Echelon ISI - Manual (Page 75)

73 ISI Programmer’s Guide
Neuron ID to be tracked must be discovered and written to the addressTracking
variable when a connection invitation is accepted. When sending an
(acknowledged) network variable message, this message is explicitly constructed
like an application message, with explicit addressing provided using address
details from the addressTracking variable.
Turnaround Connections
You can create a turnaround connection on an ISI device. A turnaround
connection is a connection between two network variables on the same device.
The following limitations apply for ISI turnaround connections:
• The connection host for the turnaround connection must be the device
containing the connected network variables.
• Only one local assembly can enroll with the host assembly, but
assemblies on other devices may also be enrolled.
• The host assembly must contain at least one output network variable.
• Applications overriding the IsiGetNextNvIndex() function to apply
multiple network variables to a shared selector may only support ISI
turnaround connections if these multiple network variables are all output
network variables.
• ISI turnaround connections can only be created with manual or controlled
enrollment. You cannot create turnaround connections with automatic
enrollment.
An alternative to creating a turnaround connection is to create an application-
level connection. This is a connection where your application passes the data
written to an output network variable to the function or when task that reads an
input network variable. An application-level connection is easy to implement and
requires fewer network resources such as connection table space or NV selectors.
The primary disadvantage of an application-level connection is that it is invisible
to any network management tools that may later be used to transition an ISI
network to a managed network.
To create a manual turnaround connection, select one host assembly on a device,
and then add at most one member assembly per device and enrollment. If this
member assembly is on the hosting device, a turnaround connection will be
created.
Customizing the ISI Connection Table
You can customize the ISI connection table . The connection table is a table
containing the state and details of all connections that the device has joined.
The ISI engine maintains this table and uses the information in this table to host
or join connections. By default, the ISI implementation provides a small
connection table with eight entries suitable for devices with limited resources.