Method and apparatus for a backup power controller for volatile random access memory

• US 5,204,963 A
• Filed: 12/07/1990
• Issued: 04/20/1993
• Est. Priority Date: 12/07/1990
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Digital Equipment Corporation (HP Inc.)
• Inventors: Arnott, Randy M., Noya, Eric S.
• Primary Examiner(s): RICHARDSON, ROBERT
• Application Number:
  US07/626,586
• Time in Patent Office: 865 Days
• Field of Search: 364/273.4, 364/948.5, 371/14, 371/66, 365/228, 365/229, 395/750
• US Class Current: 365/229
• CPC Class Codes: G06F 1/30 Means for acting in the event of power-supply failure or interruption, e.g. power-supply fluctuations for resetting only G06F1/24
• CPC Class Codes: G06F 11/2015 Redundant power supplies power supply failure G06F1/30

Abstract

A method and apparatus for a software actuable backup power controller for selectively controlling power to a volatile random access cache memory. If memory does not contain any data that needs to be retained during a primary power failure the controller isolates memory from the backup power supply during the power failure. Only when the memory contains data to be retained during a power failure will memory be treated as non-volatile and is the backup power supply connected to memory on primary power failure. By selectively enabling the backup power supply with software commands from the computer, a suitable cache memory can be constructed with a compact non-rechargeable battery.

Claims

1. Apparatus for providing power to a volatile random access memory in a computer system comprising:

a circuit board;

volatile random access memory mounted on said circuit board;

a primary power source normally connected to said memory;

a backup power source mounted on said circuit board normally disconnected from said memory;

first means mounted on said circuit board, said first means connected to the computer system, responsive to a command from the computer, for enabling said backup power source in the event that said memory stores data that must be preserved;

second means mounted on said circuit board, said second means connected to said primary power source, for sensing failure in said primary power source; and

coupling means, mounted on said circuit board, said coupling means connected to said first and second means, responsive to said first means on enablement and to said second means on sensing of a failure in said primary power source for disabling said primary power source and connecting said backup power source to said memory for enabling preservation of data in said memory on primary power source failure.

2. The apparatus according to claim 1 wherein said first means includes a shift register for receiving a predetermined coded command from the computer system for selectively enabling said backup power source.

3. The apparatus according to claim 2 wherein said second means includes power sensing logic for monitoring the status of said primary power source.

4. The apparatus as in claim 3 wherein said backup power source is a battery and said sensing means also monitors the condition of said battery.

5. The apparatus according to claim 4 further including means for providing to the computer information on the condition of said battery.

6. The apparatus according to claim 4 wherein said battery in a non-rechargeable battery.

7. The apparatus according to claim 1 wherein said backup power source is a battery.

8. The apparatus according to claim 1 wherein said coupling means includes a semiconductor power switching device.

9. The apparatus according to claim 1 wherein said backup power source is a non-rechargeable battery and wherein said first means, said second means, and said coupling means, said battery and said memory are formed as an integrated semiconductor package.

10. A controller in a computer system for enabling selective coupling of one of a first and second sources of power to a volatile random access memory comprising:

a circuit board having the memory mounted thereon;

a first power source connected to the memory;

a second power source mounted on said circuit board;

sensing means, mounted on said circuit board, said sensing means connected to said first power source, for detecting failures in said first power source;

means, mounted on said circuit board responsive to the computer system for providing a first signal indicative of a determination that data stored in the memory are to be preserved and a second signal indicative of a determination that said data stored in the memory are not to be preserved; and

coupling means, mounted on said circuit board, said coupling means connected to said sensing means and to said signaling means, responsive to said first and second signals and the detection of a failure of said first power source by said sensing means, for respectively enabling connection on said first signal or disabling connection on said second signal of said second power source to the memory on failure of said first power source.

11. The controller according to claim 10 wherein said second power source is a non-rechargeable battery.

12. The controller according to claim 10 wherein said means responsive to the computer system includes a register for receiving a predetermined command from said computer system and an AND gate for providing said first signal on receipt thereof.

13. The controller according to claim 12 wherein said sensing means provides a second input to said AND gate on detection of failure in said first power source and said coupling means is responsive to the output of said AND gate.

14. A method for powering a volatile random access memory capable of retaining data comprising:

supplying primary power to a volatile random access memory mounted on a circuit board;

sensing the condition of said primary power for failures;

determining if the data in said memory should be retained when failures are sensed in said primary power; and

upon sensing of a failure condition, disabling said supplying of primary power to said memory, and connecting a backup power source to said memory, said back up power source mounted on said circuit board when said step of determining determines that the data should be retained or isolating said backup power if the step of determining determines that the data in said memory should not be retained.

15. Apparatus for supplying power to a volatile random access memory storing data comprising:

means for sensing if the data should be preserved;

means for sensing a primary power failure; and

means, responsive to a determination if the data should be preserved and a failure of said primary power, for switching to a backup power.

16. The apparatus as in claim 15 further including register mans for receiving a predetermined coded command indicating if the data should be preserved.