8300 | 8315 L&J Tankway Software Description |
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4.4Gathering Point Data
For Host to TankGate communications, there are two primary methods for gathering point data. These methods are listed below:
4.4.1Standard Request-Response Format
The Host issues scan requests, and the TankGate responds with the data.
The Scan method has the advantage of being deterministic, the response time to a particular request will always be the same.
This method has the limitation that if there are many points defined in the TankGate, it often takes several requests to obtain all of the data. Most of the time data has not changed since the last request, so this results in inefficiencies in update times. This situation is often the case in systems where there are many digital points that do not change frequently.
4.4.2Change of State Format
The Host issues scan requests based on a Change of State condition. Some systems refer to this as Event Mode. The TankGate keeps track of the items that have changed since the last Host request. The Host can issue a single request of ‘tell me what has changed since my last request.’ The TankGate will respond with the results, which include addressing information about the data. In a typical system, this results in a significant improvement in the throughput rate for data.
When FuelsManager is the Host system, the Change of State method has the advantage of being very efficient. Only the data that has changed is reported. Change of State is not available when using Modbus.
4.4.3Change of State-Related Parameters
In order to support the Change of State method, many points have additional configuration parameters included.
Parameter | Description |
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Value | One of the parameters which will be returned to a Change of State request by |
| the Host. Most Software Blocks are designed so that the Value parameter is |
| the main parameter of interest. |
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Report | Is used for Change of State processing only |
| Causes automatic notification to the Host (in response to a Change of State |
| Request) when the Value Changes State. |
| Valid values are High, Low or No. Report=No disables notification. |
| Points with Report = High have higher priority than points with Report = |
| Low. |
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Maxtime | Is used for Change of State processing only |
| Specifies the maximum time (in secs) between automatic Change of State |
| data being sent to the Host in response to a Change of State Request. |
| When the Maxtime period expires, the Value to is forced appear as if it has |
| changed even if is has not, ensuring that data is sent to the host periodically. |
| Setting Maxtime to 0 disables this option. The maximum is 255 seconds. |
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