EEPROM with embedded ECCx4 feature

AN2440

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Doc ID 023074 Rev 4

2.2

Read operation with word management

Besides the additional ECC bits in the memory array, the EEPROM has an additional logic

block able to compute the ECCx4 signature, and to detect and correct possible bit errors in

the data word.

As the ECC signature (6 ECC bits) is a function of the 4 data bytes in the word, the word is

always considered as the smallest entity in the read process of the EEPROM. Figure 6

explains how the read process is managed.

Figure 6.

Read process of an EEPROM with embedded ECCx4

The steps of the read process illustrated in Figure 6 are described below:

1.

The user requests a read of three bytes: byte 1, byte 2 and byte 3.

2.

Internally, the entire word is read (4 data bytes and 6 ECC bits) and stored in a RAM

buffer.

3.

A new ECC signature is computed from the 4 data bytes read from the memory.

4.

The new ECC signature is compared to the ECC bits read from the memory. A

difference indicates that there is an error, the bit error is detected and corrected after

further calculations.

5.

The RAM buffer now contains byte 0, byte 1, byte 2 and byte 3 (byte 3 corrected) and

the read ECC bits.

6.

The data is shifted out of the memory with the Most Significant Byte first; that is, byte 1

followed by byte 2 and byte 3.

Byte0

ai13476

Byte1 Byte2 Byte3

ECC

Byte0 Byte1 Byte2 Byte3

ECC

Memory array

38 read bits stored into RAM buffer

Compute

ECC signature

Comparing new ECC bits with the read ECC bits

Byte0 Byte1 Byte2 Byte3

ECC

I/O Shift Register

Byte1, byte 2 and byte 3 are shifted out serially, MSB first

Step 1

Step 2

Step 3

Step 4

Step 5

Step 6

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Sensing block

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