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Electronics => Repair => Topic started by: klaus11 on October 23, 2016, 06:55:33 pm

Title: NVRAM new but with data!, it's possible? (Mouser)
Post by: klaus11 on October 23, 2016, 06:55:33 pm

I placed an order to Mouser, including NVRAM DS1220AD. My Surprise is that is dated 2014 and has written data.
My question is a new NVRAM, or Mouser me scammed.
I've never bought NVRAMS new only ebay, so I wonder.

Opinions are welcome.

Title: Re: NVRAM new but with data!, it's possible?
Post by: ataradov on October 23, 2016, 07:03:29 pm

What kind of data? I would assume that devices are tested before leaving the factory, so if it looks like test patterns, then I think it is fine.

Also, SRAM is "initialized" to random values at power up, so when they assemble this, original content of the RAM will be random noise. If they don't explicitly erase it to some known value, then you get that random noise.

And I don't see any notes on the original contents in the datasheet, so it can be anything,

Title: Re: NVRAM new but with data!, it's possible? (Mouser)
Post by: wn1fju on October 23, 2016, 07:31:19 pm

I just received a DS1225AD from Mouser a couple of days ago.  Mine had a 2016 date code and also had "data" when I read it.  Nothing to worry about.

Title: Re: NVRAM new but with data!, it's possible? (Mouser)
Post by: SeanB on October 23, 2016, 07:33:45 pm

RAM chips will always power on to some state, not all zero or one ( that is the default for EPROM and EEPROM, as they are erased during manufacture as part of the testing for QC), and the actual state of each cell will vary, though you will get blocks that power on to a particular value or just random values.

The NVRAM chips as manufactured have a non resettable freshness bit in there, that is set to power off the internal RAM until the first power up of the unit in use, which then enables the on board supply to the memory, and this is then only reset when the battery is totally flat again. This is to give the best storage life, as then the minute drain from the RAM chip is not applied to the coin cell there.

If it has valid data ( readable strings of data in locations, increasing numbers in a sequence) then it probably was a chip that had full QC done on it in test, or a return, though if it was still in the original unopened pack it would be hard to see if it was a return.

Title: Re: NVRAM new but with data!, it's possible? (Mouser)
Post by: klaus11 on October 23, 2016, 07:42:41 pm

(https://c3.staticflickr.com/6/5696/29888737594_2f5b7d3141_z.jpg) (https://flic.kr/p/MxaAnY)Captura NVRAM (https://flic.kr/p/MxaAnY) by  (https://www.flickr.com/photos/68937774@N04/)

Title: Re: NVRAM new but with data!, it's possible? (Mouser)
Post by: ataradov on October 23, 2016, 07:45:15 pm

That looks pretty random, normal for SRAM.

BTW, SRAM in the microcontrollers will have similar "data" on power up.