• Dealing with Permanent Software Write Protection and SPD EEPROM devices incorporating the PSWP feature.

Permanent Software Write Protection (PSWP) is a non-reversible protection for the first 128 bytes of the data array of EEPROM that can be set permanently by the software. The second half of the data array keeps to be available for write operations. The difference between the hardware and software write protection is that the first one uses the WP pin of the EEPROM device to protect the entire data array. Besides, once PSWP has been enabled it cannot be reversed while the hardware write protection can be disabled by tying the WP pin to Vss (Ground).

However, not all EEPROM devices incorporate PSWP. The most common marking of the EEPROM device with a PSWP feature is 3402. The number 34 stands for EEPROM device for IIC (Inter-Integrated Circuit) bus with Permanent (or Reversible) Software Write Protection feature. It is a next generation of EEPROM devices for SDRAM modules designed as a replacement for the widely used legacy 24C02 series chip that do not incorporate PSWP. The 3402 chip in TSSOP8 package found to be used with DDR and DDR2 SDRAM widely. Anyway, 3402 chips can be found even on older PC SDRAM modules.

Today the most popular EEPROM device with the PSWP feature is the M34C02 2Kbit EEPROM being produced by STMicroelectronics. This device is employed by many DRAM vendors such as Crucial, Kingston, Samsung, etc. There are many analogs of this from other vendors like ATMEL AT34C02C, ISSI IS34C02B, ON Semi (formerly known as Catalyst Semiconductor) CAT34C02, Microchip 34LC02 and others. But all of them provide the same technique for enabling PSWP to protect the first half of EEPROM data content.

ON Semiconductor CAT34C02 EEPROM
with the PSWP feature
Microchip 24LCS52 EEPROM
The full clone of the 34C02 chip

To identify EEPROM devices manufacturers apply its part numbering system. But since the EEPROM device is a very small chip, manufacturers use an abbreviation of part numbers which is shorter than a full part number. As we mentioned above, 3402 is the most common part number code. Also, we can find part number codes on the top side of the chip package like 34C1, 302RP, AT34, etc relative to the 3402 EEPROM device. But in most cases it is difficult to determine a vendor of the EEPROM device if EEPROM's part number on the package is missing. The following table combines EEPROM chips compatible with the 3402 chip incorporating the PSWP feature.

Manufacturer EEPROM Device
FW32 Firchild Semicond. FM34W02ULMT8
F32L Firchild Semicond. NM34C02LMT8
34V2 Microchip 34VL02
34A2 Microchip 34AA02
34L2 Microchip 34LC02
05AB Microchip MCP9843
243B Microchip MCP9243
3402 STMicroelectronics ST M34C02
3402W STMicroelectronics ST M34C02-W
302RP STMicroelectronics ST M34C02-R
E02FR STMicroelectronics ST M34E02

Anyway, there are SWP-featured serial EEPROMs with a part number that starts with "24". For instance, Samsung Semiconductor used to employ the Microchip 24LCS52 serial EEPROM for DDR3 SDRAM unbuffered DIMMs. The next table groups EEPROM devices with a marking code starting with "24".

TSSOP8 PN Code Manufacturer EEPROM Device
A52 Microchip 24AA52
S52 Microchip 24LCS52

Beginning from version Thaiphoon Burner is capable of determining PSWP feature in the EEPROM device. To check whether PSWP is incorporated select PSW Protection from the EEPROM main menu. Now look at the checkboxes. They should not be grayed out if corresponding SPD EEPROMs are not write-protected. Otherwise your SPD EEPROMs are hardware or software protected from being rewritten or they are not relative to the 3402 chip.

SPD EEPROM at SMBus address 52h is not write-protected.
SPD EEPROMs at other addresses are write-protected or do not incorporate PSWP feature.

Since version Thaiphoon Burner can identify SPD EEPROM chips incorporating a temperature sensor. This combination SPD device can be found on DDR3 SDRAM modules only.

Related Articles:

О защите от перезаписи микросхемы SPD EEPROM.

datasheets on EEPROM devices mentioned above

ATMEL AT34C02C (Revision E, 03/2011)
ISSI IS34C02B (Revision 00E, 09/2009)
Microchip 24AA52/24LCS52 (12/2005)
Microchip 34AA02/34LC02 (Revision E, 01/2010)
Microchip 34VL02 (03/2008)
ON Semi CAT34C02 (Revision 14, 12/2009)
ST M34C02-R (Revision 11, 03/2009)
ST M34E02 (Revision 11, 05/2011)

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