Rockwell Automation 1788-CN2FF ControlNet to Foundation Fieldbus H1 Linking Device Installation Instructions - Manual (Page 21)

ControlNet-to-Foundation Fieldbus H1 Linking Device 21
Publication 1788-IN051D-EN-P - February 2004
1788-CN2FF and Foundation Fieldbus Devices
Devices do not equate to connections. The current recommended number of devices per H1
port is 8 and the maximum number of devices per 1788-CN2FF module is 16 for any type of
bus power used.
These numbers are for Non-IS (Intrinsically Safe) class devices only. IS device maximums are
even lower, depending on all the configuration constraints of a particular application.
Understanding the 1788-CN2FF Connection and Device Relationship
One connection does not equal one device. The maximum recommended number of devices
per each H1 port is 8 for a total 16. That maximum takes into account that you have an
optimal sized network, the correct number of connections, followed wiring guidelines and
you don’t have 16 devices that exceed the current limitation of your systems’ power supply.
Many devices require 2 connections (e.g. an AO) and some devices that can require 3 or more
connections (e.g. a PID). The number of connections needs be considered when counting
devices. You may have 8 devices that exceed the connection limits of the module. For
example: AIs take one connection, AOs will require two, and PIDs will need at least 2 but
could use more depending on how it is wired.
The maximum number of connections (30) is specified as a combination for BOTH channels.
In addition, you need to account for other process aspects such as loop time and stale limits
for your network segments. You need to take into account the length of your cables and spurs,
the number of devices per spur, power consumption of each device, etc.
ATTENTION
The maximum number of “connections” is 30 per CN2FF. The
recommended number of “devices” is 8 per H1 port on the
CN2FF. If you exceed the maximum number of connections or
the recommended number of devices, system performance could
be compromised.
ATTENTION
Be sure to follow the wiring and installation requirements in the
Foundation Fieldbus publications listed in the section Additional
Information on page 3.