Protection circuit for storage of volatile data

[73] [21] [221

[5 1] [521 [531

[56]

VOLATILE

Inventors:

Assignee:
Appl. No.:
Filed:

Int. Cl.3 .... ..

DATA

Thomas K. Hiniker, Mankato; Vincent N. Bush, Madison Lake, both of Minn.

Field of Search .............. .. 365/226, 227, 228, 229

Attorney, Agent, or Firm—-Merchant, Gould, Smith, Edell, Welter & Schmidt

151] ABSTRACT

A protected memory circuit for use with an electronic data system includes a memory element such as a shift register, and memory control or lock means to selectively control enablement of the memory element for read/ write operations. A separate power supply which may be a charged capacitor is used to power the memory and memory lock circuits in case of a power interruption in the main system with which the memory is being used, so that volatile data can be stored for re-use by the main system after the main power is restored. The lock includes a counter and a gate for inhibiting clock pulses to the memory element until a predetermined number of control pulses have been received to initiate a read/write operation. At all other times the clock input is blocked or clamped to prevent spurious signals or power surge transients from altering the stored data.

10 Claims, 3 Drawing Figures

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‘_ PROTECT ION CIRCUIT FOR STORAGE OF . . _ I » VOLATILEDATA

TECHNICAL FIELD OF THE INVENTION

The invention pertains to the field of electronic systems for data processing, handling, monitoring and calculation. More specifically, the invention pertains to an improved memory circuit having a locking circuit especially well adapted for use in connection with an electronic data system, for storage of volatile data associated therewith. K - i ' ’

BACKGROUND OF THE PRIOR ART _ i

Digital electronic systems have been applied to a great number of fields,-for performing a wide variety of functions including monitoring, control and testing, and the processing, transmitting, receiving and handling of data; In many applications of digital systems, memory circuits are used for the storage of digital data, either on a short term or long term basis. One particular application for -memories, to which the present invention is especially adapted, is the use of a temporary memory for the storageof volatile data. An example of this type of application is in association with a computer, wherein certain data and programs are stored in more or less permanent form, for example magnetic tape, but certain otherdata is stored for a short term in the electronic memory within the computer. This memory is said to be volatile, in thesense that in the case of a power interrup

tion to the computer, the data previously stored in elec-,

tronic memory would be lost. Recognizing the need for a way to preserve this volatile data in the event of a power interruption in order to avoid loss of data and the resulting disruption and complication in start-up procedure, the prior art has provided means for storing important volatile data in the event of such an interruption. In large digital computers, circuits are often provided for sensing an impeding loss of power supply, and for interrupting the-normal program to save the contents of the volatile memory by transferring it quickly to a separatejmemory, orto magnetic memory in -a brief instant before the loss disables the computer. »

T A similar need for storage of volatile data exists with respect to smaller computer systems, for example microprocessor systems, but cost consideration for user devices employingsmaller computers or microproces

sors often prevents use of the volatile memory storage techniques employed in larger computers. An example would be in a monitoring or control device employing a microprocessor. Typically, the program for the microprocessor, together with certain numerical constants or .values employed in calculation in its program, are stored in some type of read only memory (ROM). The ROM is not affected by any interruption of power to the microprocessor, so the bulk of the program and important data is already in non-volatile memory. However, typically the microprocessor system receives certain operating data from sensors, for example, which data is to be counted, stored, displayed, or used in calculations, depending upon the intended use for the device. Such data is commonly stored in random access memory (RAM) "within the microprocessor, and this type of electronic RAM memory is lost upon interruption of power to -the microprocessor circuits- Such a power interruption might occur unexpectedly due to a failure somewhere in the source of power for the device, or it may occur intentionally as where the device is turned

2 off for a period of time with the intention of resuming the same monitoring, calculations, process, etc. later using data previously developed. ~

With the development of complementary metal oxide

semiconductor (CMOS) devices which are noted for their very low power drain, it has become common to provide an auxiliary CMOS‘memory for storage of data for a microprocessor, and the CMOS memory device can be powered from a separate smallbattery, or even from a large capacitor normally charged from the power supply but operative to supply energizing current to the CMOS memory for a certain period of time following removal of the main power supply. Although these techniques are generally successful, a problem still remains in that part of the data can be lost, or spurious data can beinserted in the memory due to voltage spikes or other transients occurring during shut-down or start-up. of the mircoprocessor and associated components during and following a power failure. Also, in the case of a system operating on a vehicle such as a tractor, automobile, boat, airplane, etc. power is generally received from the'vehicle’s battery and generator or alternator, and these sources are notoriously noisy with interference and spurious signals that can interfere with the intended operation ofithe-memory for the volatile data.~ ' . * - ‘ " _ .

SUMMARY OF THE INVENTION '

The present invention provides‘ a protected memory circuit for use with an electronic data system, especially adapted for storage of volatile data and rejecting spurious signals that might accompany a power interruption, for example. The invention includes a memory for storage of the electronic data, including input and output means for connection to the electronic data system for transfer of data therebetween. Means are provided in association with the memory for selectively inhibiting or enabling the memory with respect to the input, or the output of data. Memory control means are provided in conjunction to the inhibiting and enabling means of the memory, the control means being adapted to receive ‘control pulses from the electronic data system with which the memory is being used. The control means normallyinhibit the memory, but upon receiving a predetermined number of control pulses the control means enables the memory means for the input or output of data. ‘ ' K '

According to a preferred embodiment of the invention, a shift register is used for the memory means, with data being serially loaded in the shift register for storage. In this embodiment the memory control means includes a lock having a counter for registering the number of controlpulses received, and gating means connected to control application of clock signals to the shift register. In this manner the memory can be inhibited from accepting and shifting data by preventing the clock signals from enabling the shift register.