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Microcomputer having an error-correcting function based on a detected parity error

  • US 5,404,495 A
  • Filed: 11/07/1991
  • Issued: 04/04/1995
  • Est. Priority Date: 11/20/1990
  • Status: Expired due to Fees
First Claim
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1. A microcomputer comprising:

  • a data SRAM for storing data and outputting stored data;

    a parity SRAM, coupled to the data SRAM for storing a parity associated with each of the data stored in the data SRAM and for outputting the stored parity;

    a total-sum storage, coupled to the data SRAM, for storing a total sum of data associated with a block of stored data in the SRAM and for outputting the stored total sum of data; and

    a CPU for controlling the data SRAM, the parity SRAM and the total-sum storage, the CPU providinga summing function for calculating the total-sum of data associated with the block of stored data;

    a total-sum changing function for calculating a new total sum of data Snew associated with the block of stored data when new data Xnew is stored in the block of stored data, the new total sum of data Snew being based on an equation
    
    
    space="preserve" listing-type="equation">S.sub.new =S.sub.old +X.sub.new -X.sub.old,where, Xnew denotes new data after new data has been stored, the block of stored data replacing old data Xold, andSold denotes an old total sum of data associated with the block of stored data before the new data is stored in the block of stored data;

    a parity adding function for calculating a vertical parity associated with the new data when the new data is stored in the data SRAM and for storing the vertical parity in the parity SRAM;

    a parity error detecting function for detecting an error in the vertical parity of data associated with the old data Xold output from the parity SRAM when the old data Xold is output from the data SRAM, and for producing an error indication when an error is detected in the output vertical parity; and

    an error correction function for calculating and correcting data stored at the address where the error has been detected by subtracting data stored at all addresses of the block of stored data other than the data stored at the address where the error has been detected from the new total sum of data Snew associated with the block of stored data.

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