Electrical computers and digital data processing systems: input/ – Input/output data processing – Input/output addressing
Reexamination Certificate
2002-01-17
2004-06-22
Gaffin, Jeffrey (Department: 2182)
Electrical computers and digital data processing systems: input/
Input/output data processing
Input/output addressing
C710S003000, C710S009000, C709S251000, C709S253000, C711S204000, C711S213000, C370S255000, C370S257000, C370S258000, C370S909000
Reexamination Certificate
active
06754721
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for configuring a station connected to a field bus, wherein a logical address is allocated to said station, and in particular to a method of allocating a logical address to such a station.
The invention further relates to a station suited for being connected to a field bus and having means for receiving and evaluating a bus telegram, said station further having a memory for storing a logical address which is to be allocated to said station.
A field bus is a communication system especially used in industrial automation technology for connecting spatially distributed sensors and actuators to higher-order controls and computers. It is a characteristic feature of such a field bus that the different units connected to the field bus are connected one with the other via a collective bus line which allows, at least in principle, any units to communicate one with the other via the field bus, without being individually connected by cables. The units connected to the field bus will be generally referred to as stations hereafter.
With field buses data transmission as such takes place based on fixed rules, known as protocols. With respect to such protocols, two basic kinds of field buses can be distinguished, namely field buses with a so-called message-oriented transmission method on the one hand, and field buses with a so-called I/O-oriented transmission method on the other hand. In case of the first-mentioned transmission method each station is allocated a unique address. For transmitting data from one station to another, the transmitting station adds the address of the receiving station to the data telegram comprising the message to be transmitted, as prescribed by the selected protocol. Being supplemented by that address, the data telegram is then dispatched via the bus line, and the receiving station can recognize from the address allocated to it that the message is intended for it. It is a matter of course that each station must necessarily know the address allocated to it with such message-oriented transmission methods. Usually, the address is assigned to the stations by means of coding switches which must be present in each station, and on which the address assigned to the respective station is preset. The field bus known as CAN bus may be taken as an example of a field bus working with a message-oriented transmission method.
In contrast, an I/O-oriented transmission method does not require allocation of a unique address to each of the different stations, at least not in principle. Rather, communication between stations is effected under control of a higher-order station, known as bus master. The bus master is the only authority capable of initiating data traffic. The bus master has exact knowledge of the structure of the bus, especially the sequence and order of the stations connected to the bus. The bus master transmits an exactly specified data frame that contains as many data fields as stations are connected to the field bus. The data fields of the data frame are circulated from one station to the next and finally back to the bus master. Once the bus master receives the start word of the data frame initiated by itself, i.e. the data frame has been fully circulated through the entire ring structure of stations, it generates a signal that causes all stations to take over the message present at the respective station at the moment of that signal. Consequently, distribution of data to be transmitted to the different stations is established here based on the bus structure known to the bus master, the latter “fills” the data fields of the data frame in an appropriate way. The field bus known as Interbus may serve as a preferred example of a field bus using such a transmission method.
A detailed description of the Interbus is found, for example, in the German book entitled “Interbus—Grundlagen und Praxis (Fundamentals and Practice)” by Baginski et al., published by Hüthig-Verlag, 1998. As a special advantage of the Interbus, this book underlines that no unique addresses are required for data transmission. This also means that there is no need to equip the different stations with coding switches or the like.
For safety-critical processes, such as monitoring of emergency tripping devices, no field bus systems have been used heretofore, since the ideally desired 100% failsafety could not be guaranteed due to their freely accessible structure. It was only recently that it was tried to use field bus systems also in safety-critical applications by means of additional failsafety measures such as additional protocols intended to guarantee failsafety. As part of these safety protocols, addresses are to be assigned also in case of the Interbus, at least to those stations that are involved in safety-critical processes. Said addresses then allow such stations to check if a message received is actually intended for themselves. Errors may occur, for example, if changes are made in the order or the type of the stations actively connected to the Interbus and if the bus master does not get knowledge of such changes quickly enough. This may happen erroneously when a station is exchanged, for example.
For implementing a failsafe Interbus it is therefore a requirement that addresses be allocated to the failsafe stations in a failsafe way. This has been achieved heretofore by providing the stations with a coding switch which is preset in a suitable way to allocate the unique address to the station. Such kind of address will be described hereafter as logical address, because it may be independent of the physical structure of the field bus, and especially of the sequence of the connected stations.
However, use of coding switches for allocating logical addresses causes certain disadvantages. One of such lies in the fact that any coding switch requires mechanically adjustable elements in some form or the other. Mechanical components, however, are comparatively costly in terms of production so that their mass production is expensive compared with purely electronic components. In addition, mechanical components are always subject to wear which prevents to employ simple components, especially in the case of safety-critical applications. A further disadvantage connected with the use of coding switches can be seen in the fact that such switches must always be located near the particular station. For complex process controls in industrial applications, however, the different stations connected to the field bus may be remote one from the other by up to several hundred meters. When coding switches are used, the logical addresses must be allocated in this case at the very location of the station so that in some cases long distances must be overcome that make the setting and configuration laborious and complicated. Finally, such decentralized configuration measures always involve the risk that track may be lost, which may result in erroneous allocations of addresses, especially when a defective station is exchanged.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of the before-mentioned kind by means of which a station can be allocated a logical address in a failsafe manner and without any mechanically operable coding switches being required. In addition, it is an object of the present invention to provide a station of the before-mentioned kind that can be configured using such a method.
This object is achieved by a method as mentioned at the outset, said method comprising the steps of
transmitting the logical address from an address-allocation unit to the station;
transmitting a physical address from the address-allocation unit to said station, said physical address corresponding to an assumed physical position of said station relative to the field bus;
verifying said physical address that has been transmitted to said station based on an actual physical position of said station relative to the field bus; and
storing said transmitted logical address in a memory of said station depending on the verification of sa
Cohen & Pontani, Lieberman & Pavane
Gaffin Jeffrey
Patel Niketa
Pilz GmbH & Co.
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