Echelon ISI - Manual (Page 11)

9 ISI Programmer’s Guide
during development for capturing and interpreting ISI messages. The ISI Packet
Monitor application is described in Developing and Debugging the ISI
Implementation in Chapter 4. A few of the key ISI messages are introduced in
this section. All of the ISI messages are described and documented in the ISI
Protocol Specification . Following are a few of the most important ISI messages:
• Device Resource Usage Message (DRUM) —this message is periodically
broadcast by all ISI devices. It includes the physical address (Neuron
ID), logical address (domain, subnet, node IDs), non unique ID, and
channel type for the device. The extended version of this message adds a
device class and usage field for use in device tracking. You can enable
the extended version by passing isiFlagExtended into IsiStart*() (see
Starting and Stopping Self-Installation in Chapter 2).
• Connection Status Messages (CSMs) —this group of messages is used to
create, maintain, and delete connections. There are multiple types of
connection status messages, including messages to manually create a
new connection (CSMO), automatically create a new connection (CSMA
and CSMR), and delete a connection (CSMD). The CSMO, CSMA, and
CSMR messages include the group ID, primary functional profile,
primary network variable type and direction, variant number, and
number of network variables for an offered connection. Devices that
receive these messages can use the information—plus optional user
interaction—to determine whether or not to join the connection. The
extended version adds fields to determine if the connection is
acknowledged or polled, the scope of the connection and parts of the
program id, and the primary network variable member. You can enable
the extended version by passing isiFlagExtended into IsiStart*() (see
Starting and Stopping Self-Installation in Chapter 2).
• Timing Guidance Message (TIMG) —this message is periodically
broadcast by all domain address servers. It includes information about
network size and latency. It is an optional message, but if available, ISI
devices use this information to schedule all periodic message based on
network size. This ensures efficient use of the channel bandwidth and
minimizes the overhead of the ISI protocol
ISI Limits
This section describes ISI limits. Some of the limits depend on options selected
by your device application, and some depend on which ISI library you choose to
link with your application. The ISI libraries and features of each are described in
Optimizing the Footprint of ISI Applications . Those who use your devices will
need to know the resulting limits for your devices. Guidelines for documenting
these limits will be available at
www.echelon.com/isi .
Device Count Limits
ISI networks support up to 32 devices for ISI-S networks and up to 200 devices
for ISI-DA networks. ISI networks will not immediately stop functioning if these
limits are exceeded. Increasing the number of devices over the supported limits