Self-configuring modular electronic system

In an electronic system, an arithmetic device is provided between successive bus terminals or between successive modules, respectively, with an identification signal applied to a bus input that is routed from one bus terminal to the next bus terminal until the identification signal has passed through all bus terminals in order to identify the modules. The identification signal is subjected to an arithmetic operation and consequently changed in each arithmetic device before it is forwarded to the next bus terminal, wherein the &#8220;results of the operations&#8221; are used for identifying the individual bus terminals and the individual modules, respectively.

BACKGROUND OF THE INVENTION

The invention relates generally to self-configuring modular electronic systems and, particularly, to a computer system having a data and address bus with multiple lines and having several addressable modules electrically connected to the bus via respective module lines.

An electronic system of this type is known from EP 0 491 480 A2. In order to address electronic modules in computers, a series of bus line pairs between successive slots are interchanged in accordance with a binary pattern such that each slot has an unmistakable coding. During an initialization phase of the computer, a bit pattern of predetermined signals is applied to the bus line pairs. Due to the reversal of the bus line pairs, each slot then receives a different bit pattern such that each station is able to identify its assigned slot and thus receives an unmistakable address.

U.S. Pat. No. 4,727,475 describes a self-configuring modular computer system with a central processing unit and several modules that are connected to a bus. A call signal generated by the central processing unit is received by the module located closest to the central processing unit. This module applies an identification signal to the bus, with the central processing unit generating a base address for the module. This process is repeated until all modules have been assigned a bus base address. This system requires that each module have an individual identifier at the beginning of the address assignment process such that all modules can be individually addressed sequentially.

DE 33 47 357 A1 describes a similar device for assigning addresses to plug-in modules. In this case, a characterizing module identifier is applied to each module. In addition, each module is given a slot identifier. During initialization, all modules are called by means of the slot identifier and give the control unit their respective module identifiers. The control unit then assigns the modules their relevant address by addressing the slot identifier with the relevant address being used for the additional exchange of data.

DE 29 32 868 A1 describes a data processing circuit arrangement with a central processing unit to which several peripheral devices are connected. Each peripheral unit has an electronically programmable address memory, with each address memory being connected to a central processing unit via a separate enabling line that is only assigned to the respective address memory. Each individual peripheral unit can be addressed and assigned an address by the central processing unit via this enabling line.

DE 39 38 018 C2 describes an information processing system and a method for determining its configuration. Each slot for modules has separate connections, the potential levels of which process a slot-ID-signal in order to allow the individual addressing of the respective slot. A certain address can then be assigned to each module at the corresponding slot by a central processing unit.

DE 44 21 344 A1 describes a supplementary card for a computer which has a predetermined digital hardware identification. This identification makes it possible to address each individual supplementary card and assign an address for a bus system to each card by a central processing unit.

The entire disclosures of the aforementioned references are incorporated herein by reference.

In known systems, the configuration and the identification of the connected modules is realized by means of reversed bus lines, by assigning different initialization addresses to the individual modules, or by providing additional lines that are assigned to the respective modules. For this reason, a self-configuring modular electronic system that has a simple design and that makes it possible to connect a series of addressable modules to a common bus, where all modules may also be absolutely identical, is desired.

SUMMARY OF THE INVENTION

The present invention meets the above needs and overcomes the deficiencies of the prior art by providing a self-configuring modular electronic system that has a simple design and that makes it possible to connect a series of addressable modules to a common bus, where all modules may also be absolutely identical.

The invention is based on the idea of routing an identification signal from module to module, and to change this identification signal in defined fashion during the routing. So that, each module receives a different identification signal that unmistakably differentiates it from the remaining modules and, for example, may be used for addressing purposes.

The identification signal is changed with the aid of arithmetic devices that, for example, may consist of full adders and respectively add a signal that corresponds to a number (e.g., a 1 ) to the identification signal. The result of the addition is routed to the next bus terminal or the next module such that a separate address, e.g., an address that is incremental by 1 (address number), can be assigned to each module.

In this case, the arithmetic devices may be directly arranged on the bus between respectively adjacent slots and/or integrated into the individual modules.

The invention can be used for configuring or addressing individual components of a computer system, e.g., individual microprocessors, network cards, memory cards, etc., which are connected to the corresponding bus terminals. However, it is explicitly noted that the invention may also be used in any given electronic system in which several modules to be identified are connected to one another via a line system.

Devices for electrically connecting the modules to the data and address bus, e.g., sockets or terminal strips, are preferably provided on the individual bus terminals.

The spatial arrangement of the individual modules may be selected differently. According to one variant, the modules are arranged adjacent to one another in a single plane on a printed-circuit board. Alternatively, it is also possible to stack several modules one atop the other, with the individual modules being interconnected and to the bus via electronic connecting means, e.g., sockets. Such a three-dimensional arrangement of the individual modules makes it possible to achieve a high component density and thus contributes to the additional miniaturization of the system. In addition, it is possible to arrange several such stacks consisting of individual modules adjacent to one another.

The individual modules may consist of independent central processing units, independent computers, peripheral devices, memory modules or the like, all of which communicate with one another via a common system. The individual modules may also have their own intelligence. However, this is not absolutely imperative. In particular, it is possible to use several absolutely identical modules.

Alternatively, the invention may comprise various other methods and systems.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The computer system according to FIG. 1 contains a bus system with n 1 bus lines L 0 -Ln that represent the conventional address and data lines of a bus B. Bus terminals BA 0 -BAr that, for example, are formed by slots or solder contacts are provided on the bus B. The modules M 0 -Mr are connected to these bus terminals, with each module M 0 -Mr containing module lines B 0 -Bn that are respectively connected to an assigned bus line L 0 -Ln. In addition, each adder ADD 1 -ADDr is respectively provided between each bus terminal BA 0 -BAr and between each module M 0 -Mr, with said adders being electrically connected to the bus lines L 0 -L 3 .

Pull-down resistors Pa 0 -Pd 3 that are connected between ground and an assigned bus line L 0 , L 1 , L 2 and L 3 , respectively, are provided at a bus input BE in.

In order to identify the bus terminals of the individual modules M 0 -Mr which, for example, takes place when switching on the electronic system the bus lines L 0 -L 3 are connected to ground potential, which corresponds to a signal with the value 0 via the pull-down resistors Pd 0 -Pd 3 . This signal with the value 0 is fed to the module M 0 via the module lines B 0 -B 3 that are connected to the bus lines L 0 -L 3 , with this module determining from this signal that it is connected to the bus B at the bus terminal BA 0 .

The signal with the value 0 is simultaneously fed to the adder ADD 1 that adds the value 1 to the signal. The resulting signal with the value 1 is fed to the next module M 1 and the adder ADD 2 via the module lines B 0 -B 3 . Similarly to the module M 0 , the module M 1 determines from this signal that it is connected to the bus terminal BA 1 .

The adder ADD 2 also adds the value 1 to the signal with the value 1 it receives, with said adder routing the resulting signal with the value 2 to the adder ADD 3 and the module M 2 that identifies its assigned bus terminal BA 2 . The identification of the bus terminals of the remaining modules takes place similarly.

After the identification of the bus terminals of the individual modules M 0 -Mr has taken place, the bus lines L 0 -L 3 can be used as normal lines.

Alternatively, the respective bus terminal number can also be assigned to the modules by a subsequent adder, i.e., the number 1 is assigned to the first module by the adder ADD 1 , the number 2 is assigned to the second module by the adder ADD 2 , etc.

Arithmetic devices other than the adders ADD 1 -ADDr shown, e.g., multipliers, may be alternatively provided. However, it must be ensured that the resulting signals obtained by the respective operation can be clearly differentiated such that the bus terminals can be identified.

FIG. 2 shows an embodiment in which the adders ADD 1 -ADDr are integrated into the modulesh M 0 -Mr. In order to identify the bus terminals BA 0 -BAr, a signal with the value 0 is fed to the adder ADD 1 of the module M 0 via the module lines B 0 -B 3 . The adder ADD 1 adds a value 1 to this signal and routes the resulting signal to the adder ADD 1 of the next module M 1 via the module lines B 0 -B 3 and the bus lines L 0 -L 3 connected to these module lines, respectively. The signal is processed similarly by the next adder. The modules M 0 -Mr then determine their respective bus terminal BA 0 -BAr either from the signals fed to the modules via the module lines B 0 -B 3 or from the signals obtained from the additions which are routed to the next module via the module lines B 0 -B 3 .

If one of the bus terminals is unoccupied, i.e., if, for example, no module is connected to the bus terminal BA 2 , it must be ensured with corresponding devices that the bus lines L 0 -L 3 are electrically connected to assigned bus lines L 0 -L 3 such that the modules Mr- 1 and Mr are able to determine their bus terminal. This may, for example, be achieved with resistors R 0 -R 3 as described below with reference to FIG. 3 .

In FIG. 3 , the module Mr is connected to the bus terminal BAr, and the bus terminal BAr 1 is unoccupied. In contrast to the embodiment shown in FIG. 2 , the bus lines L 0 -L 3 are respectively connected to the assigned bus lines L 0 -L 3 via a resistor R 0 -R 3 in FIG. 3 . The resistors R 0 -R 3 may be 1 resistors for example. If a module is not connected to a bus terminal, the resistors R 0 -R 3 route the output signals of the previous bus terminal that are applied to the bus lines L 0 -L 3 or the output signals of the previous module to the bus lines L 0 -L 3 and thus to the next bus terminal or the next module, respectively. If a module Mr is connected as is the case with the bus terminal BAr, the signals routed via the resistors R 0 -R 3 are overwritten by the signals conveyed via the module lines B 0 -B 3 or B 0 -B 3 since the signals routed via the module Mr have a lower resistance than the signals conveyed via the resistors R 0 -R 3 .

It is also possible to use bus terminals instead of the resistors R 0 -R 3 as described below with reference to FIGS. 4 a and 4 b.

FIG. 4 a shows a bus terminal 1 with a housing 2 and two elastic, electrically conductive clamping springs 3 and 4 that contact one another and that are connected to bus line L 0 and L 0 respectively. This means that the clamping springs bypass the bus terminal if it is unoccupied.

FIG. 4 b shows the bus terminal 1 of an occupied bus terminal, with a connector 5 of the module M 1 ( FIG. 2 ) being plugged into this terminal. The connector 5 contains the module lines B 0 and B 0 that are connected to the adder ADD 1 and that are respectively electrically connected to the bus lines L 0 and L 0 via the clamping springs 3 and 4 .

There exist several options for the spatial arrangement of the individual modules M 0 -Mr. For example, the modules may be arranged adjacent to one another in a single plane as indicated in FIGS. 1 and 2 . Alternatively, it is also possible to realize a three-dimensional arrangement of the individual modules.

FIG. 5 shows an embodiment in which several modules M 1 -M 6 are stacked one atop the other. Electric contacts K 1 -K 9 that are connected to the individual bus lines (not shown) are provided on a base printed-circuit board P. The contacts K 1 -K 9 may, for example, be formed by a terminal strip (or by a socket according to DE 297 08 461 U1, the entire disclosure of which is incorporated herein by reference) that is arranged on a main printed-circuit board of the computer. The module M 1 contains corresponding opposing contacts GK 1 -GK 9 that are electrically connected to the contacts K 1 -K 9 of the printed-circuit board. Contacts K 1 -K 9 are provided on the side of the module M 1 which is located opposite to the counter contacts GK 1 -GK 9 , with said contacts being designed in accordance with the contacts K 1 -K 9 of the base printed-circuit board P. This allows the stacked arrangement of the individual modules shown.

Similar to the embodiment shown in FIG. 2 , adders ADD 1 -ADD 6 are integrated into the individual modules M 1 -M 6 , with each adder also adding a 1 as indicated by the addition terms 1 2, 1 3, etc. The wiring of the modules M 1 -M 6 and the adders ADD 1 -ADD 6 may be realized similarly to FIG. 2 .

The three-dimensional arrangement of the modules M 1 -M 6 shown in FIG. 5 saves much space, so that an additional miniaturization of electronic systems is possible. Naturally, it is also possible to arrange several stacks on a base printed-circuit board as shown in the basic circuit diagram according to FIG. 6 .

FIG. 6 shows a basic circuit diagram for the stacking of modules, with this figure containing the schematic stacks ST 1 , ST 2 and ST 3 that respectively consist of no more than n modules (in this case, n 4). The stack ST 1 is fully occupied and thus contains four modules M 0 -M 3 , the stack ST 2 consist of the modules M 4 -M 6 , and the stack ST 3 consists of only one module M 8 . However, the stacks ST 2 and ST 3 may also contain a total of four models as the case with the stack ST 1 . This is indicated by the modules M 7 , M 9 , M 10 and M 11 that are indicated by broken lines.

In order to identify the respective bus terminals of the individual modules, adders ADD 0 -ADD 3 , ADD 5 -ADD 8 and ADD 9 -ADD 12 , respectively, are provided similarly to FIG. 2 . These adders are integrated into the individual modules. During the identification of the bus terminals, a signal with the value 0 is applied to the bus lines L 0 -L 3 , with the modules M 1 -M 4 of the stack 1 determining their respective bus terminals BA 0 -BA 3 in accordance with the embodiment shown in FIG. 2 .

The signal with the value 0 is simultaneously fed to an adder ADD 4 that is arranged directly on the bus B between the two stacks ST 1 and ST 2 and adds a value n ( 4 ) to this signal. The thus obtained signal with the value 4 is fed to the first module M 4 of the stack ST 2 , with this module determining the assigned bus terminal BA 4 , and with the adder ADD 5 adding a 1 and forwarding a signal with the value 5 to the module M 5 . In the same way, the modules M 5 and M 6 respectively determine their assigned bus terminals BA 5 and BA 6 , respectively.

The signal with the value n ( 4 ) generated by the adder ADD 4 is also fed to an adder ADD 8 . This adder also adds a value n ( 4 ) and feeds the resulting signal with the value 2n ( 8 ) to the module M 8 of the stack ST 3 , with this module determining its bus terminal BA 8 from this signal.

The number added to a signal value by the adders ADD 4 or ADD 8 corresponds to the maximum number of modules in a stack, i.e., the number n ( 4 ) in this case. If it is desired to use stacks consisting of more than 4 modules, the adders ADD 4 and ADD 8 must to add correspondingly higher numbers. Thus, it is ensured that each module is able to determine its individual bus terminal such that it can be individually addressed if the stacks ST 1 -ST 3 are fully occupied.

Preferably, the bus B has exactly n select bus lines provided for identification purposes. If more than 2 n modules M 0 -M 18 to be identified are connected to the bus B, the identification signal is successively fed to the first 2 n modules M 0 -M 15 at a first reset signal level (Reset 1). In the embodiments shown in FIGS. 1-6 , only four bus lines, the bus lines L 0 -L 3 , were used. This means that no more than 2 4 16 modules can be identified.

If more than 16 modules are to be identified, additional bus lines can be provided or the identification can be performed in two stages as described below with reference to FIGS. 7 a and 7 b.

In the embodiment shown in FIGS. 7 a and 7 b , additional modules can be identified with the four bus lines L 0 -L 3 and a reset line that is provided already in conventional computer systems, i.e., it is possible to obtain one additional bit without requiring an additional bus line.

Analogous to the previously described embodiment, an adder ADD 0 -ADD 18 is assigned to each of the modules M 0 -M 18 respectively. In this case, each adder is integrated into the corresponding module M 0 -M 18 . In addition, each module contains two plugs DOWN and UP, wherein an UP plug is connected to a corresponding DOWN plug of the subsequent module, and the DOWN plug of the module M 0 is connected to the bus lines L 0 -Ln.

During a first identification phase, in which Reset 1 as shown in FIG. 7 a , i.e., in which the reset line is active, the digital signal 0000 which corresponds to the decimal number 0 is fed to the module M 0 via the lines L 0 -L 3 . Subsequently, the signal is forwarded to the next module, with the adders ADD 0 -ADD 14 each adding a 1 such that, for example, the digital signal 1110 which corresponds to the number 14 is fed to the module M 14 and the digital signal 1111 which corresponds to the number 15 is fed to the module M 15 .

The adders ADD 16 -ADD 18 of the next modules M 16 -M 18 either add a 1 or a 0 depending on the reset signal. In the first identification phase, in which Reset 1, the adders A 16 -A 18 add a 0, i.e., the signal 1111 of the module M 15 is initially forwarded to the next modules M 16 -M 18 unchanged ( FIG. 7 a ).

When the reset changes from 1 to 0, i.e., when the reset changes from active to inactive ( FIG. 7 b ), the modules M 0 -M 14 store their input digital values in four lower slot bits S 0 -S 3 , i.e., the module M 0 stores 0000, M 1 stores 0001, etc., and M 14 stores 1110. In addition, the modules M 0 -M 14 store a 0 in a fifth bit S 4 . The next modules M 15 -M 18 , in contrast, store a 1 in the fifth bit S 4 .

In a second identification phase, in which Reset 0, i.e., in which the reset is inactive, the modules M 15 -M 18 , which have stored a 1 in the fifth bit, are determined. Subsequently, the assigned adders ADD 15 -ADD 18 also add a 1. Since only four lines L 0 -L 3 used for identification are provided in this embodiment, an overflow that is not taken into account at first occurs at the adder ADD 15 . Consequently, the adder ADD 15 delivers the signal 0000 to the module M 16 , whose adder ADD 16 generates the signal 0001 and delivers this signal to M 17 , whose adder ADD 17 generates the signal 0010, etc. Subsequently, the modules M 15 -M 18 , whose fifth slot bit is 1, also store the signals they receive via the bus lines L 0 -L 3 in the lower bits S 0 -S 3 .

This means that an unmistakable identification of all modules M 0 -M 18 is possible despite the overflow occurring at the adder ADD 15 , due to the values 0 and 1 stored in the fifth slot bit S 4 and the values stored in the lower four slot bits S 0 -S 3 .

In this embodiment, the bus lines L 0 -L 3 cannot be used as normal data lines after the completion of the identification phase. However, their use as data lines possible if an additional bus line (not shown) is provided which, for example, indicates the end of the configuration.

If such an additional bus line is provided, each of the four lines L 0 -L 3 can be separately configured as an input or output on the DOWN and the UP side. In addition, a signal can be passed from one side to the other or vice versa. It is even possible for one of the modules M 0 -M 18 to switch both sides (DOWN and UP) as outputs and deliver two signals or to switch both sides as inputs and receive two signals.

FIG. 8 a shows a variation in which two base printed-circuit boards P 1 and P 2 are provided. Several modules are plugged onto these printed-circuit boards. This variation is referred to as the base printed-circuit board variation below. Two stacks ST 0 and ST 1 are plugged onto the base printed-circuit board P 1 , and one stack ST 2 is plugged onto the base printed-circuit board P 2 . The stack ST 0 consists of only one module M 00 , while the stacks ST 1 and ST 2 , respectively, are formed by several modules M 11 , M 12 , and M 13 and M 22 and M 23 , respectively. These modules are stacked one on top of the other similar to a tower. Each of the modules shown in FIG. 8 a contains a lower plug UST with contacts K 1 -K 10 that are plugged onto complimentary counter contacts GK 1 -GK 10 analogous to the embodiment according to FIG. 5 . In this case, the modules M 00 and M 11 are plugged directly onto the counter contacts GK 1 -GK 10 of the base printed-circuit board P 1 , and the module M 22 is plugged directly onto the counter contacts GK 1 -GK 10 of the printed-circuit board P 2 .

The modules of the stacks ST 1 and ST 2 , respectively, contain an upper plug OST that is provided with counter contacts GK 1 -GK 10 corresponding to the base printed-circuit boards P 1 and P 2 respectively.

In addition, each module contains a first storage unit SN and a second storage unit EN, where the value stored in the storage unit SN indicates the stack number of the respective module, and the value stored in the storage unit EN indicates the tier number. The stack number and the tier number together form the slot numbers of the modules. The module M 00 belongs, for example, to the stack 0 and is arranged in its lowest tier, which is also numbered 0 in this case. This results in the slot number 00. However, the lowest tiers of the stacks ST 1 and ST 2 are numbered 1 and 2 , respectively. This results in the respective slot numbers M 11 and M 22 , respectively. This numbering is discussed in greater detail below.

The modules of the stacks ST 1 and ST 2 , respectively, contain an adder analogous to FIG. 5 . During an identification phase, these adders each add a 1 to a signal to be routed to the next higher module via the contacts K 1 -K 4 . The module M 00 does not require an adder or an upper plug because here it forms the only module of the stack ST 1 .

Naturally, the upper plugs OST and the adders ADD 13 and ADD 23 , respectively, may also be omitted from the top modules M 13 and M 23 of the stacks ST 1 and ST 2 , respectively. All modules may also be absolutely identical to the modules of the stacks ST 1 and ST 2 .

The modules M 00 , M 11 and M 22 are each connected to the bus lines L 0 -L 9 and to a reset line of the bus B via the contacts K 1 -K 10 , the counter contacts GK 1 -GK 10 and the module lines B 0 -B 10 . Analogous to FIG. 1 , an adder ADD 1 and ADD 2 is provided in between the individual bus terminals BA 0 , BA 1 and BA 2 , respectively, where these adders add a 1 to a signal applied to the bus lines L 0 -L 3 .

The module identification for the base printed-circuit board variation is described below.

In a first identification phase, in which the reset line is in the state 0, the individual modules identify their respective stack number, even if only one module is provided like with stack ST 0 . For this purpose, when the system is turned on a signal with the value 0 is applied, for example, to the lines L 0 -L 3 , said signal is fed to the module M 00 , and said signal corresponds to the stack number SN of this module. The adder ADD 1 adds a 1 to this signal and routes the resulting signal with the value 1 to the lowest module M 11 of the stack ST 1 via the module lines B 0 -B 3 . This module routes the received signal unchanged to the next higher modules M 12 and M 13 of its stack ST 1 . The adder ADD 2 simultaneously adds a 1 to this signal and routes the resulting signal with the value 2 to the modules M 22 and M 23 , respectively, of the stack ST 2 .

In the base printed-circuit board variation, a different stack number SN is fed to each stack ST 0 -ST 2 , where said stack number is routed to all modules of the stack via the contacts K 1 -K 4 and the counter contacts GK 1 -GK 4 , respectively.

When the reset changes from 0 to 1, each module stores its respective stack number with the rising edge of the reset signal.

In a second identification phase, reset 1. This corresponds to the normal operating condition of the electronic system. In this phase, the individual modules determine their respective tier numbers EN. For this purpose, a signal that, for example, has the value 0 is applied to the bus lines L 0 - 03 and fed to the module M 00 and to the modules M 11 and M 22 , respectively, via the corresponding adders ADD 1 and ADD 2 . The lowest modules M 11 and M 22 of the stacks ST 1 and ST 2 , are assigned the respective tier numbers 1 and 2, respectively.

The adders ADD 11 -ADD 13 and ADD 22 -ADD 23 each add a 1 to these tier numbers and route, or transmit, the resulting value to the next higher module of the respective stack. For example, the tier number 2 is assigned to the second module M 12 of the stack ST 1 by the adder ADD 11 .

According to this method for example, in the base printed-circuit board variation the lowest module of a stack with the stack number 14 would be assigned the tier number 14 , and the next higher module of the stack 14 would be assigned the tier number 15 . The adder of this module would then also add a 1 which in instances in which only four module lines B 0 -B 3 are used for identification purposes lead to an overflow, i.e., to an addition 15 1 0. Thus, module in the third tier of the stack 14 would be assigned the tier number 0 , the fourth module would be assigned the tier number 1 , etc. An unambiguous identification of the modules of a stack is possible if an overflow occurs only if each tier number occurs once within the stack.

If the numbering of each of the lowest modules should begin with 0, a subtractor can be provided for each stack, where the subtractor subtracts the respective stack number from the tier numbers.

FIG. 8 b shows a variation of the invention in which all modules are stacked one on top of the other in only one stack. This variation of the invention is referred to as the stack variation below. The individual modules M 00 -M 03 correspond to the modules of the stacks ST 1 and ST 2 , respectively, shown in FIG. 8 a . In contrast to this figure, the contacts K 1 -K 4 of the lower plug UST of each module M 00 -M 03 are additionally connected to one respective pull-down resistor Pd 1 -Pd 4 . The contacts K 1 -K 4 and the pull-down-resistors Pd 1 -Pd 4 are connected to assigned counter contacts GK 1 -GK 4 via the adders ADD 00 -ADD 03 . The remaining module lines B 5 -B 10 are looped through the individual modules M 00 -M 03 , i.e., their signals are routed unchanged from one module to be next higher module. Analogous to FIG. 8 a , the module line B 10 is connected to a reset line. Additional bus or module lines may be provided, but this aspect will not be discussed in greater detail. The lowest module M 00 does not necessarily have to be plugged into a base printed-circuit board, but-as shown here it can be connected to the bus B via a bus connection plug BST or in.

As an alternative to the embodiment shown in this figure, the bus B may also terminate at the lowest module M 00 , i.e., it can also connect the modules M 00 -M 03 to one another only within the stack.

The identification of the individual modules is described below.

After the system is turned on, the only stack number SN in the stack variation is determined in a first identification phase, in which Reset 0. In this case, no signal is initially transmitted to the bus lines L 0 -L 3 such that the lowest module M 00 receives a signal with the value 0 which is generated by its pull-down resistors Pd 1 -Pd 4 and corresponds to the stack number. While Reset 0, a signal can be routed from the lower plug UST to the upper plug OST of a module without performing an addition directly or unchanged. In this case, all modules M 00 -M 03 receive the same stack number 0.

When the reset changes from 0 to 1, the stack number 0 is analogous to the base printed-circuit board variation stored at the rising edge of the reset signal, where the tier numbers of the individual modules are determined while Reset 1. For this purpose, a signal, to which each adder ADD 00 -ADD 03 of the individual modules M 00 -M 03 adds a 1 and then stores the resulting tier numbers, is supplied via the bus lines L 0 -L 3 and the module lines B 0 -B 3 , respectively. Alternatively, the tier number of the lowest module can also be impressed by the assigned pull-down resistors Pd 1 -Pd 4 .

In conclusion, it should be noted that the determination of a stack number in the stack variation is actually unnecessary because only one stack is provided. However, in certain applications it is desirable to use the same module for the stack variation as well as for the previously described base printed-circuit board variation. This is the reason why the assignment of a stack number is also provided in this case.