Multi-Write Tags

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The MultiWrite tag will write predefined values to a list of selected tags upon triggering. This can be used to place a plant into a state of operation or to quickly shut a plant down in one step.

Trihedral technical support frequently receives requests for help with scripting when people want to send a control signal in response to a trigger. The response is almost always to use a Multi-Write tag in place of a script.

Reference Notes:

Up to 100 output and memory tags can be controlled by a single MultiWrite tag, with a defined value set to be written to each. The trigger for the write may be any of a manual button press, a tag that changes state from false to true, or an expression that evaluates to true.

Each value to be written will be checked to ensure that it is valid before it is written. Invalid writes will be ignored. All valid values will be written, regardless of whether they have changed since the last write.

Should 100 tags not be enough, it is possible for one MultiWrite tag to trigger another upon finishing its write sequence.

An event will be recorded in the event history whenever a MultiWrite is triggered.

If triggering a Digital Control or Digital Output with a pulse duration, use care that you do not attempt to send a pulsed zero.

Set Value Buttons and Multi-Write tags.

This tag will work with the Set Value Button Widget but support is limited:

  • Value to Write must be set to 1 in the widget for use with a Multi-Write tag. No other value will work.
  • Multi-write tags cannot act as feedback tags. To use Select Before Operate in the Set Value, a separate I/O tag must be configured as the feedback tag and used as the linked tag in the Execute / Cancel buttons.

MultiWrite properties Write List tab

The Write List displays the output or memory tags that will be written to, and controls what value will be written to each. The outputs will be written in the order in which they are displayed.

You can add or edit any tag in the list by clicking on a row. You must select a tag before configuring the value to be written to it.

The Tag and Value input fields will be activated when a row is selected, except that rows must be filled in sequence from #1. You cannot add a tag to row three before row two has been completed.

The grid displays the name and description of each tag selected to be written to. The Value column shows what will be written to each tag when the MultiWrite is triggered. The value may be any of a constant, an expression or another tag’s value. In the case where another tag’s value is to be written, that tag’s name will be display in the Value column.

Note that, the display may show a tag's Unique ID rather than its name when the tag is not selected. The description will always be shown for every tag, to help avoid confusion.

To add a tag to the list, select the next available row, then click on the Tag Browser button. Select or create an output tag. After you have specified the tag to write to, you can provide a value to write using the Value field.

To remove a tag from the list, select its row, then click on the X button in the lower-right corner of the window.

The arrow buttons below the grid may be used to move a selected row up or down in the list, thus controlling the order in which output tags are written to.

MultiWrite properties Activation tab

The Activation tab provides a way for MultiWrite tags to be controlled automatically.

Activation Trigger

Any tag or expression that will change from a false (0) to a true (1 or any non-zero number) can be used to trigger the write.

Privilege

Select a custom security privilege (Protect Pages and Output Tags) from this drop down to limit the operation of this control to only those operators who have been granted the matching security privilege.

Log an event on automatic multi-write

Selected by default. You can choose to not log events when multi-writes occur in response to the activation trigger. Choose this if you have a multi-write operation that triggers frequently.

An operator pressing the Multi-Write Button or Hotbox will always cause in a new event to be logged.