How To: Set Up MDG Form For Data Acquisition
1. Start with a Modbus Data Group Form. You can create a new form or open an existing one.
To Create a new Modbus Data Group Form choosing File->New menu item, click the New Data Group
toobar button or type
the CTRL+N shortcut key combination.
To open an existing Modbus Data Group Form choosing File->Open menu item, click the Open Data Group
toobar button or type
the CTRL+O shortcut key combination and browse to/select the existing form (file name extension *.mdg).
2.Configure the Modbus Data Group Form to reflect the type of data to be acquired and displayed.
1. Set Device ID to the unit/slave ID of the device from which this form should acquire data. However note that
most Modbus TCP devices ignore this field and will respond to requests
3. Start data acquisition by checking the Start Polling checkbox or by clicking the right mouse button on the Data Display
Panel and choosing the Poll Device
with any device ID except zero.
2.Choose an appropriate Modbus Data Type reflecting the nature of data to be acquired from the device. This
information is generally published in the users manual as the address map
of your device. The Tester
decides on the Modbus Function Code to be used for the requests based on this parameter. Selecting an incorrect data
type will result in an Exception
Response from the device.
3.Choose the Start Address and Length fields to define the range of Modbus addresses for which data is to
be acquired. Select this range to reflect a logical group of addresses in your
device. While the form permits
configuration of a large number of addresses, it is suggested that all the addresses of interest be grouped and each
group be displayed in different MDG
forms. This makes it easier to view and analyse the acquired data. If any of the
addresses in the configured range does not exist in the device, an exception response is received from
causing data for existing Modbus addresses also to be unavailable.
4.Enter a duration (in milliseconds) for Poll Interval to set a periodic polling cycle. Setting too low a value can cause the
device to be overloaded with Modbus requests and setting too
The Start Address entered should be one more than the address as specified in the address map of the
device. This is because the Tester decrements the start address by one (1) before using it in encoding
Modbus packets as required by the Modbus specifications.
high a value can cause data to be sluggishly updated
on the display.
menu item in the context menu.
Verify that data acquisition is working fine.
If the address range and data type configured in the Data Group Form exist on the device, you should see data being displayed
on the form. If the form is unable to acquire data, it displays ???? in place of data.
The upper section of the Data Group Form shows a set of Poll Counters. If data acquisition is working correctly the
Polls counter must be equal to Resp (response) counter and the other remaining counters should not increment.
If you have multiple Data Group Forms open and would like to start or stop polling in all of them, you can use the
Start Poll All Data Groups
Stop Poll All Data Groups
toolbar buttons to do this.
You can create/open multiple Data Group Forms to view different sets of data. Each can acquire data at its own
Stability of a device's communication interface under heavy load conditions can be tested by setting a very low
value (<10ms) for Poll Interval so as to bombard the device with Modbus requests.
Incorrect setting of Modbus Data Type, Start Add and/or Length can cause the device to
respond with an Exception Response.