Value Maps are used with Slave drivers (drivers that provide data to another driver). Each Value Map, or Filtered Value Map (depending on the driver) is used by the Slave driver to map ClearSCADA database properties into a simple block of memory within the driver. The Slave driver can then use its native protocol to read the data from the Value Map or Filtered Value Map, and extract the value(s) that are required by its Master. The way in which the Slave driver accesses the data differs, depending on the protocol. For example, the Modbus Slave driver addresses registers by number.
A Value Map or Filtered Value Map can also perform extra processing on the values that it stores, such as scaling or type conversion. Filtered Value Maps can also store alarms and events in addition to ‘point’ values.
The values that are mapped by a Value Map or Filtered Value Map differ, depending on the application. Essentially, you can map any appropriate database value, such as the present state of a channel, or the result of a logic program, to a Value Map or Filtered Value Map. You can also map Variables, such as those representing internal values within the software, or Points that directly represent plant. (For more information on Points, see the ClearSCADA Guide to Core Point Configuration; for information on Variables, see Using Variables to Store Data Values.)
The type(s) of Value Map or Filtered Value Map that you can configure differs, depending on the type of driver. For further information,see Types of Value Map, and see the driver-specific documentation for information on the type(s) of Value Map or Filtered Value Map that are supported by the driver(s) on your system.
To create and configure a Value Map or Filtered Value Map, you need to:
- Add a New Value Map
- Edit a Value Map
- Specify the Map Size
- Specify the Number of Events that a Filtered Value Map can Store
(this step applies to Filtered Value Maps only) - Add an Entry to the Value Map
- Repeat step 5 for further variables, points, or other database values.
- Save the configuration.
To associate a Value Map or Filtered Value Map with a particular outstation, PLC or other Slave device, you need to specify the Value Map or Filtered Value Map on the relevant Outstation or Source Form (see the driver-specific documentation for further details).