Define Communications and Status Reporting

The configuration settings for a
Modbus®
master include communications and status reporting. When configuring a
Modbus
 master, define these properties:
Property
Description
Communications Link
The physical communications link to use for this
Modbus
 master device. Select
Ethernet
or
Serial
. For
Ethernet
, enter the IP address of the
T8151 Communications Interface
 port to use, and the TCP/IP port number (1000 by default). For
Serial
, choose the port to use. The serial parameters are defined in the
T8151 Communications Interface
 configuration screen.
Timeout
The communications timeout for the link indicating how long to wait before deciding that a slave device is not responding. Every
Modbus
 master and associated slave in the system can have a control and status register. These registers enable controlling each device and retrieving status information via the application.
Communications Control
The
Modbus
 address of the application variable to control the master device. If the application does not control the master device, leave unchecked. These are the valid values for a slave control holding register. Invalid values result in the inactive state.
Use different
Modbus
 addresses for all control and status holding registers, and control variable coils.
State
Value
Description
Inactive
0
Set link inactive, stop communications, set slaves unavailable
Standby
1
Set link active but do not transfer data
Active
2
Set link active and transfer data
Status Reporting
The
Modbus
 address of the application variable to report the status of the communications link to the application. If status reporting is not required, leave unchecked. These are the valid values for a master status holding register.
Use different
Modbus
 addresses for all control and status holding registers, and control variable coils.
State
Value
Description
Healthy
0
Link is active, no errors reported
Initializing
1
Link is not yet established or has failed, slaves are unavailable
Error
2
Software error in communications module
To define communications and status reporting for a
Modbus
 master
  1. Click the
    Configuration
    tab.
  2. In the
    Communications Link
     group, select the type of port and define the properties:
    • Ethernet
    • Serial
  3. In the
    Timeout
    area, specify a timeout delay (in milliseconds).
  4. (optional) In the
    Applications Interface
     area for
    Slave Control
    , select
    Application Controls
    , and then indicate the
    Modbus
     address for the communications control variable to enable the application to control communications for the
    Modbus
     master.
  5. (optional) In the
    Applications Interface
     group for
    Status Reporting
    , select
    Report Status
    , and then indicate the
    Modbus
     address for the status reporting variable to report the status of the communications link to the application.
  6. Click
    Save
    .
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