Patent Publication Number: US-7904671-B2

Title: Method regarding a memory device for a programmable logic controller (PLC)

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a divisional of, claims priority to, and incorporates herein by reference in its entirety, pending U.S. Non-Provisional patent application Ser. No. 10/685,821 titled “Method for Utilizing a Memory Device for a Programmable Logic Controller (PLC)”, filed 15 Oct. 2003, which claims priority to the following U.S. Provisional Patent Applications: 
     60/436,252, filed 23 Dec. 2002, and 
     60/436,249, filed 23 Dec. 2002. 
    
    
     BACKGROUND 
     Commercially available programmable logic controllers (PLC&#39;s) can be supplied with a memory device for storage. The memory device, which can be a memory cartridge, is most often an electronically erasable programmable read only memory (EEPROM) device. Common methods of using the memory cartridge include the storage of PLC configuration and programming information. 
     U.S. Pat. No. 5,727,170 (Mitchell) allegedly cites: “[t]he PLC has a user configurable protocol port attached thereto. Briefly stated, at the PLC communication port or as a result of a user program or input/output I/O event, a special flag bit may be set which thereby allows the communication port to be activated. This is done by the flag bit causing an interrupt to occur in the PLC user program which allows a user to communicate with a user specified protocol scheme rather than the normal communication/programming protocol when this special bit is not set.” See Abstract. 
     U.S. Pat. No. 5,485,590 (Hyatt) allegedly cites: “[a] module interfaces a programmable controller to several serial communication networks over which data may be exchanged according to different protocols. A module has a central controller and a separate port circuit for each of the networks. Each port circuit includes a microprocessor and a shared memory to which both the central controller and the port microprocessor have access for the exchange of data. The central controller transfers data from the shared memories to a module output coupled to other components of the programmable controller. A removable memory cartridge stores a plurality of programs for execution by the port microprocessors to exchange data over the networks using different communication protocols. Configuration data is stored in the module defining which program is to be transferred from the memory cartridge into the shared memory of each port circuit. Protocol parameter configuration inquiries are stored for each program so that the user can be queried to select values for the parameters of the communication protocol used by the program.” See Abstract. 
     U.S. Pat. No. 5,991,510 (Beaulieu) allegedly cites “A robot drive has operating and configuration parameters at an installation location stored in an easily removable storage device on the drive, or nearby, so that special data, such as that associated with arm design and system layout, including taught stations, can remain associated with the drive and installation whereby the drive system can be installed or replaced in minimal time since the storage device does not need reprogramming. This removable storage device, in the form of a static memory or Master Key, e.g., a Dallas Key or E Prom or the like, may be affixed to the robot body or off board nearby, and may store arm design parameters, programmed while on the robot body or off-line, and becomes a unique part structured for manufacturing with respect to the arm set design. Further, nominal system layout parameters can be prestored in the Key, and when this Key is affixed to the robot drive, the robot automatically has the information regarding both arm design and system layout, which will help avoid collisions and provide a starting point for the fine teaching of the transfer stations. Additionally, the fine location parameters for each transfer station may be stored in the Key when the robot is installed. Thus, the Key will contain all the information needed to make a robot unique to a unique system, and when a robot drive is replaced, by affixing the original Key to the new robot or nearby, it will assume all of the parameters of the initial robot.” See Abstract. 
     U.S. Pat. No. 4,937,419 (Kolodziej) allegedly cites “[a] programmable weld and machine controller for use in controlling a welding machine. The controller includes a central processing unit containing a stored control program connected to a memory which operates both the welding operation of the machine as well as the operation of the machine itself. The controller receives inputs from the machine in its various operational states as well as a data entry and display unit and a current monitor of the welding operation which generates outputs through a heat controlled output to activate a firing circuit to control the welding operation. Back-up of the memory program may be attained through an accessory port to a memory back-up storage unit.” See Abstract. 
     SUMMARY 
     Certain exemplary embodiments can provide a method for utilizing a memory cartridge connected to a PLC. The memory cartridge can comprise a plurality of memory segments. The method can comprise a plurality of activities comprising: providing a default identifying stamp for records in a data log file, a structure for the data log file stored separately from the data log file in the memory cartridge, and obtaining a request to provide the data log file. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention and its wide variety of potential embodiments will be more readily understood through the following detailed description, with reference to the accompanying drawings in which: 
         FIG. 1  is a block diagram of an exemplary embodiment of a system  1000 ; 
         FIG. 2  is a block diagram of an exemplary embodiment of a data structure  2000 ; 
         FIG. 3  is a flowchart of an exemplary embodiment of a method  3000 ; 
         FIG. 4  is a flowchart of an exemplary embodiment of a method  4000 ; 
         FIG. 5  is a flowchart of an exemplary embodiment of a method  5000 ; 
         FIG. 6  is a flowchart of an exemplary embodiment of a method  6000 ; 
         FIG. 7  is a flowchart of an exemplary embodiment of a method  7000 ; 
         FIG. 8  is a flowchart of an exemplary embodiment of a method  8000 ; and 
         FIG. 9  is a block diagram of an exemplary embodiment of an information device  9000 . 
     
    
    
     DETAILED DESCRIPTION 
     As used herein, an I/O device can comprise any sensory-oriented input and/or output device, such as an audio, visual, tactile (including temperature, pressure, pain, texture, etc.), olfactory, and/or taste-oriented device, including, for example, a monitor, display, keyboard, keypad, touchpad, pointing device, microphone, speaker, video camera, camera, scanner, and/or printer, potentially including a port to which an I/O device can be attached or connected. 
     As used herein, render means made perceptible to a human, for example as data, commands, text, graphics, audio, video, animation, and/or hyperlinks, etc., such as via any visual and/or audio means, such as via a display, a monitor, electric paper, an ocular implant, a speaker, a cochlear implant, etc. 
     As used herein, an information device can be any general purpose and/or special purpose computer, such as a personal computer, workstation, server, minicomputer, mainframe, supercomputer, computer terminal, laptop, wearable computer, and/or Personal Digital Assistant (PDA), mobile terminal, Bluetooth device, communicator, “smart” phone (such as a Handspring Treo-like device), messaging service (e.g., Blackberry) receiver, pager, facsimile, cellular telephone, a traditional telephone, telephonic device, a programmed microprocessor or microcontroller and/or peripheral integrated circuit elements, and application-specific integrated circuit (ASIC) or other integrated circuit, a hardware electronic logic circuit such as a discrete element circuit, and/or a programmable logic device such as a programmable logic device (PLD), programmable logic array (PLA), field programmable gate array (FPGA), or programmadble array logic array (PAL) circuit, or the like, etc. In general any device on which resides a finite state machine capable of implementing at least a portion of a method, structure, and/or or graphical user interface described herein may be used as an information device. An information device can include well-known components such as one or more network interfaces, one or more processors, one or more memories containing instructions, and/or one or more input/output (I/O) devices, etc. 
       FIG. 9  is a block diagram of an exemplary embodiment of an information device  9000 . Information device  9000  can comprise a network interface  9100 . Network interface device  9100  can comprise a telephone, a cellular phone, a cellular modem, a telephone data modem, a fax modem, a wireless transceiver, an ethernet card, a cable modem, a digital subscriber line interface, a bridge, a hub, a router, or other similar device. Information device  9000  can be connectable directly and/or indirectly to other information devices via network interface  9100 . 
     Information device  9000  can further comprise a processor  9200 . Processor  9200  can be a central processor, a local processor, a remote processor, parallel processors, and/or distributed processors, etc. The processor can be a general purpose microprocessor, such the Pentium III series of microprocessors manufactured by the Intel Corporation of Santa Clara, Calif. In another embodiment, the processor can be an Application Specific Integrated Circuit (ASIC) or a Field Programmable Gate Array (FPGA) that has been designed to implement in its hardware and/or firmware at least a part of an embodiment disclosed herein. Processor  9200  can make information device  9000  adaptable to perform according to a plurality of instructions. 
     Information device  9000  can further comprise a memory  9300 . Memory  9300  can comprise any device capable of storing analog or digital information, for example, a non-volatile memory, volatile memory, Random Access Memory, (RAM), Read Only Memory (ROM), flash memory, magnetic media, a hard disk, a floppy disk, a magnetic tape, an optical media, an optical disk, a compact disk (CD), a digital versatile disk (DVD), and/or a raid array, etc. The memory can be coupled to a processor and can store instructions adapted for execution by the processor according to an embodiment disclosed herein. Memory  9300  can be adaptable to store instructions  9400 . 
     Instructions  9400  can comprise a plurality of instructions written in a machine readable language. Instructions  9400  can be adaptable to process information when executed by processor  9200 . In an operative embodiment, information used by processor  9200  using instructions  9400  can provide information to and/or be modified by the processing operation. 
     Information device  9000  can further comprise an I/O device  9500 . I/O device  9500  can be adaptable to allow information device  9000  to communicate directly and/or indirectly with other information devices and/or users. 
       FIG. 1  is a block diagram of an exemplary embodiment of a system  1000 . As illustrated, system  1000  can comprise a controller, such as a programmable logic controller (PLC)  1200 . System  1000  can comprise a machine and/or process monitorable and/or controllable by PLC  1200 . System  1000  can further comprise hardware and/or software adaptable to allow a user to communicate with PLC  1200 . PLC  1200  can be a commercially purchased PLC. Alternatively, PLC  1200  can be an information device. PLC  1200  can be used to monitor and/or control a process, such as an industrial process. For example, PLC  1200  can monitor and/or control an alarms indicator, relay, sensor, another controller, and/or a motion device, such as a motion controller, such as a stepper motor controller, a servo controller, an actuator controller, etc.; a motion drive, such as a stepper drive, servo drive, etc.; and/or an actuator, such as a stepper motor, servomotor, linear motor, motor, ball screw, servo valve, hydraulic actuator, pneumatic valve, etc. 
     PLC  1200  can include a central processing unit (CPU) via which instructions are processed and appropriate control signals determined. PLC  1200  can further comprise and/or be coupled to an input-output (I/O) device. The I/O device can render information obtained from PLC  1200 . The user also can interact with PLC  1200  via the I/O device. As used herein interact means receiving alerts or notifications, revising or switching programs, examining control algorithms, and/or modifying graphics displays, etc. 
     A memory device, such as a memory cartridge  1100  can be couplable to PLC  1200 , either directly or via a network. In certain embodiments, memory cartridge  1100  can be insertable into PLC  1200  and/or directly connectable to PLC  1200 . The memory device can be non-volatile memory, volatile memory, ROM, random access memory, flash memory, magnetic media, a hard disk, a floppy disk, a magnetic tape, an optical media, an optical disk, a CD, a DVD, and/or a raid array, etc. The memory device can provide storage for instructions or data usable by the PLC&#39;s CPU. 
     In an exemplary embodiment, PLC  1200  can be couplable to a user interface device  1300  via a network  1600 . Network  1600  can be a public, private, circuit-switched, packet-switched, virtual, radio, telephone, cellular, cable, DSL, satellite, microwave, AC power, twisted pair, ethernet, token ring, LAN, WAN, Internet, intranet, wireless, Wi-Fi, BlueTooth, Airport, 802.11a, 802.11b, 802.11g, and/or any equivalents thereof, etc. 
     Via user interface device  1300 , the user can interact with PLC  1200 . User interface device  1300  can be an information device. For example, via user interface device  1300 , the user can monitor a process, connectable to and/or controllable by PLC  1200 . The user also can interact with PLC  1200  via user interface device  1300 . 
     Via network  1600 , PLC  1200  can be further couplable to a process element  1400 . Process element  1400  can comprise a machine tool, a robot, a chemical reactor, a stove, a furnace, an assembly machine, a packaging machine, and/or piece of conveying equipment, etc. In an operative embodiment, process element  1400  can be controlled, influenced, and/or monitored via PLC  1200 . 
     The PLC can be further communicable with the user via network interface device  1500 . Network interface device  1500  can be a telephone, a cellular phone, a modem, a cellular modem, a telephone data modem, a fax modem, a wireless transceiver, an ethernet card, a cable modem, a digital subscriber line interface, a bridge, a hub, a router, or other similar device. Network interface device  1500  can be adaptable to allow the user to communicate with PLC  1200  while located remotely from the PLC  1200 . Via a network interface device  1500 , network  1600  can be further couplable to a peripheral network  1700 . Peripheral network  1700  can be a public, private, circuit-switched, packet-switched, virtual, radio, telephone, cellular, cable, DSL, satellite, microwave, AC power, twisted pair, ethernet, token ring, LAN, WAN, Internet, intranet, wireless, Wi-Fi, BlueTooth, Airport, 802.11a, 802.11b, 802.11g, and/or any equivalents thereof, etc. etc. 
     Peripheral network  1700  can be further connectable to a remote user interface device  1800 . Remote user interface device  1800  can be an information device comprising an I/O device. In an operative embodiment, peripheral network  1700  can be adapted to allow the user to interact with PLC  1200 . Peripheral network  1700  can allow the user to interact with PLC  1200  from a location hundreds or even thousands of miles away from PLC  1200 . Peripheral network  1700  can be usable to enhance availability and reduce programming, managerial, and/or maintenance costs attributable to PLC  1200  and/or the monitoring and/or control of process element  1400 . Process element  1400  can be one of a plurality of process elements. 
       FIG. 2  is a block diagram of an exemplary embodiment of a data structure  2000 . An exemplary embodiment of data structure  2000  can comprise a project file  2100 . Project file  2100  can be storable on a memory device, such as the memory cartridge. Project file  2100  can comprise a program  2200 , a recipe  2300 , information indicative of a data log file structure  2400 , information indicative of a recipe structure  2500 , and/or a support document  2600 , etc. Data log file structure  2400  can be stored separately from a corresponding data log file, which can be stored on any memory device. Recipe structure  2500  can be stored separately from a corresponding recipe  2300 . Project file  2100 , and/or one or more elements thereof, can be adaptable to allow the PLC to monitor and/or control a process element. 
     Program  2200  can comprise a set of machine-readable instructions. Program  2200  can be transferable to the PLC. Program  2200  can be executable on the PLC. Program  2200  can be storable in project file  2100 . In an operative embodiment, program  2200  can be adapted and/or adaptable to facilitate the performance of tasks by the PLC such as displaying a process flow, transferring information, storing information, processing information, prompting a user for input, controlling a process variable, and/or reporting a process output, etc. 
     Recipe  2300  can comprise at least one of a plurality of input values, each input value from the plurality of input values corresponding to a process variable. Each process variable can be used to monitor and/or control a process via a PLC. Recipe  2300  can comprise values for settings such as: machine speed, machine size, product type, product composition, product size, product labeling, package type, package size, package labeling, a pressure, a temperature, and/or any other relevant process parameter. Recipe  2300  can be storable in project file  2100 . Recipe  2300  can be communicable to provide settings to program  2200  in order to render a product makable and/or a process operable using the PLC. Alternatively, recipe  2300  can be communicable to a different processing device and/or software to provide settings to render a product makable and/or process operable. 
     Information indicative of the data log structure  2400  can comprise a symbolic representation of how a data log file is formatted for storage and retrieval. Information indicative of the data log file structure  2400  can be storable in project file  2100 . Information indicative of the data log file structure  2400  can comprise a series of values and/or characters correlatable to structural characteristics of the data log file. The data log file and/or the information indicative of the data log structure  2400  can be storable on the memory cartridge or on another memory device. Information indicative of the data log file structure  2400  can be adaptable to render the data log file machine-storable and/or machine-readable. Information indicative of the data log file structure  2400  can be storable separately from the data log file. 
     Information indicative of the recipe structure  2500  can comprise a symbolic representation of how the recipe is formatted for storage and retrieval. Information indicative of the recipe structure  2500  can be storable in project file  2100 . Information indicative of the recipe structure  2500  can comprise a series of values and/or characters correlatable to structural characteristics of the recipe. Information indicative of the recipe structure  2500  can be adaptable to render the recipe machine-storable and/or machine-readable. Information indicative of the recipe structure  2500  can be storable separately from the recipe. 
     Support document  2600  can comprise a textual and/or visual representation of information assimilatable to improve understanding of the PLC, the memory cartridge, hardware components related to the PLC, software components related to the PLC, and/or the controlled process, etc. Support document  2600  can be storable in project file  2100 . In an exemplary embodiment, support document  2600  can be reviewable by the user at the user interface device in order to facilitate understanding and/or modifying the PLC, hardware related to the PLC, software related to the PLC, the process, the project file, the data log file, information indicative of the structure of the data log file, the recipe, and/or information indicative of the structure of the recipe, etc. Alternatively, support document  2600  can be rendered to the user via an I/O device connectable to an information device. 
       FIG. 3  is a flowchart of an exemplary embodiment of a method  3000  for using the memory device. At activity  3100 , a beginning memory segment on the memory cartridge can be located where the project file or any component thereof can be read from and/or written. Alternatively, the beginning memory segment can be located on the memory device. In an operative embodiment, the project file can occupy a single memory segment. Alternatively, in an operative embodiment, the project file can occupy a plurality of memory segments. 
     At activity  3200 , the project file can be provided to the memory cartridge. Alternatively, the project file can be provided to the memory device. Providing the project file to the memory device can allow information contained in the project file to be subsequently transferred to the PLC. For example, in case of a power failure erasing volatile memory in the PLC, certain information erased from volatile memory can be restorable from the project file stored in the memory device. 
       FIG. 4  is a flowchart of an exemplary embodiment of a method  4000  for using the memory device. At activity  4050 , the user can request to obtain (e.g., view, hear, have rendered, and/or obtain access to) information stored and/or storable on a memory device. The information can comprise programming code, programming code documentation, support documentation pertaining to hardware and/or software relatable to the PLC, process data, recipe code, and/or recipe information, one or more data logs, etc. The user can potentially improve monitoring, control, and/or management of the PLC and/or at least one process element with the obtained information. 
     At activity  4100 , the user can be prompted to select a language for rendering the information from a plurality of language choices. The user can be allowed to provide a selection corresponding to a selected language. The user can be allowed to make a selection on an I/O device connectable to an information device. Language choices can comprise any language, such as English, German, French, Italian, Spanish, and/or Chinese, etc. The user can select the language by providing a user input corresponding to a selected language. 
     At activity  4200 , the user input can be received corresponding to a selected language. The user input can be received as a result of a user interacting with an I/O device connected to an information device. The user input can improve communicability of information to and/or from the PLC via transferring the information in a language favored and/or better understood by the user. 
     At activity  4300 , the information can be located on the memory device. The information can be located by the actions of the PLC or any information device directly and/or indirectly connectable to the PLC. Locating the information can facilitate communications between the user and the PLC. 
     At activity  4400 , the information can be provided to the user responsive to the user input corresponding to the selected language. The information can be provided, in the selected language, to the user interface device. Alternatively, the information can be provided, in the selected language, to any I/O device and/or any information device. 
       FIG. 5  is a flowchart of an exemplary embodiment of a method  5000  for using the memory device. At activity  5100 , a first identifying stamp can be provided for a data log record. The first identifying stamp can comprise a calendar date and/or a clock time associated with requesting, collecting, receiving, and/or recording the data log record. Alternatively, the first identifying stamp can relate to a process unit, such as a machine, instrument, and/or device, etc., associated with a data log record. For example, the first identifying stamp can be a process unit identifier, such as a machine number, a sensor number, and/or an actuator number, etc. In an operative embodiment, the process identifying stamp can assist the user in analyzing and categorizing data log records. 
     At activity  5200 , the PLC can allow the user to select a second identifying stamp from a plurality of choices. Identifying stamp choices can comprise various date and/or time elements comprising a year, a month, a day, a day of week, an hour, a time zone, a minute, a second and/or a portion of a second, etc. Alternatively, the second identifying stamp can comprise various numbers and/or symbols relatable to the process unit. 
     At activity  5300 , a user input corresponding to a selection of the second identifying stamp can be received from the selection device. The second identifying stamp can improve the user&#39;s ability to analyze the process log record. Alternatively, the second identifying stamp can reduce storage space requirements for a data log record by providing a smaller second identifying stamp as compared to the first identifying stamp. 
     At activity  5400 , the selected second identifying stamp can be provided to the memory device responsive to the user input. In an operative embodiment providing the second identifying stamp to the memory device can supply information to the user, when the user subsequently analyzes the data log record, information within the second identifying stamp can be adaptable to improve the efficiency of analyzing, sorting, and/or otherwise processing information in the data log record. 
       FIG. 6  is a flowchart of an exemplary embodiment of a method  6000  for using the memory device. At activity  6100 , a first setting can be provided corresponding to an instruction to erase or to not erase the data log from the memory device after the data log is read. The instruction to erase or not erase the data log file subsequent to reading the data log file can allow a user to more effectively manage data storage and retrieval on the memory device. Erasing the data log file can provide an assurance that no data log record on the memory device has been previously read. 
     At activity  6200 , the user can be allowed to select a second setting corresponding to an instruction to erase or to not erase the data log from the memory device after the data log is read. The second setting can provide instructions contrary to the first setting. Providing the second setting can allow the user improved control over data storage resources. 
     At activity  6300 , the data log can be read from the memory device. The data log can then be erased or not erased from the memory device responsive to the user input. Reading the data log can allow the user to transfer information for additional processing and/or storage responsive to needs to analyze and/or improve the monitoring, control, and/or reporting of the process element controllable by the PLC. 
       FIG. 7  is a flowchart of an exemplary embodiment of a method  7000  for using the memory device. At activity  7100 , the user can be prompted allowed to select elements of a project file for storage on the memory device. The selectable elements can comprise the project file, the program, the recipe, information indicative of the recipe structure, information indicative of the data log file structure stored separately from the data log file, and/or support documentation pertaining to the process, the PLC, hardware related to the PLC, and/or software related to the PLC. 
     At activity  7200 , a user input corresponding to an option to store at least one project file element can be received from the selection device. Providing the user with storage options can allow the user to customize a storage plan to suit unique system requirements taking into consideration such factors as: other means for storing the project file, the size of the memory cartridge, the amount of process data collected for storage in the data log file, the frequency of storing process data collected for storage in the data log file, the number of recipes storable in the memory device, and/or the amount and/or content of support documentation available, etc. 
     At activity  7300 , project file elements can be written to the memory device responsive to the user input. The project file elements can be written beginning at a vacant memory segment. Alternatively, project file elements can overwrite a previously stored project file. 
       FIG. 8  is a flowchart of an exemplary embodiment of a method  8000  for using the memory cartridge. At activity  8100 , a first head marker, indicative of a beginning memory segment for a data log record to be written, can be located on the memory device. The data log record can be of a size storable on a single memory segment. Alternatively, the data log record can be of a size storable on a plurality of memory segments. Memory segments usable for data log storage can be spatially and/or logically contiguous, and/or can be writable sequentially. 
     At activity  8200 , the data log record, which can comprise a second head marker, can be written to at least the beginning memory segment. The data log record can be written on at least one vacant memory segment. Alternatively, the data log record can overwrite at least one memory segment used by an older data log record. The second head marker can contain information reflective of a location of a next memory segment for storage of a next data log record. In an exemplary embodiment, the data log file can be written in a logically circular buffer. The logically circular buffer can be characterized by data log records written to contiguous memory segments, the buffer commencing at a beginning memory segment. The logically circular buffer can be further characterized by the writing of the next data log record at the beginning of the buffer when the buffer is full. The next data log record can overwrite an oldest data log record written in the logically circular buffer. For example, if the buffer is full, the next data log record to be written can be written at the beginning of the buffer, thereby overwriting the data log record that was previously at the beginning of the buffer. The logically circular buffer can comprise a circular buffer wherein memory segments are physically contiguous to each other. 
     At activity  8300 , the first head marker can be changed to a record marker reflective of the data log record written in at least the beginning memory segment. The record marker, as changed, can be indicative of the successful writing of the data log record comprising the second head marker. 
     After activity  8200  and before fully completing activity  8300 , a power failure might occur. A power failure occurring before activity  8300  is fully completed can leave a data log file with two head markers turned on simultaneously. At activity  8400 , in an operative embodiment, the PLC can assure the presence of a single head marker after the power failure, via an error checking technique. The error checking technique can be an ones complement method, a Fletcher checksum method, a cyclic redundancy check method, and/or extended-precision checksum method, etc. The error checking technique, possibly coupled with knowledge of the position of the records in question and/or the position and/or direction that records are added to the memory device, can identify which record is the most recent, and thereby which head marker is erroneous. 
     In an operative embodiment, the PLC can disable and/or eliminate the older, duplicate head marker, or possibly convert the older, duplicate head marker to a non-head marker resulting in the presence of a single head marker in the data log file, that single head marker corresponding to the new record. Changing the value of a binary bit can disable the older, duplicate head marker. Alternatively, the PLC can inspect and test a marker, such as a time stamp marker, on each of the data log records, to determine the most recently written record. 
     At activity  8400 , the data log record can be read from the memory device. In an operative embodiment, the data log record can be read from at least one memory segment responsive to the data log structure. Information indicative of the data log structure can be stored separately in the memory device. 
     Still other embodiments will become readily apparent to those skilled in this art from reading the above-recited detailed description and drawings of certain exemplary embodiments. It should be understood that numerous variations, modifications, and additional embodiments are possible, and accordingly, all such variations, modifications, and embodiments are to be regarded as being within the spirit and scope of the appended claims. For example, regardless of the content of any portion (e.g., title, section, abstract, drawing figure, etc.) of this application, unless clearly specified to the contrary, there is no requirement for any particular described or illustrated activity or element, any particular sequence of such activities, or any particular interrelationship of such elements. Moreover, any activity can be repeated, any activity can be performed by multiple entities, and/or any element can be duplicated. Further, any activity or element can be excluded, the sequence of activities can vary, and/or the interrelationship of elements can vary. Accordingly, the descriptions and drawings are to be regarded as illustrative in nature, and not as restrictive.