Integration of Field Devices in a PROFIBUS Environment
H. Kleines, R. Madlener, K. Zwoll
Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany
Abstract
Forschungszentrum Jülich (FZJ) introduced PROFIBUS
to slow control systems in the context of physics
experiments by developing a first generation ofPROFIBUS controllers. These controllers are based on amicrocontroller and just implement layers 1 and 2.
Because of their limited performance and functionality,
FZJ developed a new family of PROFIBUS controllers, inco-operation with an industrial company. The new
PROFIBUS interfaces are based on the modern family ofSiemens VLSI protocol chips. The whole range of protocol
options without PA has been implemented. For simple,
cost efficient adaptation of sensors and actuators a single
chip solution has been chosen.
The paper will discuss the benefits of the diverse
PROFIBUS options with respect to possible applications
also in the field of experiment control. Central design
decisions regarding hardware and software architecture
will be discussed and a report of the experiences as well as
first performance measurements will give an impression of
the overall effort and possible problems.
1 Introduction
PROFIBUS, being a national German (DIN 19245 part I- IV) and an international European (EN 50170 Volume 2)
standard, has become the most widely accepted fieldbus
technology in Europe with more than 1000000 installed
nodes [1]. A major reason for its success is the scalability
in technology and functionality based on a common core.
It is functionally scaleable by supporting dedicated,optimised protocol versions (DP, FDL, FMS, PA) andtechnologically scaleable by supporting designs based on avariety of protocol chips with different functionality downto pure software designs based on the integrated UARTs ofmicrocontrollers.
Forschungszentrum Jülich (FZJ) takes the role of a user
as well as a developer of PROFIBUS components.
Developments have been undertaken always together withindustrial companies. Therefore each described
implementation can be used in industrial applications aswell as in FZJ for experiment automation and control.
Because of the complexity of the PROFIBUS
architecture, the selection of the appropriate PROFIBUS
option for a given application scenario is a main issue.
Also the variety of implementation options demands a
careful analysis of the requirements.
2 The PROFIBUS protocol family and its implementation options
According to Fig. 1 PROFIBUS is defined as a collapsed
architecture supporting layers 1,2 and 7 of the ISO
reference model. For the optimised support of dedicatedapplication areas, the three versions FMS (Fieldbus
Message Specification, DIN 19245 part II), DP (Decentral
Periphery, DIN 19245, part III) and PA (ProcessAutomation, DIN 19245 part IV) have been defined arounda common core, the Fieldbus Data Link (FDL, DIN 19245
part I).
FMS Application

ProfilesLayer 7

DP Application

PA Application

ProfilesProfilesFieldbus Message
Specification (FMS)
Lower Layer Interface (LLI)

DP Extensions (DPE)

Decentral Periphery (DP)Layers3-6

empty

Layer 2

Fieldbus Data Link (FDL)

Layer 1

RS-485 or Fibre Optic

FMSDP

IEC 1158-2

PAFig. 1: The PROFIBUS protocol family[1]
PROFIBUS FMS is a universal communication
protocol, primarily directed at the cell level for thecommunication between intelligent automation devices(e.g. PLCs). The FMS application layer is based on anobject oriented client server model derived from the ISO
MMS standard, which already incorporates automation
functions [2]. Until now, the FMS protocol is rarely used
due to its complexity and reduced performance comparedto DP or FDL. But in larger process control applications it
offers consistent semantics also down to the field level,thus simplifying design and configuration.
PROFIBUS DP has been designed for the optimised
connection of simple, low cost I/O in a time criticalenvironment. Typically, one master accesses the fixed I/Ospace of slaves in a cyclic way. So a DP system can beviewed as a distributed PLC. Most of the installed
PROFIBUS equipment in industry follows the DP
protocol, because it specifically fulfils the need forinterfacing simple front end equipment [3].
The newest version PROFIBUS PA has incorporated
results from the Interoperable Systems Project (ISP) and isspecifically designed for process control applications in a
explosion-hazardous environment [4].
FDL specifies a token bus protocol between masters
with optional slaves. The direct access to FDL (without
FMS or DP) often has been used in the early PROFIBUS
applications but now it is being replaced continuously byDP.
Three transmission technologies are supported:• RS 485 with baudrates up to 12 MBit/s,•

intrinsically safe physical layer according to IEC 11582 (H1 bus with 31.25 kBit/s)• Fibre optic transmission
Several dedicated profiles have been defined in thecontext of FMS, DP and PA. A profile specifies thecommunication behaviour of dedicated device classes (e.g.
PLCs, linear encoders, sensors, multiturn actuators), thus
reducing the implementation effort and simplifying theexchange of devices from different vendors.
PROFIBUS is defined as an asynchronous protocol.
Thus it was possible to implement a first generation of
PROFIBUS interfaces based on microcontrollers inparallel with the development of the DIN standard. Theseimplementations are purely done in software using theintegrated UARTs without having to rely on any dedicatedprotocol chip. Today, there is a wide range of ASICs
available (e.g. from IAM, Motorola, Siemens, DELTA t,Smar), allowing dedicated designs where high performanceor offloading of the CPU are required. Complete slave
designs purely in hardware are possible.
Because of performance, functionality and long term
support the following Siemens devices - supportingbaudrates up to 12 Mbit/s - seem to be most interesting.

Fig. 2: Typical application field of the selected PROFIBUS
VLSI controllers [5]•ASPC2: protocol chip implementing the complete
MAC layer of PROFIBUS. It supports theimplementation of FMS master, FMS slave and DPmaster. Because of the missing baudrate detection theDP slave functionality is not supported.
• SPM2: single chip solution for simple DP slaves
without CPU. It implements the complete DP slavefunctionality and contains a parallel interface (64 bitI/O) for directly accessing peripheral components.
• SPC4: protocol chip implementing the slavefunctionality of PROFIBUS layer 2 and parts of DP. It
supports the implementation of FMS slaves and DPslaves. It can directly be interfaced with SIM1, a VLSI
chip for the intrinsically safe physical layer according
to IEC 1158-2, thus supporting PROFIBUS PA.
Fig.2 illustrates a typical application scenario incorporating all three ASICs in industrial control applications.
Together these ASICs support all possible protocol
options of PROFIBUS. So they have been selected as thebase of a new family of PROFIBUS controllers developedby FZJ.
The variety of hardware options is complemented by theavailability of several portable protocol stacks for theindividual ASICs and microcontrollers. Additionally, there
is a variety of support tools (network analyser, configurator, etc.) available.
3 Requirements for a new family of PROFIBUS controllers
Forschungszentrum Jülich (FZJ) has implemented afamily of first generation PROFIBUS controllers based ona microcontroller (NEC V25+) in order to introduce
PROFIBUS in slow control systems for physics
experiments and industrial applications [7]. Because of
their limited functionality (just layer 1 and 2) andperformance these interfaces are considered to be out ofdate. A modern design should make use of protocol chips
and implement also the upper layers.
In order to avoid a major investment in a new family ofinterfaces, the core technology was implemented in cooperation with the industrial company Babcock Prozeβautomation GmbH (BPA).
BPA manufactures a process control system as well as ascaleable family of multiturn actuators (BabcockMatic I,
typically used for the adjustment of valves, based on a 420mA interface in combination with digital I/Os) and isexperiencing a strong market pressure to provide
PROFIBUS interfaces for their actuators as well as fortheir process control system.
So the basic design decisions for the PROFIBUS controller of the actuator had also to take the following requirements of BPA's process control system into account:• support of FMS and of DP,• PROFIBUS master functionality,• PROFIBUS slave functionality for low cost designs.
• high performance,• the CPU of intelligent controllers should be compatible to Motorola 68K CPUs, because they are used in
the automation layer of the process control system.
• redundancy [6]Besides redundancy all defined options are required by
PROFIBUS applications inside FZJ, including slow
control of experiments as well as remote monitoring andcontrol of embedded CPU systems and power supplies like
CAMAC, FASTBUS and VMEbus. In the context of slow
control systems the new family of PROFIBUS controllers
connects our specific equipment to the open world ofindustrial modular board systems (e.g. SMP), PLCs,sensors and actuators [7].
4 Design of the new family of PROFIBUS devices
4.1 FMS/DP-master interface
The requirements listed in the previous sections demand

the implementation of a DP/FMS master based on apowerful microcontroller and protocol chip for the MAClayer. Here the Siemens ASPC2 was selected because ofperformance and support. The existence of a portable
PROFIBUS protocol stack and the 68K-compatibility leadto the microcontroller MC68340.
In order to use the PROFIBUS controller in variety ofapplications and configurations and due to space
limitations, it was designed as a modular system of two
directly connected boards. One board contains the basecontroller with CPU logic and PROFIBUS part, the otherone is a peripheral board containing components like
ADCs, DACs and binary I/Os, which do the interfacing tothe actuator. An additional peripheral board for PCI bus
has been developed on the base of the AMCC S5933 PCI
Controller and a Dual Port RAM (8K*16) for the transferof messages between host and controller.

I/Os for interfacing the actuator (Fig. 4). PROFIBUS partand peripheral devices could be integrated on one board.
Of course, there was no software development effort on thePROFIBUS interface, at the cost of a little bit higher
software complexity in the master. So this approach isconsiderably cheaper than the FMS/DP master.

Fig. 4: Block diagram of the simple DP slave [8]In order to have some intelligence in the front end (e.g.
for statistics or calibration), also an intelligent DP slave
based on the SPC4 was implemented. By using a similar
design as for the ASPC2 based board, basically byreplacing the ASPC2 with the SPC4, a maximum synergy
regarding hard- and software development could beachieved.
5 Performance measurements

Fig. 3: Block diagram of the PROFIBUScontroller (core and peripheral board)
As usual, the base controller is implemented as anintelligent subsystem according to Fig. 3, with a central
address/data/controlbus
connecting
theCPU
MC68340FE16, 256 KBytes FlashEPROM, 256 KBytes ofstatic RAM and the ASPC2. For the simultaneous supportof FMS and DP the FlashEPROM has to be increased to512 KBytes. The control logic contains reset logic, a watch
dog timer and the redundancy support [6]. The CPU is a
microcontroller containing all required peripheral
components like interrupt controller, timers and UARTs
and has a programmable clock rate which has been tested
up to 16 MHz, the value used here. A dedicated medium
attachment unit supports a redundant cabling system.
The portable protocol software was acquired from theGerman company Softing and adapted to the new hardware. The application software, which maps PROFIBUS
services to interactions with the actuator, was implemented
as a task under control of the board level operating systemkernel SOS (Softing Operating System). SOS wasdelivered by Softing as an execution environment for themodules of the protocol stack, thus offering a standardisedinterface for accessing the services of FMS, FM7, DP andSOS.
4.2 Implementation of the DP slave interfaces
In order to achieve a cost-efficient design, a DP slave
version for the actuator interface without CPU wasdeveloped. It is based on the SPM2 with some glue logic
for accessing the "ident number" and the PROFIBUS
address of the station as well as the analogue and digital

In [9] extensive measurements of FDL and FMS havebeen presented based on the standard user method andhardware monitoring. The measurements concentrated onthe overall performance characteristics exhibited to theuser application and Fig. 5 summarises the results together
with new measurements of DP.
At the individual layers the minimum response times forthe following acknowledged services have been measured:• DP: data_exchange service (based on FDL serviceSRD)• FMS: read service (based on FDL service SDA)
• FDL: SDA service (Send Data withAcknowledgement)
Fig. 5 shows that the use of protocol chips leads to amajor decrease of response time (Factor of 5 between oldand new design at FDL layer). This is mainly due to thefact, that the responses of at DP and FDL are generated
completely in hardware. So we measured that the "reaction
time" of the chips (e.g. Time between incoming andoutgoing token, incoming SDA request and outgoing SDA
acknowledgement, etc.) is basically identical with thesetting of the timer min_tsdr (minimum station delayresponder). Minimal settings of min_tsdr are 11 bit times
for the SPM2 and 17 bit times for the ASPC2, thus
depending on the baudrate (e.g. 22µs and 34 µs at 500
kBit/s). Because the reaction times of stations, especiallythe token transfer time are a crucial issue for each token
passing protocol, the main advantage of the use of thechips is the dramatic increase of overall bandwidth on thebus. This gets especially evident when considering, that thereaction time of a pure microcontroller based
implementation is in the order of 0,5 ms with a maximum

baudrate of 500 kBit/s (instead of 12 MBit/s). The effect of
the baudrate on response time is determined by thephysical transmission time on the medium. So it can becomputed directly and is neglectable for small message
sizes. Because of the inherently low degree ofparallelisation, this holds also for the throughput between
two stations, as shown in [9].

Fig 5. Minimum Response Time t in various PROFIBUS
configurations measured at 500 kBit/s
So the overall response times are basically determined bysoftware delays. This gets especially evident when looking
at FMS. Here we measured, that the response time isalmost proportional to the CPU clock.

Fig. 7: Poll Cycle duration measured at 6 MBit/s
DP exhibits its strength when one master accesses
several SPM2 based slaves in a cyclic mode. In this mode,the data exchange does not occur on explicit request of theapplication, but asynchronously to/from a dual ported
memory, leading to a major speed up. Fig. 7 shows cycle
duration (including read and write operation at each slave)measured for 1,2,...,6 slaves at 6 MBit/s and extrapolated
to 16 slaves.
6 Conclusions
The PROFIBUS architecture provides a variety ofoptions for dedicated application areas. So, a carefulanalysis of the communication requirements of an
application is a key issue for the implementation of a anapplication based on PROFIBUS. This leads to an
appropriate selection of options as well as available
hardware and software components, thus optimising costs,
maintenance effort, performance and integration effort.
The developments of FZJ represent optimised designs for
all protocol options of PROFIBUS, apart from PA. Forinterfacing simple slave devices the SPM2 solution shouldbe the preferable solution. Otherwise, additional firmware
has to be integrated in the devices, leading to more
complex systems.
Measurements showed, that the increase of the overallbandwidth in a PROFIBUS system is a main advantage ofmodern PROFIBUS ASICs. In addition to this, extremely
short response times can be achieved when accessing
SPM2-based DP slaves in a cyclic mode. Because of thehardware support for DP, it can be assumed that also SPC3and SPC4 provide similar response times. But thisassumption must be proven by future research.
References[1] http://www.profibus.com[2] S.W. Zhang: "Fieldbus technology overview and its
impact on industrial automation", FieldComms USA,Boston, June 1997
[3] M. Deppe : "Anforderungen an ein modernes
Feldbussystem - Was bietet PROFIBUS DP", iNet 95,
Karlsruhe, Juni 1995
[4] A. Schimanski: "Profibus PA Field Instrumentation",
FieldComms UK, November 1996
[5] "PROFIBUS Technische Druckschrift", PROFIBUS
Nutzerorganisation e.V, Oktober 1995
[6] H. Kleines, R. Madlener, J. Holzer, K. Zwoll:"Implementation of a redundant PROFIBUS-Interface
for an industrial Actuator", FieldComms Europe,
October 1996
[7] K. Zwoll, H.-J. Eisenbach, J.L. Sarkadi: "Open
Fieldbus Communication (PROFIBUS) in Physics
Experiments", Real Time Data '94, Dubna, Russia,June 1994
[8] D. Becker: "Entwicklung einer Anschaltung an ein
Feldbussystem auf der Basis von PROFIBUS-DP",
Diplomarbeit FH Aachen, 1996
[9] H. Kleines, R. Madlener, J. Holzer, K. Zwoll: "Auniversal Family of PROFIBUS Interfaces for Process
Control Applications", Fieldcomms USA, Boston,June 1997