I2C EEPROM recommendation (with software write protect to prevent corruption)

Hi,

I'm designing a datalogger which contains (among other things) a PIC and an I2C EEPROM.

I need some advice regarding the I2C EEPROM I should use.

I am trying to ensure that during the course of normal operation (i.e. no matter what happens to the power supply voltage during power-up/down) the EEPROM contents will not be corrupted.

The PIC runs off a regulated 5V supply and has power fail detect circuitry so that it can detect when the regulator input voltage drops below normal levels so it can write crucial data to EEPROM before 5V drops below valid levels (I should have enough time to do this). I plan to enable brownout detect for the PIC so it'll go into reset at about 4V.

As for the EEPROM choice I was planning on using a 24C01C (Microchip) because:

it supports page write (16 byte buffer) so I can quickly write data when power fails it has a fast write cycle time (1mS for either per byte or page write) it is rated for 4.5V - 5.5V operation and disables writes when Vcc falls below about 3.8V or so. it comes in a DIP package (yeah, yeah, SOICs are more common but my glasses are already thick enough ;) Digikey has it

The 24C01 is 128x8 (1Kbit), which is enough for my app. Both the PIC & 24C01C EEPROM reset at approx the same levels (approx

4V). I was thinking at this point that things should be pretty reliable.

But then I read

which suggests that for greater reliability against corruption I should use an EEPROM that features software write lock. To quote: "Using software write-locked memories greatly enhances system-data integrity. A software write-locked memory requires a special sequence of writes and reads to occur before the part allows any write requests to proceed. Another sequence should be available in the device to lock the part after writing is complete. The longer and more unusual the unlock sequence, the better the part is protected. Software write protection is much more effective if the memory is automatically forced back into the locked state at some time before system power down, leaving the memory contents secure during both the power up and power down intervals"

My questions:

1. For my present design (described above) is using the 24C01C (which doesn't have the software write protection) likely to be reliable?

1. Can someone suggest an I2C EEPROM (prefer DIP) that has the software write lock function? I have tried looking at both microchip and atmel's sites but their parametric searches didn't mention this function. I know some 25xxx SPI EEPROMS have the lock function but I'm kinda low on spare I/O pins and would prefer to stick with 2 wire I2C. (I don't need a huge storage space, 128x8 or 256x8 probably will be ok unless I resort to software error correction or something).

2. I realise there are error correcting codes and other software techniques that I could use to detect/recover if data has been corrupted. Are there any simple (i.e. in terms of code size and execution speed) suggestions that have worked well for anyone?

1. Yes, I know I could use FRAM here - but unfortunately no longer available in DIPs ;) (I want to try to solve this using EEPROMs anyway).

Thanks for your advice Kevin.

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