Reliable backup memory

• US 5,745,425 A
• Filed: 08/29/1996
• Issued: 04/28/1998
• Est. Priority Date: 08/29/1996
• Status: Expired due to Term

• Current Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Anderson, Dennis Lee, Jacks, Steven Anthony
• Primary Examiner(s): YOO, DO H
• Application Number:
  US08/703,143
• Time in Patent Office: 607 Days
• Field of Search: 365/226, 365/201, 365/185.22, 365/185.04, 365/185.09
• US Class Current: 365/226
• CPC Class Codes: G06F 11/1433 during software upgrading
• CPC Class Codes: G11C 16/102 External programming circuits, e.g. EPROM programmers; In-circuit programming or reprogramming; EPROM emulators
• CPC Class Codes: G11C 16/22 Safety or protection circuits preventing unauthorised or accidental access to memory cells

Abstract

An Electrically Erasable Programmable Read Only Memory (EEPROM) provides backup and initialization data for random access memory (RAM) in a control unit. In order to update the EEPROM with new releases of a program and data, the EEPROM is divided into two segments, each with a separately controllable write enable voltage. Advantageously, this allows a new release to be written into one segment of a single EEPROM without erasing the other segment until the newly written segment has been verified.

Claims

1. A method of providing reliable backup memory from an electrically erasable programmable read only memory (EEPROM), having a higher voltage power supply that must be connected to the EEPROM in order to change its contents, comprising the steps of:

removing said higher voltage power supply when the EEPROM is not being updated;

applying said higher voltage power supply only when said EEPROM is being updated;

splitting said EEPROM into at least two segments, each segment being fed by a separately controllable source of said higher voltage; and

updating one of said segments while retaining a previous version of the information stored in said EEPROM in the other segment while supplying the higher voltage only to the one segment being updated.

2. The method of claim 1 further comprising the steps of:

following a successful updating of the one segment of said EEPROM, removing the higher voltage from the successfully updated segment;

applying the higher voltage to the other segment; and

clearing the other segment.

3. A method of providing reliable backup memory from an electrically erasable programmable read only memory (EEPROM), having a higher voltage power supply that must be connected to the EEPROM in order to change its contents, comprising the steps of:

removing said higher voltage power supply when the EEPROM is not being updated;

applying said higher voltage power supply only when said EEPROM is being updated;

initially receiving said EEPROM with all devices cleared prior to putting said EEPROM into service;

testing whether said EEPROM is cleared;

if said EEPROM is not cleared, avoiding testing devices of said EEPROM;

whereby excessive tests of devices of said EEPROM are avoided.