Rockwell Automation 1788-CN2FF ControlNet-to-FOUNDATION Fieldbus H1 Linking Device User Manual - Manual (Page 6)

1788-6.5.1 - January 1999
1-2 Introduction
The linking device is similar to an I/O subsystem. An I/O subsystem
typically contains several I/O modules. Each module has a number of
channels. The channels perform one of these functions:
• analog input (AI)
• analog output (AO)
• discrete input (DI)
• discrete output (DO)
The linking device models the I/O modules in software. The linking device
has four types of custom function blocks:
• multiple AI block
• multiple AO block
• multiple DI block
• multiple DO block
Each of these function blocks has multiple channels. These function blocks
are similar to the I/O modules in the I/O subsystem. Each channel of these
custom blocks is associated with an analog/discrete input or output value in
a Fieldbus device. You establish the association when you configure the
system.
The linking device creates a ControlNet object (analog input, analog output,
discrete input, or discrete output) for every channel that is associated with a
Fieldbus device. In summary the linking device makes the function blocks
in Fieldbus devices visible as ControlNet objects on the ControlNet.
ControlNet devices and controllers can access the Fieldbus devices as
though they are ControlNet devices.
The function blocks in Fieldbus devices have contained parameters and I/O
parameters. Contained parameters are mainly used to configure the function
blocks. I/O parameters are used in distributed control of the process. These
parameters are made visible as attributes of the ControlNet objects. The
linking device publishes and subscribes to the I/O parameters on the
Fieldbus network, and consumes and produces the corresponding
ControlNet object attributes on the ControlNet as assembly objects. The
linking device can be Link Active Scheduler (LAS) on all of the connected
Fieldbus networks.
Configuration and Monitoring
The linking device permits the NI-FBUS Fieldbus Configurator on a PC
connected to ControlNet to configure Fieldbus devices as if the configurator
were directly connected to the Fieldbus network. Fieldbus devices have a
physical address, a physical device tag, and function block tags. They also
have schedules for function block execution, information on connections
between function blocks, and so on. All of these are configurable.