Patent
1995-07-20
1997-11-25
Sheikh, Ayaz R.
395299, G06F 1300
Patent
active
056921330
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to an arrangement having several card slots into which a number of functional units can be plugged, with the card slots interconnected by a system bus having data and control lines and by address lines.
The present invention may be advantageously applied, for example, in a programmable controller consisting of central controllers and expansion units. Such a device is disclosed in Siemens catalog "SIMATIC S5, ST 54.1" (1992). The programmable controller has a number of card slots for receiving components, such as central processing units (CPUs) which execute control programs, and digital or analog input/output components for inputting and outputting digital or analog signals. Several CPUs are customarily used in devices of this type to handle complex control tasks, thus requiring a so-called "coordinator" or "arbiter" to regulate the manner in which the CPUs access a system bus connecting the various components. In the disclosed device, however, the coordinator must be plugged into a particular card slot provided especially for that purpose.
In programmable controllers of the type just discussed, it is known to have a central bus node manage bus accesses by a plurality of other bus nodes. For example, B. Wiemann, Bus Systems--Parallel and Serial Bus Systems in Theory and Practice, 43-58 (1984) discloses that within a bus system, a central bus node may be connected to another bus node by two lines. The central bus node functions as an arbiter, receiving bus requests from the other bus node over one connecting line and informing the other bus node of a bus grant decision over the other connecting line. The central bus node may coordinate bus accesses by a plurality of bus nodes in this manner.
The requirement of a dedicated card slot for these known approaches to bus access management is undesirable in that it limits flexibility in system configuration. Accordingly, an object of the present invention is to provide an arrangement for a device, such as a programmable controller, in which a central bus node responsible for running a bus can be plugged into any card slot.
SUMMARY OF THE INVENTION
An arrangement for managing bus access in a device, such as a programmable controller, according to the present invention includes several card slots interconnected by both a system bus having data and control lines, and by address lines. Bus request lines, bus grant lines and bus lock lines are run to connectors of the card slots. The arrangement further includes a means for generating a card slot code for each card slot.
This arrangement further includes a number of plug-in functional units, of which at least two are suited to executing read and/or write accesses to other units over the system bus. In each case, these plug-in functional units include a means for connecting the bus request, bus grant and bus lock lines to the functional units; an arbiter for running the system bus; a means for determining the card slot code of the card slots into which functional units suited to executing read and/or write accesses are plugged; a means for generating a position code from these card slot codes; and a means for activating the arbiter in case the position code corresponds to a specific selection code.
Advantageously, no special component is required to run the system bus since each functional unit capable of executing read and/or write accesses (e.g., a CPU component) is provided with its own arbiter. Only one of the arbiters will be active during system operation, while the rest remain passive. The arbiter to be activated is determined during start-up of the device; for example, during an initialization phase after a supply voltage is switched on.
The arrangement according to the invention is particularly well-suited for application in a programmable controller; and preferably in a programmable controller having a central controller and at least one expansion unit which are interconnected via a connecting cable containing the system bus and address lines. Features and
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Abert Michael
Block Siegfried
Bozenhardt Johannes
Leigsnering Franz
Pfatteicher Werner
Sheikh Ayaz R.
Siemens Aktiengesellschaft
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