Browse Prior Art Database

Write Protection Circuit for FLASH Memory

IP.com Disclosure Number: IPCOM000118397D
Original Publication Date: 1997-Jan-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 4 page(s) / 78K

Publishing Venue

IBM

Related People

Benayoun, A: AUTHOR [+3]

Abstract

Most of the Read Only Storage (ROS) are now replaced by FLASH memories. The code is downloaded in the FLASH memory by the microprocessor at power-on. This invention inhibits a write operation to the FLASH memory after it is programmed.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 53% of the total text.

Write Protection Circuit for FLASH Memory

      Most of the Read Only Storage (ROS) are now replaced by FLASH
memories.  The code is downloaded in the FLASH memory by the
microprocessor at power-on.  This invention inhibits a write
operation to the FLASH memory after it is programmed.

      The advantage of the current solution is to protect the code
like a ROS.

      The invention may be applied to any electronic design based on
a ROS replaced by a FLASH memory.

The idea is to insert a control logic on the FLASH memory write
signal input as follows:

                            (Image Omitted)

From a software standpoint, the FLASH memory is organized as follows:

                            (Image Omitted)

Remarks:
  o  The loader is built-in by the manufacturing site
  o  Most of the time, the FLASH memory is not fully occupied
      and, therefore, there is a Not_Used area

Mode of operation:
  o  After power-on, the microprocessor jumps to the
      Start_Address, reads the loader code and executes it.  This
      bootstrap downloads the operational code from the main
      memory into the FLASH memory.
  o  When the code is loaded, the microprocessor has to perform
      a write operation at the FLASH End_Address location.
  o  The control logic detects these different phases and performs
      the following functions:
     1.  Inhibits the write signal to the FLASH memory after a
          power-on reset
     2.  Detects the microprocessor read Start_Address op...