SEMPER™ NOR flash supports two ECC configurations - SECDED (1-bit error correction and 2-bit error detection) and SECSED (1-bit error correction and 1-bit error detection). SECDED is the default mode. In this configuration, the 16-byte ECC unit data requires a 9-bit ECC for 2-bit error detection.
When SECDED is enabled, byte-programming, bit-walking, or multiple program operations to the same data unit (without an erase), even with the same data pattern are not allowed, and will result in a program error.
When changing the ECC mode, the host should first erase all sectors in the device. If the ECC mode is changed without erasing the programmed data, subsequent read operations may not be protected by ECC (see Section 4.1 “Error Detection and Correction” of the datasheet). This occurs because SECDED mode uses the 9th ECC data bit as well, which is assigned as the ‘ECC disabled’ bit in SECSED mode. If ECC mode is changed without erase, the current ECC unit's status may be ‘ECC disabled’ or ‘incorrect ECC data’ according to the 9th ECC data bit status. In these cases, the read operation shows the raw data without ECC correction.
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