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Generic Modbus

Generic Modbus allows Modbus registers to be turned into Smart Objects. This means that individual points can be shown in the user interface. It also allows for data logging and alarm thresholds to be set.

Generic Modbus points are created using the Modbus Discover Wizard.

To set up Modbus, go to Discovery | MODBUS Discover.

  1. Select Custom Modbus Control (Using Templates), and then click Next.

  1. Select the slave and unit numbers, and then click Next.

  1. Enter a unique name for the device, and then click Next.

  1. Select a predefined template from the WEMS Templates folder or a custom template from the Custom Templates folder, and then click Next.

To create a new custom template, do not select any option on this screen and instead click Next. The following screenshots show the creation of a custom template.

  1. Select a room for the Modbus slave, and then click Next.

  1. Use the bottom half of the following screen to enter settings for the register types relevant to the Modbus device.
ClosedDefinitions of settings
Name Description
Description The name of the register
Data Type The type of the register: Integer, Float, Bit or Text. To match the way regular Objects are handled, Integers are treated as digital inputs, Floats are treated as analog inputs, Bits are treated as relays/digital outputs, and text is treated as text
Polling Frequency The polling interval of the register for the value to be read, e.g. a return air temp should be read every 1 (the minimum) poll of the registers by the Modbus process whereas unimportant information such as AHU Manufacturer should be set to 10 (the maximum) polls by the Modbus process
Hysteresis The number the value must change by to display a new value
Scale The divisional scale to achieve the correct value, e.g. if outside air temp reads over Modbus as 165 it should be given a scale of 10 to show the value 16.5
Translation Method The calculation to get the desired value from the Modbus data packet
Start Bit At which part of the Modbus packet to start reading from (generally 0)
Bit Count Used in tandem with Start Bit. From the start bit, count the number of bits to get the value
Byte Order Determines the order in which to read the bytes
Offset How much the value needs to be changed by to equal 0
Modicon Read Address The modicon read address of the register. The wizard will not allow the same register to be selected twice
Modicon Write Address The modicon write address of the register. The wizard will not allow the same register to be selected twice
Modal Tick to automatically write the desired value every poll regardless of whether the value is already set (used mainly for heartbeat)
Dispatch Events Tick to allow the register to send values to be logged in the database
Access Rights Set the register to read-only or read-write mode
Icon The icon to be used to represent the register. There is an option to use generic Modbus icons called 'GM' of each type (analog, digital or relay)
  1. When a given point has been configured, click Add to add it to the table in the top half of the screen.
  2. Repeat the process to add multiple points.
  3. Once all points have been added, enter a name in the Template Name field, and then click Next.

  1. Tick the box to represent Modbus points as Objects, and then click Next.

The following page allows the Objects to be customised.

  1. Select an Object and define the settings for its type, location, hysteresis and visibility.
  2. Click Update to confirm any changes to the Object or use the relevant Update All buttons to update every listed Object with the same settings, and then click Next.

  1. The Modbus points will now be created. Click Next to continue.

  1. Finally, click Finish to exit the wizard.

If the configured points were set to 'visible' in the wizard, they will be displayed on the Floorplan.

WEMS User Guide version 4.0 20150130.
This guide relates to features up to and including 1.18.0.3