Abstract:
Battery backed memory for use in an industrial controller allows software disconnect of the battery and memory so that unplanned power outages may receive the benefit of battery backup, but battery power is not unduly wasted during planned power outages when data loss may be accommodated or other provisions may be made for saving data in nonvolatile memory.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       BACKGROUND OF THE INVENTION  
         [0001]    The invention relates generally to industrial control systems, and more specifically to an industrial control system having a battery backed solid-state memory, the battery preventing loss of data during momentary power interruptions.  
           [0002]    Industrial controllers are special purpose computers used for the control of industrial processes and the like. While executing a stored program, they read inputs from the controlled process and, according to the logic of a contained control program, provide outputs to the controlled process.  
           [0003]    Industrial controllers differ from regular computers both in that they provide “real-time” control (i.e., control in which control outputs are produced predictably and rapidly in response to given control inputs) and in that they provide for extremely reliable operation. In this latter regard, the volatile memory used by the industrial controller is often backed up with a battery so that data needed for the control program is not lost during momentary power outages. Volatile memory is that which requires power to maintain its stored data.  
           [0004]    Such “battery backed” memory, using a combination of static random access memory (SRAM) and a long life battery such as a lithium cell, is well known. In current control applications, synchronous dynamic random access memory (SDRAM) may be preferred to SRAM because of its higher density, faster speed, and lower cost. Unfortunately, the amount of power needed for SDRAM can be thirty times greater than that needed for conventional SRAM devices. The voltage requirements of SDRAM require that the lithium cell voltage be stabilized with a DC-to-DC converter, introducing additional power losses of about 25 percent. High speed SRAM is one alternative, but high-speed SRAM still draws about ten times as much current as the older SRAM devices, has much lower density than SDRAM in number of bits of storage per device, and costs much more than SDRAM per device.  
           [0005]    Many customers wish to disconnect power from their industrial controllers during the night, over weekends, and during scheduled factory shutdowns. The high power requirements of SDRAM and high speed SRAM produce unacceptable battery drain in these situations. At times, it may be desirable to ship an industrial controller preprogrammed from the factory. The one-month or more of transport time make battery back-up of the programmed data impractical.  
         BRIEF SUMMARY OF THE INVENTION  
         [0006]    The present invention allows automatic deactivation of the battery backup for periods of planned power outage. In this way, memory devices having high power consumption may be provided with battery back up during short periods of unexpected power loss, without risk of high battery discharge levels during longer scheduled shutdowns. The invention may include nonvolatile (e.g., Flash) memory into which selected data from the volatile memory may be saved prior to a planned shut down.  
           [0007]    Specifically, the present invention provides a battery backed memory system having a first line receiving a source of line voltage and a second line receiving a source of battery voltage to provide backup voltage when the line voltage is lost. A volatile solid-state memory receives voltage from the first line, and from the second line via an electronically controlled switch. A microprocessor communicating with the volatile solid-state memory and the electronically controlled switch, executes a program to open the electronically controlled switch in response to a signal indicating a planned cessation of line voltage.  
           [0008]    Thus it is an object of the invention to distinguish between and respond differently to power outages that are unexpected and that require battery backup and those which are planned in which battery backup may not be required.  
           [0009]    The system may further include nonvolatile solid state memory communicating with the microprocessor and the executed program may operate to transfer predetermined data from the volatile solid state memory to the nonvolatile solid state memory in response to the signal indicating a planned cessation of line voltage and prior to opening of the electronically controlled switch.  
           [0010]    Thus it is an object of the invention to allow storage of data in nonvolatile memory when a planned power outage is incurred, thus eliminating loss of critical data, and to allow for such a transfer while line voltage is present to ameliorate the power demands of programming common non-volatile memories.  
           [0011]    The invention may include a latch connected between the microprocessor and the electronically controlled switch so that the electronically controlled switch is latched open even after loss of power to the microprocessor.  
           [0012]    Thus it is another object of the invention to allow the microprocessor to be fully powered down during loss of line voltage without affecting the disconnection of the battery from the volatile memory.  
           [0013]    The invention may include circuitry for resetting the latch upon restoration of line voltage to the first line.  
           [0014]    Thus it is another object of the invention to ensure that battery backup is reestablished on next power up after an unplanned power outage without the necessity of resetting by the microprocessor.  
           [0015]    The volatile memory may include static and dynamic random access memory.  
           [0016]    Thus it is another object of the invention to provide a system that works not only with high current dynamic memories but also faster, higher current static memory systems.  
           [0017]    The system may include a DC-to-DC converter for use with the dynamic access memory and a voltage regulator for use with the static memory.  
           [0018]    Thus it is another object of the invention to provide improved battery backup operation for memory systems that include efficiency decreasing, regulation, or DC-to-DC conversions.  
           [0019]    The foregoing objects and advantages may not apply to all embodiments of the inventions and are not intended to define the scope of the invention, for which purpose claims are provided. In the following description, reference is made to the accompanying drawings, which form a part hereof, and in which there is shown by way of illustration, a preferred embodiment of the invention. Such embodiment also does not define the scope of the invention and reference must be made therefore to the claims for this purpose. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    [0020]FIG. 1 is a simplified perspective view in phantom showing a processor board within an industrial controller, the former which may include a battery backing up a volatile memory;  
         [0021]    [0021]FIG. 2 is a schematic representation of the present invention showing a microprocessor having an output communicating through a latch with a switch connected to disconnect battery backup from volatile memory during a planned power outage; and  
         [0022]    [0022]FIG. 3 is a timing diagram showing the signals at specific locations on the schematic of FIG. 2 during initial application of power to the industrial controller, an unanticipated power loss, and a planned shut down according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    Referring now to FIG. 1, an industrial controller  10  may include a chassis  12  incorporating a number of modules  14 ,  16 ,  18 , and  20  interconnected by means of backplane  22 .  
         [0024]    In particular, a power supply module  14  provides power from a line source  24  and regulates the power for distribution along the backplane  22  to the other modules  16 ,  18 , and  20 . A processor module  16  receives data along the backplane  22  from a network module  18  or an I/O module  20 . The network module  18  provides an interface with a communication network  34  such as EtherNet, or ControlNet to receive system control data or data from other I/O modules. The I/O module  20  provides an interface for input and output signals along I/O lines  27  communicating with the controlled process or machine. Generally, during operation of the industrial controller  10 , a program executed by the processor module  16  reads this input data to create output data that is then returned along the backplane  22  from a network module  18  or an I/O module  20 .  
         [0025]    The processor module  16  includes an internal processor circuit board  26  containing a battery  28 , volatile memory  30 , and processor circuitry  32 .  
         [0026]    Referring now to FIG. 2, the battery may be a lithium battery as is generally known in the art. Such batteries are not rechargeable and hence must be replaced when their power is exhausted. The volatile memory  30  may include static random access memory (RAM)  42  and synchronous dynamic random access memory (SDRAM)  44 , both of which require application of power to maintain their memory states. The processor circuitry  32  includes a microprocessor  36  communicating via an internal data and address bus  38  with the volatile memory  30  and nonvolatile memory  40  which together contain control data and the control program. The non-volatile memory may be so called “flash” memory well known in the art.  
         [0027]    According to methods well known in the art, the microprocessor  36  reads or writes to the volatile memory  30  or non-volatile memory  40  as is necessary to execute the control program. The microprocessor  36  may also communicate over bus  38 , or via a similar mechanism, with the backplane  22  and hence with I/O modules  20  or network module  18 .  
         [0028]    Referring still to FIG. 2, power for the SRAM  42  is received through a transistor  46 , which in turn receives power from a voltage regulator  48  of conventional design, connected to battery  28 . The regulator voltage is adjusted to the necessary voltage for the particular SRAM  42 . Generally voltage regulators operate to controllably reduce voltage. Similarly, power for the SDRAM  44  is received through a transistor  50  which in turn receives power from DC-to-DC converter  52  of conventional design, connected to battery  28 . Again, the DC-to-DC converter  52  is adjusted to the necessary voltage for the particular SDRAM  44 . The DC-to-DC converter operates to maintain the desired voltage to the memory with an input battery voltage above or below the desired voltage to the memory.  
         [0029]    The SRAM  42  and SDRAM  44  also have a connection to line power  56  obtained from the power supply module  14  through the backplane  22 . Thus, when line power  56  is available, no current need be or is drawn through transistors  46  and  50  preventing current drain on battery  28  and saving its capacity instead for periods of unexpected interruption of line power  56 .  
         [0030]    The non-volatile memory  40  is connected to line power  56 , as it does not require battery back up because it does not lose data when power is lost.  
         [0031]    The transistors  46  and  50  receive at their controlling inputs the output of an inverter  90  whose input is a signal (D) output from a latch  58 . In the example shown, the transistors  46  and  50  may be p-channel field effect transistors passing current from their drain to source upon application of a low state voltage at their gates. Thus, a high or set state of the output of the latch  58  will turn on transistors  46  and  50  allowing current flow to the SRAM  42  and SDRAM  44 , whereas a low or reset state of the output of the latch  58  will turn off transistors  46  and  50  preventing current flow to the SRAM  42  and SDRAM  44 . It will be understood that the particular voltage considered to be the “set” state is arbitrary and for the purposes of the claims herein, the terms “set” and “reset” should be construed to embrace either high or low voltages according to the necessary logic to be effected by the present invention.  
         [0032]    Latch  58  and inverter  90  may be powered directly from the battery  28 , bypassing transistors  46  and  50  so as to maintain their states even with loss of line power  56  or switching of the transistors  46  and  50 .  
         [0033]    The microprocessor  36  provides two output lines  66  and  68  which may be controlled by the program executed by the microprocessor  36 . Each output line  66  and  68  is received, respectively, by one inverter  70  and  72 . The output of inverter  70  is received by a first input of a dual input AND gate  64 .  
         [0034]    Associated with the microprocessor  36  of the processor circuitry  32  is reset timing circuitry  60  receiving line power  56  to provide a series of reset signals  62  needed to properly initialize the microprocessor  36  and other circuitry when power is first applied to the processor circuitry  32 . Such circuitry is well known in the art. The reset signal  62  of the reset timing circuitry  60  rises shortly after power is first applied to the processor circuitry  32  and is received by the second input of the dual input AND gate  64 .  
         [0035]    The output of the dual input AND gate  64  is received by the clock input of a standard D-type latch  58  whereas the output of inverter  72  is received by the data input of the latch  58 . Thus generally, control of the latch  58  is provided by the reset signal  62  and the two output lines  66  and  68 .  
         [0036]    Referring now to FIG. 3, at a time prior to the application of line power  56  to the processor circuitry  32 , indicated by interval  76 , reset signal  62  indicated as waveform (C), output line  66  indicated as waveform (A) and, output line  68  indicated as waveform (B) will all be low. Upon application of line power  56 , indicated by a vertical dotted line  78 , power to the volatile memory  30  (shown in FIG. 3) will rise indicated by waveform (P) to a predetermined normal voltage necessary for supplying power to the non-volatile memory  40 , the microprocessor  36 , and the reset timing circuitry  60 . Whereas a single power level is indicated, more generally different voltages will be provided by power supply module  14  to the various devices of SRAM  42  and SDRAM  44 .  
         [0037]    At a predetermined interval  80  after the application of power, a rising edge of reset signal  62  (waveform (C)) will occur. Insofar as microprocessor output lines  66  and  68  remain low during normal start-up of the microprocessor, the output of the AND gate  64  will provide a rising edge clocking the latch  58  while a high value will be applied to latch input D from inverter  72 .  
         [0038]    The result is a high or set latch output which, through the operation of transistors  46  and  50 , will connect the SRAM  42  and the SDRAM  44  to battery power from battery  28  as has been described above in addition to their connection to line power  56 . Line power  56  may be attached to SRAM  42  and SDRAM  44  in a manner so as to inhibit power being drained from the battery so long as line power  56  is present. For example, this may be done by back biasing a diode junction or the like.  
         [0039]    Referring again to FIG. 3, after this time, a power interruption  82  causing a loss of line power  56  will cause power from battery  28  to be conducted by transistors  46  and  50  through to the SRAM  42  and SDRAM  44  preventing loss of data on these devices. After this time, as indicated by vertical dotted line  84 , a planned shutdown signal may be received by the microprocessor  36 . The planned shutdown signal may, for example, be received as a dedicated input from a front panel control (not shown) or received through bus  38  on the industrial controller (and thus from the network  34  or an I/O line  27  or as a software command implemented as a portion of the controlled program executed by the microprocessor. The planned shutdown signal, as the name implies, indicates that a planned interruption of line power  56  will occur.  
         [0040]    At this time, during a data storage interval  86 , the microprocessor  36  may cause a transfer of predetermined data from SRAM  42  and SDRAM  44  to the non-volatile memory  40  using the available line power  56  to implement the writing to the non-volatile memory  40 . The predetermined data is that selected by the programmer based on the particular application of the industrial controller, but may include programs and program data values and or I/O values.  
         [0041]    At the conclusion of the data storage interval  86 , the microprocessor  36  may change output line  68  and may pulse output line  66  to cause the output of the latch  58  (signal (D)) to be reset at vertical line  88  turning off transistors  46  and  50 . In this way, when line power  56  is lost, unlike during interruption  82 , there is no drain on battery  28 .  
         [0042]    The latch  58  is connected directly to the battery  28  and so remains powered during the turning off of transistors  46  and  50 . The relatively low power requirements of the latch  58  do not cause a significant drain on the battery  28 . With the latch  58  holding the transistors  46  and  50  off, power may be cut to the microprocessor  36  with or without transistors  46  and  50  turning on again. Thus the circuit allows current drain on the battery  28  to be minimized.  
         [0043]    Generally, the planned shutdown signal precedes a controlled shut down of the industrial controller  10 , for example, in evenings or at night so as to save power or may be powering down prior to shipping of the industrial controller  10  to a customer with critical data stored in the non-volatile memory  40 . By eliminating the drain of the volatile memory  30  on the battery  28 , battery life can be increased dramatically, typically from one week to one year or more. It will be understood, however, that all current drain on the battery is not necessarily prohibited. For example, a real-time clock may also be connected to the battery  28  on a permanent basis.  
         [0044]    It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but that modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments also be included as come within the scope of the following claims.