wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

55-2 Industrial Communication Systems
capturing and hiding platform-dependent functions of devices. Each FB has a set of input and output
variables. The input variables are read by the internal algorithm when it is executed, while the results
from the algorithm are written to the outputs.
The use of FBs makes the control device openly programmable and easily reconfigurable. IEC
61499-compliant devices can easily interface each another, thus providing for seamless distribution of
different tasks across different devices. Users may create their own program using standard FB types.
Thus, the IEC 61499 architecture enables encapsulation, portability, interoperability, and configurability.
Portability means that software tools and hardware devices can accept and correctly interpret software
components and system configurations produced by other software tools. With interoperability,
hardware devices can operate together to perform the cooperative functions specified by one or more
distributed applications. With configurability, devices and their software components can be configured
(selected, assigned locations, interconnected, and parameterized) by multiple software tools.
Being an architecture for distributed systems, IEC 61499 needs to address the issue of communication
between distributed devices. It needs to be mentioned that particular networking mechanisms,
such as protocols and middleware, are beyond the standard’s scope. Interfaces to particular
networking mechanisms can be implemented in IEC 61499 by communication interface function
blocks (CIFBs).
There is a small but growing toolset for FB design. The Function Block Development Kit (FBDK) [2]
remains the most widely used, because it is the oldest and is free for educational use. The new version
of the ISaGRAF industrial control design software with support for IEC 61499 FBs is described in [3,4].
The nxtControl tool [5] is another example of a professionally developed design environment that can
generate code for a range of BECKHOFF and WAGO control devices. A number of developments at
academic and research organizations can be represented by CORFU [6] and the open-source projects
4DIAC IDE [7] and FBench [8,9].
In order for FBs to become executable on a variety of hardware, hardware vendors must provide support
for the standard. The options remain limited, but are on the increase. There are currently several options
for executing FBs. First, any platform that can execute standard Java byte code can run the FBRT that is a
part of FBDK. This includes desktop computers running any major operating system. Embedded execution
option includes the Elsist Netmaster II, which runs a cut-down version of Java standard edition (J2SE).
Tait Control Systems MO’Intelligence units run Java micro edition (J2ME) and are supplied with a port of
the FB run-time and vendor-supplied service interface FBs for hardware access. These units are available
in several formats with support for DeviceNet and an integrated motor drive option.
The 4DIAC consortium has developed an open-source run-time for FB execution FORTE [10]. It has
been ported to a variety of hardware platforms and was chosen by nxtControl as a primary run-time
target. FB compiler based on synchronous semantics is reported in [11]. Other academic developments
include Java-based FUBER run-time [12], real-time Java [13], and Linux [14]-based run-times, as well as
the Java-based run-time implementing the cyclic execution model [15].
This chapter provides an introduction to IEC 61499 and especially to its communication-related features
by discussing an example of a simple distributed control system. For a more fundamental introduction
to IEC 61499, the reader is referred to [16,17] and for implementation ideas to [18].
The chapter is structured as follows. First, the example is introduced. Then implementation of its control
in terms of IEC 61499 FB application is presented and discussed. This allows to see the simulation
capability of IEC 61499 as well. Next, the two-stage design concept of IEC 61499 is presented followed
by a detailed description of abstract communication models of IEC 61499. Then the example is extended
functionally. Also, the hardware architecture is changed to a distributed one, where the connectivity is
provided by two different types of networks. Explicit communication FBs are added to the application.
The underlying mechanisms for implementation of those FBs using services of Modbus and control
and information protocol (CIP) protocols are described in detail. These are followed by a discussion on
the impact of communication semantics on the distributed application behavior and failure models for
distributed applications. The chapter is concluded with a summary and a list of references.
© 2011 by Taylor and Francis Group, LLC