CA1240064A

CA1240064A - Modular battery powered business systems

Info

Publication number: CA1240064A
Application number: CA000496232A
Authority: CA
Inventors: Flavio Manduley
Original assignee: Pitney Bowes Inc
Current assignee: Pitney Bowes Inc
Priority date: 1984-12-20
Filing date: 1985-11-26
Publication date: 1988-08-02
Also published as: EP0186881A2; US4649491A; JPS61151724A; EP0186881A3; DE3583225D1; EP0186881B1

Abstract

MODULAR BATTERY POWERED BUSINESS SYSTEMS
ABSTRACT OF THE DISCLOSURE
A computation and control module suitable for use in a variety of postal scales as well as other types of mailroom equipment is disclosed. The module includes a microprocessor and associated circuitry, connectors for connecting ROM, which store firmware for controlling the microprocessor, and PROM, which store postal rate charts; an input/output connector; a serial interface for communications with postage meters; a non-volatile memory for storing parameters specific to particular units; and an auxiliary input/output connector.
The auxiliary input/output connector is driven by selected, memory mapped interface circuitry mounted on the PROM card.
The module also includes a load cell interface and a power supply. In one embodiment switches, responsive to the microprocessor, are provided for sequentially energizing various connectors and interfaces, so as to reduce power requirements, Systems comprising a plurality of computation and control modules are disclosed. Other systems including battery powered modules mechanically and electrically interconnected by a power distribution bus are also disclosed, as a modular power bus.

Description

BACKGROUND OF THE INVENTION

Postal scale are well known in the art; simple sprin~
scales with scale char~s ~hich map a weight range into one or more postal rates having existed for decades. More recently, with ~he increased availability of solid state micro-processors, load cells and low-cost analog-to-digital (A/D~
converters it has become feasible to provid~ electronic, digital postal scales with greatly increased capabilities.
Still more recently, the availability of low power components such as CMOS logic and memories, and liquid crystal displays has significantly reduced the power requirements of digital devices while the development of new battery technology, such as nickle-cadmium batteries, have increased the energy density of batteries. One result has been the development of powerful portable devices such as "laptop" computers. Beyond simple portability however the inventor of the present inven~ion has recognized that business systems, particularly mailroom equipment, can be formed using battery powered modules which could be interconnected to form various systems so that as additional modules are added to increase capabilities the total power available to the systern is also increased; freeing the user of the need to concern himself with power supply requirements as the system is expanded.
Thus, it is an object of the subject invention to provide business systems, and more particularly mailroom systems, which are modular and expandable without concern for power supply requirements.

; , ~;:~

, ~

More particularly, it is an object of the subject invention to provide such systems wherein both power and mechanical interconnections between modules are made in a single, simple step.
Other objects and advantages will be apparent to those skilled in the art from consideration of the detailed description set forth below and of the at~ached drawings.

- 2 -RIEF SUMMARY 0~' ~HE INVENTION
The above objects are achieved and the disadvantages of theprior art are overcome in accordance with the subject inven-tion by mean~ of a digital sy~-tem comprising a pluralit~ of modular subsystems with at leas-t one subsystem including a battery for supplying power to the system. Connectors provide signal interconnections between the ~ubsy~tems and each ~ubsystem is mechanically and electrically connec-ted to a common, substantially rigid~ extended power distribution bus eo that power from each of ~aid batteries is shared by each of said subsystem~ and said 3ubsystems are mechanically interconnected to form a single unit. ~he bus further comprises a plurality of modular sections eaoh seotion compri~ing; a pair of extended conduotorc Por providing poeitive and negative bu~es; a rigld, in~ulating ~lelnent .el.x0d to e~ch of the conduotor~ for holding the conductor~ in a spaced parallel relationship; means for providing mechanical and electrical connection between the conductors and the sub~ystems; and a pair of connecting means one at each end of each section for mechanically and electrically connecting each section to adjacent similar sections to form the power di~tribution bu~.
In a second embodiment of the ~ubject invention the power distr:ibution bus comprises a number of modular seotion~ each further comprising a pair of extended conductor3 which serve a~ positive and negative bu~es, a rigid, in~ulating elemen-t fi~ed to each of the conductor~ and holding the conductors~ in a ~paced, parallel relationship, mechanical and electrical connec-tors between the :
Pg/

3 --, :~, ' ' .:

conductor~ and each subsystem and a pair of connector~, one at sach end of each section for substantially rigidly mechanically and electrically connecting sections to form a power distribution bus.
~ hu~, the ~ubJect invention advantageou31y provides a modular, ba-ttery powered business system, which may preferably be a mailing system, ans which i~ readily expandable without concern for overburdening of power supplie~.

- 3a -., :, . . .

~¢~
~RIEF D SCRIPTION OF THE DR~WINGS
Figure 1 shows a schematic block di.agram of a computation and control module for use in postal scales and other mailroom equipment.
Figure 2 shows a schematic block diagram of a mailroom system.
Figure 3 shows a schematic block diagram of a computation and control module substantially similar to that shown in Figure 1, which further shows power switching axrangements used to reduce power requirements.
Figure 4 shows a schematic block diagram of a modular, battery powered mailroom systemO
Figure 5 shows a plan view of a power bus module.

; - 4 - .

DETAILED DESCRIPTION OF PREFERRED
~BOVIMF,NTS OF THE INVENTION

Figure 1 shows a computation and control module for use in postage scales and other mailroom equipment, such as electronic accounting systems, in accordance with the subject invention. A large printed circuit board 10, commonly known as a "motherboard" supports the various components and connectors-comprising the subject computation and control module. An integrated circuit microprocessor and its assoeiated support eircuitry are mounted on motherboard 10 to provide intelligence ti.e., programmable, general purpose computation and control capabilities) for the subjeet module.
Such mieroprocessors are well know to those skilled in the art. l'ypical of such mieroprocessors is the well known Intel Model 8085, manufactured by the Intel Corp., Santa Clara, CA.
Descriptions of the architectural structure of the 8085 and procedures for operationally connecting such microprocessors with various memory and input/output devices may he found in MCS-80/85 Family User's Manual, published by Intel Corp., 1979. Similar mieroproeessors and information are available from other manufaeturers and are well known to those skilled in the art. Aecordingly detailed description of the mieroprocessor, its assoeiated eireuitry and its interfaee to other components is unnecessary to an understanding of the subjeet invention and will not be discussed further.
Conneetors 40, 50, 60 are eonnected to mieroprocessor 20 to allow the easy connection of memory modules to .
d~ 5 : .

~ ~C~

microprocessor 20 ( the term "connector" as used herein is meant to include both single connec~ors or groups oE
connectors used together to perform a function. Similarly, paddle boards and other sub modules may comprise single units or groups of related units.) Connector 40 allows 8K to 24K
bytes of read-only-memoxy (ROM) mounted on paddleboard 42 to be connected to microprocessor 20. This memory is used to store the firmware used to control the postal scale (or other item of postal equipment) comprising the subject module.
Connector 50 allows 8K to 16K bytes of programmable-read-only-memory (PROM) mounted on paddleboard 52 to be connected to microprocessor 20. This memory is used to store postal rate charts and zip-to-zone in~ormation, which information is used to convert zip codes to postal 20nes Eor computin~ postage~
~PROM's are preferred for storing postal rate data since such data is subject to fairly frequent change. However, those skilled in the art will recognize that, once programmed, PROM's and ROM's are functionally the same. Thus, hereinafter, while recognizing ~hat either PROM's or ROMgs may ~e used, I'PROM's'' will refer to postal rate and zip-to-zone memory while ''ROM'SU will refer to firmware memory).
Collnector 60 allows 8K to 16K of additional memory ~ROM or PROM) to be connected to microprocessor 20 to provide an expansion capability for larger systems.
Connector 70 is provided to allow microprocessor 2~ to communicate with a keyboard an-d display (not shown ) to provide an operator interface. Connector 70 provides, as outputs, a serial data line, a serial clock line, 3 lines o~

.
-- S ~

encoded keyboald strobe signals, and a reset signal for clearing the display, all appropriately bufered; a~d 6 lines of keyboard return and an interrupt line as inputs. A +S
volt line and return are provided to supply power to the keyboard and display control logic. This arrangement allows up to 48 keys to be scanned by microprocessor 20 using a conventional strobe and return techniqu~. The keys,used will be defined- (i.e., their meanings mapped) by information stored in PROM's 52 so that definitions of keys may be easily changed and an expanded keyboard may be used with the extended postal rate charts and zip-to-zone information used in more sophisticated models of postal scales.
(Alternatively the keyboard may be defined by information stored in f;rmware ROM's 42).
In other mailroom equipment, such as electronic accounting syskems, a more elaborate and extensive keyboard may be required. Such a keyboard and display would include a keyboard/display controller ~such as the Model8279 manufactured by the above identified Intel Corp~ To allow for this expansion of keyboard capability the data line may be made bi-directional to communicate with the keyboard/display controller.
Preferably the display may be a conventional multi-element flourescent display. High vol~age and filament power may be supplied for the display either through connector 70 or locally at the display.
Remote display connector 80 parallels the display connections of connector 70; providing a data line, data .

~2~

clock and a +5 volt supply and return to allow for the provision o a remote display. The remote display would include its own controller and high voltage and filament supplies~
Connector 9o is provided to allow connection of the postal scale to a postage meter through a secure communications link. Since the operation of a postage meter is equivalent to the purchase of postage it is critical that the transmission of postage information from the postal scale to the meter be error free. A proprietary interface and protocol intended for such error free transmission of postal data to a postage meter is described ln ~.S. Patent Nurnber

4,301,507, for Electronic Postage Meter ~aving Plural Computing Systems to, Soderberg et al, îssued November 17, 1981 and is known by the trade name Echoplex. Connector 90 provides an Echoplex serial data ou~ line and return, a me~er trip line, (which includes special protective circuitry to prevent the generation of false meter trip signals during power on/off transients) and return and a reset line as out-~puts. Inputs provided are an Echoplex serial data-in line, a return, and an interrupt line. A +5 volt line and return are provided to provide a remote reference level for signal detection~ with return. Preferably the +5 volt line is short circuit protected.

-ConnPctor 90also provides a unregulated +5 volt line which may be used to provide power to a two port interface expansion module mounted on a separate board. In more , .

sophisticated scales such a board allows communication with a postage meter and with devices such ~s electronic accounting systems.
It should be noted that the Echoplex circuitry provided in the module of the subject embodimient does not include optoisolators but relies on the isolators of the connected postage meter. However the two port expansion board may preferably include a port with isolators for communication with devices such as electronic accounting systems which may not include isolators.
Connector 100 is provided to allow input/output expansion. A number of undefined lines are connected from firmware connector 40 to connector 100. Th.is allows additional inputtoutput circuitry to be mounted an ROM
paddleboard 42. Thus, for example t a fielcl upgrade of a postal scale to provide a printer output may be achieved simply by changing paddleboard 42; the substitute board would not only include firmware to control the printer but also input~output circuitry which would provide a printer port at connector 100. (Those skilled in the art will recognize that since microprocessors such as the 8085 use "memory mapped I/O"~ where input/output registers are addressed as memory locations, input/output circuitry mounted on paddleboard 42 is directly accessable to microprocessor 20)..
Non-volatile memory 110 comprises a small amount of memory such as electrically-erasable-programmable-read-onlY-memory (E2PRO~s3. This memory is discussed separately from other memory since it is used to store data which is peculiar _ g _ G~l to particular scales. It is used to store information such as load cell calibration constants, (e.g , zero, correction factors) configuration parameters (e.g., meter in use, automatic set mode) and cus~omer location zip code ~for zip-to-zone conversion). Preferably this dal-a will be stored with redundancy so that errors may be detected and, possibly, corrected. It is also preferred that the data be electrically alterable so that it may be changed or corrected through microprocessor 20.
Digital interface and connector 120 is provided to allow transmission of raw digital da~a from the load cell transducers, after con~ersion by the associated analog to-digital converter (~/D). Details of the design of this interface would depend on the particular load cell and associated circuitry chosen ~or the load cell but would be well within the abilities of those skilled in the art.
tNumerous patents including U.S. Patent Numbers 4,139,892 and 4,350,216 show techniques for interfacing loaa cells to microprocessors) Having selected a particular interface design and protocol it would be routine for a person skilled in the art to adapt it to a product family of scales;
essentially requiring only the provision of a sufficien~
nwmber of data bits to allow the desired precision through the whole family of scales~
Preferably the load cell subsystem includes its own control processor. This would allow the load cell raw di~ital data, commonly known as counts, to be transmitted with error de~ection/correction redundancy (check sums, etc~

.

., and two way communications, to check status, request retransmission in the event of an error, etc Further incorporation of a microprocessor into the load cell subsystem would reduce the design of interface 130 to a routine processor to processor communications problem~
In use the function of the module of the subject invention wculd be controlled by the sel~ction of ROM
paddleboard 42, PROM paddleboaxd 52 and the information stored in non-volatile memory 110. For example, if the module of the subject invention were intended for use in a low range, unsophisticated scale with limited keyboard and display capabilities board 4~ would be chosen lacking input/output circuitry and with ROM's programmed with firmware appropria~e for the intended unsophisticated application. Board 62 would be selected with PROM's defining a limited selection of postal rates and defining a limited keyboard. In a very unsophisticated system zip-to-zone iuformacioll mig','c be entered through the keyboard~ In such a system non-volatile memory 110 would only include load cell calibration constants and no zip-to-zone conversion tables would be provided.
In a more sophisticated system boards 42 and 52 would be selected to provide increased capabilities, ~ip-to-~one con~ersion, increased postal rate informationt automatic meter setting, extended keyboard definitions, etc. In such a system non-volatile memory 110 would include calibration constants, configuration parameters and customer location zip code.

., ~2~ 6~L
Programming for postal scales is disclosed in U.S.
Patent No. 4,286,32S, to Dlugos, et al, for System And Method For Co~ Domestic And International Postaqe, issued _ August 25, 1981; and U.S. Patent No. 4,325,440 to Crowley, et alJ for Method And System For Com~uting Special Fees In A
Parcel Postaqe M eterinq System, issued April 20, 1982, Such programming could readily be trans:Lated into firmware for a particular microprocessor by a per-son skilled in the art.-Further the module of the subject invention may alsoreadily be used in mailroom systems such as electronic accoun~ing systems, manifest systems, mailroom management systems or journal printexs. ~These systems are well known for use in mailrooms to record records of postal activity for later retrieval). For example, if the modul~ of the subject ;nvention where intended for use ln a journal printer, board 42 would be selected to include journal printer firmware and printer I/O circuitry connected to expansion connector 100.
Such a system m.ight well require a full, general purpose keyboar~ and display and use the bi-directional serial communications provided through keyboard and display connect~r 70. Data would be received through serial interface 90; and in order to retain data or later retrieval random-access-memory would be provided on paddleboard 62, either through expansion connector 60 and/or by replacing PROM~ on board 52.
Figure 2 shows a ma;lroom system compxising a postal ~cale 200, a conventional electronic postage meter 300 and an ~ 3~3~

electronic system 400. Postal scale 200 comprises module 10-200 in accordance with the subject invention, a load cell subsystem ~10 which provides count data for the item weighed through interface and connector 1~0-200, a port expander 220 connected to Echoplex port 90-200 and a specialized postal scale keyboard and display connected thrc,ugh connector 70-200. Board 42-200 provides firmware which controls module 10-200 in accordance with the desired capabilities. ~n addition to firmware for computing appropriate postage value in accordance with the weight of the item and postal information input through keyboard and display unit 230 board 42-200 also provides firmware for communications with other systems wh.ich may be connected to scale 200. Such communications firmware is selected by the processor (not shown) of module 10 200 in accordanc~ with conEiguration parameters stored in non-volatile memory 110-200. In the system shown module 10-~00 would communicate with a conventional postage meter 300 which may be a meter such as the Model 6500 meter manufac~ured by Pitney Bowes Inc., Stamford, Connecticut, and electronic system 400. In addition to transmitting postage values and trip signals to meter 300 module 10-200 also txansmits postal information such as postage value, weight destination, zip code, etc. to electronic system 400.
Board 52-200 provides appropriate postal rate information and zip to-zone information for scale 200, and also provides information defining the keys of keyboard display unit 230, which is read by a conventional strobe and ; return technique throu~h connector 70-200.

. - 13 -System 4~0 may be any of a number of mailroom systems for logging postal data; such as, electronic accounting systems, journal printers, mailroom management systems, etc.
Such systems also provide for later retrieval of the data either by printerS downloading to a disk, computer interface, or other means.
Such a system is shown in Figure 4 based on module 10-400, which is structurally identical to module 10-200. Board 42-400 provides firmware which defines the data logging and system control functions. Such programming would essentially ir,volve no more than simple data base management and routine ~housekeeping" functions for the system shown and would be well within the skill of those skilled in the art. Boards 52-400 and/or 62-400 would connect RAM memory to module 60-400~
Such R~ storage may be used for temporary storage of logged postal data. (Design of connectors 50 and/or 60 to accept either ROM or R~M memo y would be a outine task well within the capability of those skilled in the art.) As described above scale 200 communicates with system 400 through Echoplex connector 90-200 and expander 220.
System 40 also communicates through Echoplex connector 400 a~d may include expander 420 to allow communication with additional scales.
Device 410, which, as indicated above, may be a printer or other means for retrieving logged data, is connected to module 10-400 through connector 100-400 and appropriate interface circuitry on board 42-400.

:. .

,.

Non-volatile memory 110-400 may contain configuration parameters such the number of scales connected to s~stem 400, the particular model of printer connected, etc.
Because an operator may need to exercise greater control over system 400 it includes a general purpose keyboard and display unit 430 which further includes a control unit 432. Control unit 432 communicates with module 10-400 through the bi-directional data line of connector 70~
400.
Because power supply 30 provides power to all the active components on motherboard 10 as well as other components attached to motherboard 10 it must be sized to support the largest system in which it ma~ be used.
~ccordingly, to avoid burdening less sophisticated systems ~ith the cost of an oversized power supply Figure 3 sho~s an embodiment of the subject invention having a reduced power requirement.
Figure 3 shows a module which is substantially the same functionally as the module shown in Figure 1 (Note that the communications links between subsystems are the same hut are not shown in Figure 3 ~or ease of illustration~.
~ormally open CMOS switches 55, 65 75, 95, llS and 125 are connected in series with the +5 volt lines of connectors 50g 60, 70, 90, non-volatile memory 110 and connector 120, reducing the stand-by power drain on power supply 30. Switch assembly 25 connects the f 5 volt source to an interrupt input of microprocessor 20 and is actuated, either mechanicallyt electro-op~ically, or in some other suitable manner9 by ' g36~

motion of the scale pn (not shown~. In response to the interrupt microprocessor 20 would command power control circuit 130 to close switch 125 to energize the load cell subsyst~n (not shown) and digital load cell interface 120, so that the weight counts from the load cell subassembly can be generated and transmitted. When a stable count input is received switch 125 is opened and switch 115 closed so that the parameters stored in non-volatile memory 110 may be retrie~ed~ Switch 115 is then opened and switch 75 is closed so tha~ the operator may enter the necessary information for the item to be mailed. ~Note that preferabl~ a separate, unswitched ~-5 volt source 72 is also provided to connector 80 to ~eep the keyboard of the keyboard/display unit ~not shown) live so that operation of the scale may also he initiated from the keyboard~ Switch 75 is then opened and switch 50 andO if necessaryt switch 60 are closed to energi~e boards 52 and 62 so that necessary postal rate information and zip-to-zone conversion information may be retrieved. The appropriate postage value for the item to b~ mailed is then determined by microprocessor 20 and switches 55 and 65 are opened. I~ the configuration parameter information retrieved from non-volatile memory shows a postage meter connected switch 9~ is-closed to energize the Echoplex interface and connector 90 for transmission of the postage value information to such meter. Switch 75 is then opened and microprocessor 20 returns to a wait state until the next interrupt ~or command from the keyboard).

.~

Thus~ the peak power demands on supply 30 are substantially reduced, allowing use of a smaller less costly supply. In less sophisticated systems, w:ith low peak power requiremen-~s~ power controller 130 may be omitted and switches 557 65, 75, 95, 115 and 125 may be replaced, where necessary, with jumpers to reduce the cost of the module and to simplify th~ firmware.
In another embodiment of the subject invention the ROM's and PROM's of boards 42, 52 and 62 may be replaced with battery powered memory modules. By incorporating battery power on boards 43, 52 and 62 addi.tional memory may be added for more sophi.sticated systems without need for a larger power supply. Further, incorporating battery power on boards allows preprogrammed RAM's to be shipped to users for postal rate updates, etc. and the use of only RAM memory with the module of the subject invention simplifies it use in application such as journal printers and electronic accounting systems where RAM storage is needed.
With the availability of low power CMOS logic and low power displays it is possible to extend the idea of battery powered modules to encompa5s entire battery powered modular systems. Such a system is shown in Figure 4. A module in accordance with the su~ject invention 10-500 comprises battery powered paddleboards, 42-500 and 52-500, a battery : ' .

power supply 30-5~0, and incorporates low power CMOS
circuitry ~or acti~e components. A load cell, or other pressure ~ransducer, subsystem 510 utilizing low power circuitry 518 for amplifiers and A/D's is connected to module 10-500 through connector 120-500 and a low power keyboard and display subsystem 530 is connected through connector 70-500~
Suitable low power load cell subsyst~ms are known in the art and include low power modular load cells manu~aetured by the Toledo Scale Division of Reliance Electric Co., Worthington, Ohio, capacitance transducers manufactured by Serta Corp., Massachusetts, and Digital Mass Transducers manufactured by R~
Tron, Arizona Corp., Scottsdale, Arizona. Similarly low power displays and keyboards are available, ranging up to the typewriter type keyboard and multiline display used in the current generation of "laptop" computexs.
Each subsystem includes its own battery power supply 515 and 535; again so that battery30-500 need not be sized to supply the largest system contemplated.
Batteries 30-500, 515 and 535 are interconnected by a low impedance external power bus 550 to reduce noise problems and also to mechanically interconnect the subsystems.
Bus 550 is ormed from a plurality of sub~tantially identical segments 560, shown in Figure 5. Segment 560 comprises two substantial, low i~pedance conductors 562 and 564; for ~5 volts and ground respectively. Conductors 562, 564 are held in parallel, fixed relationship by substantially rigid separator 566. Spaced along conductors 56~ and 564 are polarized sockets 568a and 568b into which various battery , , powered subsystems may be plugged. The sockets are spaced closely enough that multiple connections may be made by each subsystem in order to minimize noise problems.
- The ends 562m, 562f, 564m and 564f are shaped to mate with the corresponding ends of similar segments 560. At one end of separator 566 a captive thumbscrew 570 is mounted and a corresponding tapped bore 572 is provided at the other end so th~t a low impedance mechanically strong bus system may be formed by screwing together a plurality of segments 566.
Mechanical and power connections between the subsystems of a battery power system such as that shown in Figure 4 are made by plugging the subsystems into the bus ~o formed.
Returning to Figure 4 the power drain on bat:teries 30-500, 515 and 535 may be further reduced by provision of switches 25,500 and 125-50 to sequentially connect subsystems as required; substantially in the same manner as described above with respect to the embodiment of Figure 2.
The embodiments of the subject invention described above ~nd showrl in the attached drawings have been yiven by way of illustration vnly. Those skilled in the art will recognize numerous other embodiments w.ithin the scope of the subject invention.

.

,,

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A digital system comprising:
(a)a plurality of modular subsystems, at least one of said subsystems including a battery for supplying power to said system;
(b)connector means for providing signal interconnections between said subsystems;
(c)a common, substantially rigid, extended power distribution bus to which each of said subsystems is mechanically and electrically connected so that the power from said battery is shared by each of said subsystems and said subsystems are mechanically interconnected to form a single unit, said bus further comprising a plurality of modular sections each section comprising;
(c1)a pair of extended conductors for providing positive and negative buses;
(c2)a rigid, insulating element fixed to each of said conductors for holding said conductors in a spaced parallel relationship;
(c3)means for providing mechanical and electrical connection between said conductors and said subsystems; and (c4)a pair of connecting means one at each end of said each section for mechanically and electrically connecting said each section to adjacent similar sections to form said power distribution bus.

2. A digital system as described in claim 1 wherein said system is a postal scale, said scale comprising:
(a)a first modular subsystem, said first subsystem further comprising a load cell, associated electronics for determining the weight of an item to be mailed, and a first battery;
(b)a second modular subsystem, said second subsystem further comprising a microprocessor and associated memory and electronics for controlling said scale and for determining the appropriate postage for said item and a second battery;
(c)a third modular subsystem, said third subsystem further comprising a keyboard and display for providing an operator interface and a third battery.

3. A digital system as described in claim 2 wherein power is supplied to active components of at least some of said subsystems only through said power distribution bus.

4. A digital system as described in claim 2 further comprising switch means for connecting active components of said modular subsystems to said power distribution bus, said switch means being responsive to said microprocessor to selectively connect and disconnect said active components from said bus.

5. A modular section for forming a substantially rigid, extended power distribution bus for mechanically and electrically interconnecting modular subsystems, comprising:
(a)a pair of extended conductors for providing positive and negative conductors;

(b)a rigid insulating element fixed to each of said conductors for holding each of said conductors in a spaced parallel relationship;
(c)means for providing mechanical and electrical connections between said conductors and said subsystems; and (d)a pair of connecting means one at each end of said section for substantially rigidly mechanically and electrically connecting said sections to form said bus.

6. A modular section as described in claim 5 wherein one of said connecting means comprises a captive thumbscrew mounted in said rigid element and the other comprises a matching threaded bore in said rigid insulating element.