Ram data not init after power off for seconds

[floodever]

Posted on June 08, 2009 at 13:27

Ram data not init after power off for seconds

[floodever]

Posted on May 17, 2011 at 15:03

Dear all,

I'm now working on stm8af51bb macro chip.According to user manual,wo could keep data in a special RAM area and left the data uninitialized after a chip reset. Truely we've realized this function.

But now comes up another problem: Once chip is normally working, a sudden low power pulse occurs----I mean chip may lose power supply for seconds,then how could I keep the data in a specific RAM area uninitialized? Need a special circuit support to realize this function?

Thx for all.

[alexanderczajor9]

Posted on May 17, 2011 at 15:03

Hello floodever,

from your description, the problem is not very clear. I guess that you mean the following:

- the RAM shall keep the data you have written previously, even if the supply voltage is going down.

Is this correct ?

If yes, then you need to consider that keeping the RAM content cannot be guaranteed below 2.6V. It is undefined what happens to the RAM below this voltage.

In order to keep data over a voltage brown out, you need to

- either ensure that the VDD of the micro does not drop below 2.6V during this time

- or use the internal NVM (data EEPROM) to store the data. It then is important how frequently you update the concerned data in the RAM.

• If it is updated rarely (let's say up to 100k time during the life of the application), then you can store the concerned data directly in EEPROM

• If it is updated more frequently, you need to follow another strategy: Monitor the supply voltage and if the voltage drops below the nominal one, you need to write the concerned data to the EEPROM before the voltage falls below the minimum operating voltage of 3.0V. Of course this strategy needs correct dimensioning of the filter capacitors and low power strategy.
  OK before going more in depth, let us know more details.
  Have a good day
  Alexander
  [ This message was edited by: alexanderc on 04-06-2009 09:48 ]

[floodever]

Posted on May 17, 2011 at 15:03

Dear alexanderc,

Great thanks for your detailed reply.

Nowadays I'm busy on IAP program,so the issue was postponed to deal with.I'll do some test based on your last reply and then send you more details.

By the way,our system power supply is 3.3v(VDD),so is the threshold voltage for keeping RAM data still 2.6v? I'm sorry that we didn't have detailed electrical characteristics on this micro chip(STM8AF51BB,100pin,256KBytes flash).

Thansk & Best regards.