbus
 masters, and
Modbus
 master slaves. When mapping variables, these are mapped as the following types:
  • Coils
  • Discrete Inputs
  • Input Registers
  • Holding Registers
    TIP: 64-bit variables are not supported in Modbus communications. Use 32-bit variables.
The
Modbus
 mapping includes the following properties:
Name
The name of the variable.
Data Type
The data type of the variable.
Direction
The direction of the variable.
Base Address
The base address of the variable. Possible values range from 1 to 65536; the default starting address value is 1.
Allow
Modbus
 Write
For Coils and Holding Registers, indicates whether data can be copied from the
Modbus
 master to the slave device.
Modbus
 uses a numeric addressing scheme to move data between devices. AADvance controllers provide a dedicated area for each of the four variable types. The original
Modbus
 standard defines the address field as a four-digit field with a prefix relating to the variable type. The crosshatch areas in the following example display how the original-style, five-digit
Modbus
 addresses (for example, a holding register at 40,001) are related to the AADvance memory map.
cmv_umc
The base addresses used for
Modbus
 data transfer listings start at one. The first variable network address of the AADvance controller is 1 and the first coil is 00001.
When managing
Modbus
 variables, perform these tasks in the
Modbus
 element:
Task
Procedure
Add a
Modbus
 variable
  1. In the
    Communication View
    , double-click the
    Modbus
    element.
    The
    Communication
    property page displays.
  2. In the property page, select the tab in which to map the variable, and then click
    Add Variable
    .
  3. From the
    Variable Selector
    , locate the variable to use for the
    Modbus®
    mapping, and then click
    OK
    .
  4. In the property page, enter the required value for the
    Base Address
     property.
  5. For Coils and Holding Registers, set the
    Allow
    Modbus
     Write
     property to the required value.
    TIP: If the project contains two or more controllers, simulating the project and then stopping the simulation causes the
    Communication
    View
     to be read-only. To edit
    Modbus
     variables after stopping the simulation, close and then reopen the project.
Renumber base addresses of
Modbus
 variables
Renumber the base addresses of
Modbus
 mapped variables. Base address values are assigned in the order of appearance in the list of mapped variables. Base addresses range from 1 to 65536; the default starting address value is 1.
TIP: Manually modify the base address of
Modbus
 variables to the required values.
In the
Communication View
, double-click the
Modbus
element.
The
Communication
property page displays.
  1. In the property page, select the tab having the required mapped variables.
  2. In the list of mapped variables, select and right-click the variables to renumber, and then click
    Renumber
    .
  3. In the
    Renumber Addresses
     dialog box, specify the value to use for the base address of the first selected variable, and then click
    OK
    .
Allow the
Modbus
 write attribute for
Modbus
 variables
Allow the
Modbus
 write attribute for coils and holding registers mapped variables.
  1. In the
    Communication View
    , double-click the
    Modbus
    element.
  2. In the
    Communication
    property page, select the tab having the required mapped variables.
  3. In the list of mapped variables, select and right-click the variables for which to allow the
    Modbus
     write attribute, and then click
    Allow
    Modbus
     Write
    .
Disable the
Modbus
 write attribute on
Modbus
 variables
Disable the
Modbus®
write attribute for mapped variables. The
Modbus
 write attribute is only available for coils and holding registers variables.
  1. In the
    Communication View
    , double-click the
    Modbus
    element.
  2. In the
    Communication
    property page, select the tab having the required mapped variables.
  3. In the list of mapped variables, select and right-click the variables for which to disable the
    Modbus
     write attribute, and then click
    Disable
    Modbus
     Write
    .
Remove
Modbus
 variables
  1. In the
    Communication View
    , double-click the
    Modbus
    element.
  2. In the
    Communication
    property page, select the tab from which to remove mapped variables.
  3. In the list of mapped variables, select the variables to remove, and then click
    Remove Selected
    .
Delete a
Modbus
 object
  • In the
    Communication View
    , right-click the
    Modbus
     slave, master, or master slave, and then click
    Delete
    .
Also configure
Modbus
 Master and Slave protocols for use in the communication services for controllers.
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