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Non Volatile RAM (F-RAM & NVSRAM)

Nelson
New Contributor II

The MCU I use is stm32L476RG.

The test steps are as follows:

1. Put FRAM into hibernation mode,

2. Read the FRAM status register and read the value 0x00, indicating that FRAM has entered the hibernate state.

3. Put the MCU into hibernation mode,

4. Wake up MCU after 1 second,

4. Read the FRAM status register, and read the return value 0x40.

The problem is that I shouldn't be able to read the FRAM data at this point because it's still in hibernation mode and I haven't woken it up. I did not find that the CS PIN was pulled down for more than 4.5ms through the logic analyzer.

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Nelson
New Contributor II

Thank you for your help. After testing, I now understand that CS Line does not need to be pulled down for more than 4.5ms, but just give it a falling edge and then you can pull it up. I think the instructions in the data sheet for exiting hibernation mode are not very clear and can be confusing. Thank you again .

Nelson_0-1634893067597.png

 

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PradiptaB_11
Moderator
Moderator

Hi @Nelson ,

I am a little unclear after step 4. The device will come out of Hibernation when it sees a falling edge on CS pin. So i am unclear as to why you are trying to read the SR when the device is supposed to stay in Hibernation as per you. For reading SR you will have to first give a falling edge on CS which will push the device out of hibernation mode. 

CS line should have no falling edges on it until and unless you want the device to wake up.

 

Thanks,

Pradipta.

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Nelson
New Contributor II

Hi,Pradipta.

Thanks for your reply.

According to the chip manual, for FRAM to exit hibernation mode, CS Line needs to be kept low for approximately 4.5ms. When I read SR, the CS line obviously stayed down no more than 4.5ms, so I couldn't wake up FRAM. I didn't want to wake up the FRAM in the above test steps, but in step 5, I was able to read the value of SR. I don't know what the problem is. Note: I want to keep the FRAM hibernation while the MCU is in standby mode , so I keep the CS line at high level.

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Nelson
New Contributor II

Thank you for your help. After testing, I now understand that CS Line does not need to be pulled down for more than 4.5ms, but just give it a falling edge and then you can pull it up. I think the instructions in the data sheet for exiting hibernation mode are not very clear and can be confusing. Thank you again .

Nelson_0-1634893067597.png

 

View solution in original post

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