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The data flow diagram for the ISaGRAF unit is shown below. Compare this with the data flow diagram for an external device (Master/Slave Channel Functional Elements196653).
- The Internal Channel generates a poll request based on its Scan Table.
- The ISaGRAF Protocol task (Field Unit definition) looks up the requested poll in its Poll Table and sends the defined command to the internal ISaGRAF RTU.
- The response from ISaGRAF is processed and validated
- The ISaGRAF data is then stored into the RTDB. This polling cycle continues based on the timing and sequence defined in the ACE configuration for the Internal Channel. The RTDB typically only contains the last known value for each data point in its register locations.
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In addition to the special handling of the internal ISaGRAF RTU, the Internal Channel includes other child elements that provide special features within the system. These are the Virtual RTU, Status RTU, Segment RTU, and Internal Master. These are all connected to the Internal Channel using a "Null Circuit," which is simply a placeholder to preserve the normal Channel-Circuit-Field Unit structure. These types of field units are briefly explained here.
The Virtual RTU provides a data repository (RTDB) for internal storage of data, which is not connected with any external field device or ISaGRAF unit. 
The Status RTU is another type of Virtual RTU, that can be used for storing data, but it has an additional purpose. When the RediGate is configured to poll one or more Field Devices using one or more Master Channels, there is some status information for each device such as poll count, current failed/good communication status, etc. These statistics for a whole set of Field Devices may be stored in the Modbus 40,xxx registers in the Status RTU, if desired, allowing a host system to manage communication statuses for all the field units in one place. See the section Communication Status Registers 196653 for more information on field unit status values.
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| Attributes | Function |
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| Object Type | Clients |
| Parent(s) | System |
| Instance | Must be 0 |
Master Channels Placeholder
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| Attributes | Function |
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| Object Type | Master Channels |
| Parent(s) | System → Clients |
| Instance | Must be 0 |
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Database Flush (DumpRTDB_V2)
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| Properties | Values |
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| Interval Delay | Scans between RBE data refreshes. If RBE Flag parater is set to "All DBM Flags", there is one interval delay per flag (interval x 4 for each flag). |
| RBE Flag | Which RBE Flags in DBM to set |
| Device List | Select which field units to enable RBE flags. If empty, update ALL RTDB's |
HART Commands
The HART Commands object provides HART command options for Field Unit HART 196653 objects' poll tables.
See the Protocol_HART-Master protocol documentation for information on configuring HART Commands.
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See the Protocol_HART-Master protocol documentation for information on configuring HART Commands.
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