RAM Retention in SYSTEM OFF seems to work although not enabled

[Mathias Mitterdorfer]

I tried this using the ram_retention example from the SDK (nRF5_SDK_15.3.0).
The example (Ram Retention) still seems to work if the lines concerning NRF_POWER->RAMON and NRF_POWER->RAM[0].POWERSET are commented out. 

Can somebody please comment on this.

Thanks in advance

[run_ar]

Hi,

So even if ram retention is not enabled the chip does not actively reset the ram content. So the Ram content can be the same, but there is no warranty. It's likely that some bit's would change state. So if you need ram retention you should definitively enable it.

[Mathias Mitterdorfer]

Thanks for the reply,

I tested this yesterday with a custom application. The ram was always retained in SYSTEM OFF independent of the Settings for RAM Retention (not once that data got lost). I am just curious how this is technically possible as the capacitors in RAM should loose their voltage and hence the state should be lost (without constant refreshing).  

[run_ar]

hmm, Guess i don't really know how this works. But I would assume that since we are talking about sram, I do not think it has capacitors and need to be refreshed as is the case with dram. Most likely some of the current leakage in system off is caused by ram, but to be sure the content do not change over time ram retention has to be enabled to make sure it does not change state. increasing current consumption. One hint to this would be the workaround for Errata 108 that increases current consumption from 20 nA to 30 nA.