When you assign I/O to a supported function block the data transfer is initiated automatically when all of the following conditions are met:
A signal exists
The signal is enabled.
The signal name matches the function block parameter name
There is at least one parameter in the signal with the same name as the name of a parameter in the assigned function block.
The parameter is exposed for update (Class Based module instances)
The parameter's values need to be updated.
When you assign I/O from DeltaV Explorer or Control Studio, the Confirm Signal Transfer dialog appears and you can choose to accept or reject the transfer. When the I/O assignment is initiated from a batch process such as the Excel Data Manager Save command, a standard import of an fhx file, or Bulk Edit your only control of whether the data is transferred or not is enabling or disabling the signal.
Data transfer is controlled by the enabled property of each signal. In the Excel worksheet it is the cell at the intersection of the signal row and enabled column. If the value in this cell is TRUE then data can be transferred to the block that an I/O signal is assigned to. That is, SPI is the master data source. If the cell value is FALSE then data is not transferred from the signal to the assigned block. That is, DeltaV software's function block configuration is the master data source.
Whenever you retrieve data from SPI all signal enabled columns are set to TRUE to enable data transfer because by default SPI is the master data source.
When you Publish to SPI the enabled cell is set to FALSE. This disables data transfer, because by implication the DeltaV database is the master data source. In addition, Publish automatically updates signal data from module configurations for supported function blocks which are assigned to supported I/O.
Analog input, Pulse Counter Input, and PID controller blocks have alarm and limit capability. If you define alarms in SPI this property (the intersection of the signal parameter row containing ALM_ENABLE with the value column) is set to TRUE automatically by Retrieve from SPI. To disable transfer of alarms to function blocks set this property to FALSE in the Excel worksheet.
The signal definition within a DST (or fieldbus function block) must match the signal name in the function block it is assigned to. That is, assigning an AI signal with an AI definition name to an AI function block initiates data transfer if the other conditions are satisfied, but assigning an AI signal with an AI definition name to a PID function block the data is not transferred.
On retrieve, the signal definition is created automatically based on the SPI signal type for conventional and HART signals or the function block in the device that the signal is assigned to. On publish, a compatible signal is created for each I/O that is assigned to a supported function block.