Varec 8300 series, Installation And Operation Manual, Page: 34 / 150

Software Description Tank Gate Interface
24 Installation and Operations Manual
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.
4.3.3 Change of State-Related Parameters
In order to support the Change of State method, many points have additional configuration
parameters included.
Note Not all Host protocols support the Change of State method. The RTU Slave protocol
used with FuelsManager supports either method.
Note The Modbus protocol is Scan-based. Therefore, the Report and Maxtime parameters
have no meaning.
4.3.4 Modbus Communications
Some versions of the Tank Gate Interface are capable of communicating with Modbus
compatible devices with both Modbus Masters and Slave devices. The Tank Gate Interface is
flexible, allowing communications with devices that strictly comply with the Modicon Modbus
protocol, as well as devices with more advanced Modbus implementations such as Honeywell’s
APM-SIO.
The Modbus Slave protocol handler responds to read and write requests from a Modbus master
system. A detailed description of the Modbus Slave protocol handlers follows.
Modbus Slave
The Modbus Slave protocol handler is enabled by setting the Protocol parameter of a COM point
to Modbus Slave. COM 0 of the Tank Gate Interface is auto sensing. If a Modbus Master requests
data from the Tank Gate Interface, the Tank Gate Interface will automatically detect that Modbus
is being used and invoke the Modbus Slave protocol handler. The Modbus Slave protocol handler
responds to requests from Modbus masters. A MODGW point is automatically created to provide
Parameter Description
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.
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.
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.
Deadband
LevelDeadband
TempDeadban
d
Affects the Change of State processing. It allows users to filter out insignificant
changes, freeing the communications link to send other data.