User-controlled electronic modification of operating system firmware resident in remote measurement unit for testing and conditioning of

What is claimed:

1. For use with a communication system having a supervisory facility, and one or more remote sites at which respective programmable test devices are located, a respective programmable test device containing a resident test routine operating system for monitoring and testing network lines and subscriber termination equipment coupled thereto, said communication system further including at least one data terminal unit which has the capability of accessing said one or more remote test devices, a method of modifying the test routine operating system resident in the programmable test device of a remote site comprising the steps of:

(a) establishing a communication path between a data terminal unit and said programmable test device;

(b) examining, via said data terminal unit, information stored in said programmable test device, to determine the version level of the resident test routine operating system currently being employed by said programmable test device;

(c) via said data terminal unit, downloading to said programmable test device an upgraded test routine operating system to be employed by said programmable test device as a replacement for the test routine operating system currently being employed by said programmable test device; and

(d) activating, via said data terminal unit, said upgraded test routine operating system, that has been downloaded to said programmable test device in step (b), in place of said resident test routine examined in step (a), so that said upgraded test routine operating system may be executed by said programmable test device.

2. A method according to claim 1, wherein step (a) includes the preliminary step of verifying the availability and transferability of said upgraded test routine operating system by way of said data terminal unit to said programmable test device.

3. A method according to claim 1, wherein step (b) comprises communicating, from said programmable test device to said data terminal unit, information representative of the version level of the currently active test routine operating system of said programmable test device.

4. A method according to claim 3, wherein said programmable test device contains first and second memory systems, said first memory system having stored therein said currently active resident test routine operating system, and said second memory system having an inactive test routine operating system stored therein, and wherein step (c) comprises downloading said upgraded test routine operating system to said second memory system, thereby replacing said inactive test routine operating system stored in said second memory system with said upgraded test routine operating system, and wherein step (d) comprises activating, via said data terminal unit, said upgraded test routine operating system stored in second memory system, in place of the test routine operating system stored in said first memory system, so as to cause said upgraded test routine operating system to be executed by said programmable test device.

5. A method according to claim 4, further including the step of (e) communicating, from said programmable test device to said data terminal unit, information representative of the version level of the replacement test routine operating system resident in said second memory system of said programmable test device.

6. A method according to claim 4, wherein step (e) comprises communicating, from said programmable test device to said data terminal unit, information representative of the contents of said first and second memory systems, so as to verify the version level of the replacement test routine operating system resident in said second memory system of said programmable test device.

7. A method according to claim 4, further including the step (e) of deactivating the replacement test routine operating system resident in said second memory system currently being executed by said programmable test device, and activating said inactive test routine operating system stored in said first memory system for execution by said programmable test device.

8. A method according to claim 4, wherein each of said first and second memory systems is comprised of electronically reprogrammable flash memory.

9. For use with a communication system having a supervisory facility, and one or more remote sites at which respective programmable remote test units are located, a respective programmable remote test unit containing a resident test routine operating system which, when executed, is controllably operative to monitor and test network lines and subscriber termination equipment coupled thereto, said communication system further including at least one data terminal unit which has the capability of accessing said one or more remote test units, a method of modifying a test routine resident operating system in said respective programmable remote test unit comprising the steps of:

(a) establishing a communication path between a data terminal unit and said programmable remote test unit;

(b) examining analyzing, via said data terminal unit, information stored in said programmable remote test unit to identify at least one disabled operational feature and determine which operational features of said active test routine operating system are currently enabled; and

(c) via said data terminal unit, activating at least one disabled operational feature of said active test routine operating system of said programmable remote test unit, so that said at least one activated operational feature may be employed by the active test routine operating system of said programmable remote test unit.

10. A method according to claim 9, wherein step (a) includes the preliminary step of verifying the availability at and transferability from said data terminal device of said disabled operational feature to said programmable remote test unit.

11. A method according to claim 10, wherein step (b) comprises, in response to determining that the test routine operating system currently active in said programmable remote test unit lacks a prescribed operational feature, deactivating the test routine operating system currently active in said programmable remote test unit, and supplying to said programmable remote test unit from said data terminal device signals which cause an upgraded test routine operating system containing said prescribed operational feature to be stored in memory in said programmable remote test unit as a replacement for said test routine operating system currently active in said programmable remote test unit, and activating said upgraded test routine operating system, and wherein step (c) comprises enabling said prescribed operational feature contained within said upgraded test routine operating system in said programmable remote test unit, so that said prescribed operational feature may be employed by the replacement test routine operating system of said programmable remote test unit.

12. A method according to claim 11, wherein said programmable remote test unit contains first and second memory systems, said first memory system storing the currently active resident test routine operating system, and said second memory system storing an inactive test routine operating system, step (b) comprises downloading said upgraded test routine operating system to said second memory system, thereby replacing said inactive test routine operating system stored in said second memory system with said upgraded test routine operating system containing said prescribed operational feature to be employed by said programmable remote test unit as a replacement for the test routine operating system currently active in said programmable test device, and activating, via said data terminal unit, said upgraded test routine operating system that has been downloaded to said second memory system, whereby said upgraded test routine operating system containing said prescribed operational feature is executed by said programmable remote test unit.

13. A method according to claim 12, wherein step (b) further includes communicating, from said programmable remote test unit to said data terminal unit, information representative of the version level of the upgraded test routine operating system replaced in said programmable remote test unit.

14. A method according to claim 12, wherein each of said first and second memory systems is comprised of electronically reprogrammable flash memory.

15. For use with a communication system having a supervisory facility, and one or more remote sites at which respective programmable test devices are located, a respective programmable test device containing a resident operating system which is operative to monitor and test network lines and subscriber termination equipment coupled thereto, said communication system further including at least one data terminal unit which has the capability of accessing said respective programmable test devices, a respective programmable test device containing a first memory system which stores a currently active version of a monitor and test operating system, and a second memory system which stores an inactive version of a monitor and test operating system, a method of deactivating an operational feature contained within the currently active version of a monitor and test operating system stored in said first memory system of said programmable test device comprising the steps of:

(a) establishing a communication path between a data terminal unit and said programmable test device; and

(b) via said data terminal unit, modifying the contents of the operating system stored in said first memory system of said programmable test device, so as to disable an operational feature and thereby prevent the operational feature that has been disabled from being employed in the course of execution of the currently active version of the monitor and test operating system of said programmable test device.

16. A method according to claim 15, wherein step (b) comprises erasing a portion of said second memory system containing said operational feature of said inactive version of said monitor and test operating system, writing, into said portion of said second memory system, a segment of the operating system previously contained in said portion of said second memory system, but with any operational features therein disabled, causing the inactive version of the monitor and test operating system to become the currently active version of the monitor and test operating system of said programmable test device, while deactivating the active version of the monitor and test operating system in said first memory system, and selectively enabling said operational feature of the currently active version of the monitor and test operating system.

17. A method according to claim 15, wherein step (b) comprises erasing a portion of said second memory system containing said operational feature of said inactive version of said monitor and test operating system, writing into said portion of said second memory system a segment of the operating system previously contained in said portion of said second memory system but with any operational features therein not yet enabled, causing the inactive version of said monitor and test operating system to become the currently active version of the monitor and test operating system routine of said programmable test device, while deactivating the active version of the monitor and test operating system in said first memory system, erasing a portion of said first memory system containing said operational feature of said inactive version of said monitor and test operating system, writing into said portion of said first memory system a segment of the operating system previously contained in said portion of said first memory system, but with any operational features therein not yet enabled, and selectively enabling said operational feature.

18. A method according to claim 15, wherein each of said first and second memory systems is comprised of electronically reprogrammable flash memory.

19. For use with a communication system having a supervisory facility, and one or more remote sites at which respective programmable test devices are located, a respective programmable test device containing a resident communication path monitor and test operating system for monitoring and testing network communication links and subscriber equipment coupled thereto, said communication system further including at least one data terminal unit which has the capability of accessing one or more respective programmable test devices, a respective programmable test device containing a first memory system which stores a currently active version of said operating system, and a second memory system which stores an inactive version of said operating system, a method of downgrading the currently active version of said operating system comprising the steps of:

(a) establishing a communication path between a data terminal unit and said programmable test device;

(b) via said data terminal unit, causing a prescribed invalid code to be written into a prescribed portion of the operating system stored in said first memory system within said programmable test device, which prescribed invalid code is effective to declare the version of the operating system stored in said first memory system invalid and prevent its use in the course of an initial default condition of said programmable test device; and

(c) via said data terminal unit, causing said programmable test device to be reset to said initial default condition, in response to which the previously inactive operating system stored in said second memory system becomes a newly currently active operating system executed by said programmable test device.

20. A method according to claim 19, further including the step of (d) communicating, from said programmable test device to said data terminal unit, information representative of the version level of said newly active operating system in said programmable test device.

21. A method according to claim 19, wherein each of said first and second memory systems is comprised of electronically reprogrammable flash memory.

22. For use with a communication system having a supervisory facility, and one or more remote sites at which respective programmable test devices are located, a respective programmable test device containing a resident test routine operating system for monitoring and testing network lines and subscriber termination equipment coupled thereto, said communication system further including at least one data terminal unit which has the capability of accessing said one or more remote test devices, a method of modifying the test routine operating system resident in the programmable test device of a remote site comprising the steps of:

(a) establishing a communication path between a data terminal unit and said programmable test device;

(b) via said data terminal unit, examining information stored in said programmable test device to determine the version of one or more test routine operating systems currently stored in said programmable test device;

(c) via said data terminal unit, replacing the currently active version of a test routine operating system in said programmable test device by a different version of said test routine operating system; and

(d) activating, via said data terminal unit, said different version of said test routine operating system, so that different version of said test routine operating system may be executed by said programmable test device.

23. A method according to claim 22, wherein step (a) includes the preliminary step of verifying the availability and transferability of said different version of said test routine operating system by way of said data terminal unit to said programmable test device.

24. A method according to claim 22, wherein said programmable test device contains first and second memory systems, said first memory system having stored therein said currently active version of said test routine operating system, and said second memory system having said different version of said test routine operating system stored therein, and wherein step (d) comprises activating said different version of the test routine operating system resident in said second memory system in said programmable test device, and causing said different version of said test routine operating system to be executed by said programmable test device.

25. A method according to claim 24, wherein said step (c) comprises erasing said second memory system and downloading, from said supervisory facility to the erased second memory system, said different version of said test routine operating system.

26. A method according to claim 25, wherein said step (d) comprises causing said programmable test device to be reset and, upon being reset, to default to said second memory system containing said different version of said test routine operating system, so that different version of said test routine operating system may be executed by said programmable test device.

27. A method according to claim 26, wherein each of said first and second memory systems is comprised of electronically reprogrammable flash memory.

28. A method according to claim 26, wherein step (d) comprises marking the version of the operating system stored in said first memory system with an invalid code, so as to declare the version of the operating system stored in said first memory system invalid and prevent its use in the course of causing said programmable test device to be reset, whereby said programmable test device, upon being reset, will default to said second memory system containing said different version of said test routine operating system, so that different version of said test routine operating system may be executed by said programmable test device.

29. A method according to claim 22, wherein step (c) comprises replacing the currently active version of a test routine operating system in said programmable test device by an upgraded version of said test routine operating system.

Description Submit all comments and votes

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention relates to subject matter disclosed in co-pending application Ser. No. 08/194,203, filed coincident herewith, entitled: "Local/Remote Modification of Electronically Alterable Operating System Firmware Resident in Redundant Flash Memory of Remote Unit for Testing/Conditioning Subscriber Line Circuits," by E. Siu et al, assigned to the assignee of the present application and the disclosure of which is herein incorporated.

FIELD OF THE INVENTION

The present invention relates in general to communication systems, such as telephone systems, and is particularly directed to a mechanism for controllably electronically modifying the functionality of measuring and test routine, contained within a remote, programmable test device, which is operative to monitor and test network lines and subscriber termination equipment coupled thereto, without the need for on-site, physical access, and removal and replacement of digital processor and memory circuitry of the test device.

BACKGROUND OF THE INVENTION

Measuring and test equipment currently employed by telephone service providers customarily contains a variety of conditioning and signal generation functions which enable service and maintenance personnel to apply a prescribed number of electrical stimuli to a line, such as a (digital) subscriber loop, for the purpose of trouble-shooting the line and measuring its performance. A non-limitative example of such equipment is diagrammatically illustrated in FIG. 1, which shows the distribution of a plurality of (microprocessor-controlled) remote measurement units (RMUs) 11, which are installed at a plurality of sites geographically remote with respect to each other and a supervisory site 12.

An RMU 11 includes various components, such as tone generation and electrical conditioning circuitry which, under the control of a firmware-resident measurement and test mechanism contained in the resident operating system employed by an on-board processor, selectively transmit prescribed test signals to the line, and may also condition the line with electrical circuit parameters, that allow an associated line measurement unit to conduct line measurements and thereby determine the current state of the line and its ability to successfully perform as intended.

For this purpose, each RMU 11 is typically of the type that conforms to computer interface requirements defined in Issue 3 of AT&T Publication KS-23253 and contains internal firmware, which is operative to perform various diagnostic or test operations on network lines 13 and (subscriber) termination equipment 15. The RMU may be accessed by means of one or more video display terminals (VDTs), or data terminal units (DTUs) 21 at the supervisory site 12, which have the capability of accessing the remote test equipments 11 through attendant modem devices 23, such as industry standard Hayes `AT`-compatible 300/1200 units, that are linked to a central office 25.

Because test and conditioning parameters and customer-requested performance features may differ among various pieces of equipment, whenever it is necessary to perform a repair, or effect a change to the functionality of the firmware (e.g. change an instruction set), it is customary practice for a service technician (craftsperson) to travel to the site where the equipment is installed, and either make a component or board replacement in the field, or, as is more often the case, retrieve the unit, bring it back to a servicing site, where a repair or retrofit is performed, and then return the modified unit to the remote site, so that it may be placed back in service.

SUMMARY OF THE INVENTION

In accordance with the present invention, the costs in labor and down time required to service a remote test unit in the manner described above are substantially reduced by configuring the firmware-memory architecture of the unit's micro-controller of a pair of redundant, erasable flash memory systems, that enable the operating system firmware of a remote monitoring unit to be selectively, electronically modified, in particular erased, replaced and features selectively turned on, from a supervisory device (e.g. a data terminal coupled via an attendant modem to the central office, or via a personal computer connection to a serial port (e.g. RS-232 port) of the test unit).

More particularly, pursuant to the present invention, associated with the resident control processor of the remote measurement and test unit (RMU) are two memory systems, which respectively store electronically modifiable active and inactive `quasi-redundant` versions of the micro-controller's system software. By `quasi-redundant` is meant that each memory system contains a version of the operating system firmware that is potentially capable of operating the RMU. To provide for remote electronic reprogrammability each memory system is configured of one or more flash memory devices. When an RMU is powered up or reset, a reset routine described in detail in the above-identified co-pending application ensures that the `correct` one of the two quasi-redundant systems available to the RMU's microcontroller will become the operating system.

Normally, after a modification, the `correct` system is the previously off-line system that has been changed. However, should this modified inactive system contain an anomaly that will prevent successful operation of the test device, it is necessary that the inactive system remain off-line and the unit continue to operate with the currently running version of the firmware. In accordance with the invention described in the above-identified co-pending application, these objectives are achieved by the use of a prescribed reset routine and by structuring the contents of the modified inactive memory system to include a precursor set of instruction code that prevents an accidental boot-up from the off-line system (in which one or more memory systems have been erased) and thereby avoids anomalous operation of the RMU.

For this purpose, a precursor section of common code memory space is loaded with an instruction sequence that forces the off-line system, if accessed, to perform a continuous no operation loop. Whenever the RMU begins executing the firmware in either system, a time-out clock is started. Unless the operating system code, which is PG,7 located in memory address space immediately following the no operation loop, begins executing prior to expiration of the time-out, a switch to the other operating system is performed.

Once transfer of modified (e.g. upgraded) software to the designated bank(s) of the inactive system has been completed, the host processor in the user's data terminal unit commands the RMU to reset itself. With the RMU containing two different versions of the operating system, one of which is the newer version and the other of which is the previously active routine which is to go off-line, the reset routine described in the above-referenced co-pending application is executed to ensure that the `correct` one of the two quasi-redundant systems available to the RMU's microcontroller will become the operating system.

When an RMU is initially installed, each of its flash memory systems contains the same firmware version of the operating system, so that the operating system firmware in each memory system is a duplicate of the other. Except for activating an installed feature, when a modification is to be made to the RMU's firmware, it is the off-line or inactive version in the redundant memory system that is changed. After a change has been completed, the system is reset and the changed version is activated, while the previously running version is deactivated.

In accordance with a first aspect of the present invention, which involves remotely, electronically performing an `upgrade` of operating system firmware in an RMU, it is necessary to install a newer version of the operating system firmware than the one currently running. Since an upgrade involves an enhancement to equipment functionality, for each RMU user, a functionality/use descriptor file, which contains information as to what firmware version a unit currently contains and what features it is permitted to use, is initially accessed. The functionality/use descriptor file is effectively a permission and capability file that tells the installer what may and what may not be installed for a particular RMU. Access to this file allows an upgrade installer to determine whether a requested upgrade may be performed. If an upgrade to a specified RMU is permitted, a communication is established between the (host processor of the) accessing terminal unit and the RMU.

Once connectivity with the destination RMU has been established, the host processor requests a copy of a bank descriptor table contained in the RMU. The bank descriptor table details the contents of the firmware versions currently stored in the respective flash memory systems of the RMU. The contents of the bank descriptor table are analyzed by the remote control (host) processor in order to facilitate the transfer or downloading of only those portions of firmware that are necessary to effect the requested upgrade.

Since modification of the contents of flash memory requires an erasure of a complete block or bank of memory and then a rewriting of new data into the erased memory space, the host processor next proceeds to erase each block of flash memory of the `inactive` operating system which is to receive a `target` firmware upgrade. The upgrade software is then written into the erased blocks of the inactive memory. Once the transfer of the upgraded software to the designated blocks of inactive system is completed, the RMU is commanded to activate the newly downloaded software upgrade in the inactive system and deactivate the currently active system containing the previous version.

After the operational feature set available for use by the RMU is turned-on, the RMU is commanded to reset itself, which causes its internal processor to default to that memory system which is not marked invalid and contains the highest version of operating system firmware, that the reset routine has determined is operationally valid and not in downgraded status. At any given time, only one memory system can be marked invalid.

After being reset, the RMU begins executing the upgraded version of its operating system, and the host processor terminates the connection to the RMU. The final step of an upgrade is for the host processor to reconnect with the RMU and request a copy of the bank descriptor table contained, in order to verify that the RMU is currently running the upgraded firmware.

A second aspect of the invention is directed to performing a `downgrade` of existing RMU firmware, whose purpose is to invalidate the currently running version of the operating system in the active memory system and to activate the `quasi-redundant` version of the operating system resident in the inactive memory system. Downgrading an operating system version implies that an upgrade has previously taken place, the currently running version of operating system firmware being the upgraded version, and the inactive memory system containing an earlier version of the operating system.

As is the case with an upgrade, once a communication has been established between the host processor of the accessing terminal unit and an addressed RMU, the host processor commands the RMU processor to mark the currently running system as invalid and commands the RMU to reset itself, whereby the RMU's control processor defaults to that memory system which contains the previously inactive version of its operating system, which is not marked invalid. After transmitting a reset and terminating the connection, the host processor re-establishes a connection with the RMU and requests a copy of the bank descriptor table to verify that the RMU is currently running the previously inactive firmware version.

Pursuant to a third aspect of the invention, one or more features of the firmware may be selectively activated. To activate a feature (which is similar to an upgrade in that it involves an enhancement to the functionality of the currently active program), it is necessary to turn on one or more programmable features contained within the active system, but not currently allowed to be used by the RMU. Until activated, operational features are invisible to the RMU processor. Associated with each operational features of a respective firmware version is a status bit, which is one (`1`) when the firmware is initially installed. Activation of a feature involves switching the state of the feature bit from a first logical state (e.g. a logical `1`) to a second logical state (e.g. a logical `0`).

Each remotely switchable feature status bit is preferably contained in a feature status table stored in a prescribed portion of memory. For example, to accommodate up to sixteen features, a pair of sequential feature bytes may be employed. Via a virtual to physical map associated with the feature byte, the user may delineate which feature or features are to be selectively enabled in the active system. With flash memory, programming a memory bank involves first erasing the entire bank and then changing the erased states of selected memory cells. Thus, when a feature is to be enabled or switched on, it's status bit in the feature table is changed from its original reset state `1` to an active state `0`.

Like an upgrade, since the routine employed for feature activation involves an enhancement to equipment functionality, the functionality/use descriptor file is first examined to whether a requested feature is available. If activation of the requested feature is not permitted or if the feature is not available the routine is terminated. If the requested feature is available a communication is established between the accessing terminal unit and the RMU. The host processor requests a copy of the bank descriptor table contained in the RMU and analyzes the table in order to determine whether the currently running firmware version contains the requested feature(s). If the currently running version does not contain the feature to be activated, then an upgrade to a software version containing the requested feature is performed. If the currently active system contains the requested feature(s), the host processor commands the RMU to activate the feature by changing the logic state of the appropriate feature switch bit, thereby making the feature available for use in the currently active system. Once the requested feature activation is complete, the host processor goes back on-hook.

A further aspect of the invention involves the ability to selectively `deactivate` one or more features of a currently running system. This aspect of the invention may be employed when it is necessary to turn off or disable a feature that has been previously enabled, for example in the case of a feature that was inadvertently turned on when the operating system was originally installed.

For this purpose, once connectivity with the destination RMU has been established, the host processor commands the RMU to erase each block of flash memory of the `inactive` system which contains a feature to be deactivated. It then commands the RMU to rewrite the software (with no features turned on) into its associated blocks of flash memory of the RMU's inactive operating system. Once a rewrite of the software to the designated blocks of inactive bank has been completed in the inactive memory bank, the host processor commands the RMU to reset itself and reverses the states of the two memory systems, thereby making the inactive system where the reset features reside active, and the currently running system inactive.

The host processor next commands the RMU to erase each block of flash memory of the `inactive` system, which contains a feature to be deactivated, and commands the RMU to rewrite the software (with no features turned on) into its associated blocks of flash memory of the RMU's inactive bank. The host processor then commands the RMU to activate selected features (excluding those to remain deactivated) by changing the logic state of the appropriate feature switch bit from its initially erased state to an opposite logical state, thereby making the non-deactivated features available for use in the currently active system. Once the requested feature activation is complete, the host processor terminates the connection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 diagrammatically shows the distribution of a plurality of microprocessor-controlled remote measurement units installed at a plurality of sites geographically remote with respect to each other and a supervisory site;

FIG. 2 diagrammatically illustrates the architecture of the micro-controller of an RMU having system bus, control processor, random access memory, an input/output interface unit, and firmware flash memories;

FIG. 3 is a process flow routine of the steps carried out for upgrading the existing firmware in an RMU;

FIG. 4 is a process flow routine of the steps carried out for downgrading the existing firmware in an RMU;

FIG. 5 is a process flow routine of the steps carried out for activating one or more features of the currently running firmware in an RMU; and

FIG. 6 is a process flow routine of the steps carried out for deactivating one or more features of the currently running firmware in an RMU.

DETAILED DESCRIPTION

Before describing in detail the test routine modification mechanism in accordance with the present invention, it should be observed that the present invention resides primarily in what is effectively the installation of a pair of flash memory systems in a remote test unit, in which respective active and inactive quasi-redundant versions of operating system firmware are stored, together with an augmentation of the control software employed by a `master` test system controller (host processor) and the micro-controller within a programmable monitor and test unit, which permit a host processor to selectively establish a control link with and selectively alter the functionality of a subscriber line measuring and test operative system contained within a `slave` test device, without the need for on-site, physical access, and removal and replacement of digital processor and memory circuitry of the test device.

Consequently, the configuration of such a remote test unit and the manner in which it is interfaced with other communication equipment of the telephone network have been illustrated in the drawings by readily understandable block diagrams, which show only those specific details that are pertinent to the present invention, so as not to obscure the disclosure with details which will be readily apparent to those skilled in the art having the benefit of the description herein. Thus, the block diagram illustrations of the Figures are primarily intended to illustrate the major components of the system in a convenient functional grouping, whereby the present invention may be more readily understood.

Various aspects of the test routine modification mechanism of the present invention will be described with reference to FIGS. 3-6, which show respective operating system modification flow routines, the execution of which is operative to modify the functionality of a measuring and test operating system, contained within an RMU, without the need for on-site, physical access, and removal and replacement of digital processor and memory circuitry of the test device.

As pointed out above, in order to enable the present invention to controllably modify, electronically from a remote site, the operating system firmware employed by the telephone line monitor and test unit, the architecture of the processor board within the test unit contains a plurality (pair) of flash memory systems, which store respective electronically modifiable active and inactive versions of the micro-controller's firmware (as opposed to the conventional use of a single dedicated read-only memory module to store a non-modifiable version of the unit's firmware).

For this purpose, as diagrammatically illustrated in FIG. 2, coupled with the test unit's system bus 41 are a control processor 43, attendant random access memory (RAM)