In Section 18.104.22.168.3.6 of AM335x TRM
For RTC only mode only the RTC power supply is expected to be ON. All the remaining supplies are expected to be OFF. For SDRAM to be in self-refresh during this mode, the CKE pin of the DDR interface needs to have a pull-down on the board.
please suggest solution to pull down CKE externally to achieve the RTC only mode when SDRAM is in self refresh mode.
Thanks and Regards
I was looking into using a similar mode, just keeping the RTC running, but it seems there is an errata for the RTC
Have you been able to implement the RTC only mode successfully?
For some reason the post did not allow me to past a picture of the errata section, Advisory section 1.0.5 for Silicon Rev 1.0 the errata was revised May 2012.
During RTC only mode, if you want to put the DDR in self-refresh, you can add an external weak pull down resistor on CKE pin of the AM335x processor. We don't anticipate any issues with this approach.
We have not seen that approach in any of TI design. Could you please suggest any design with approach (mentioned in the above post).
We have one of our internal boards modified to test this and atleast a couple of our customers have implemented the same approach as I suggested earlier.
In continuation with the RTC only mode question, there seems to be a requirement that RTC_PWRONRSTn pin should be low for atleast 1 ms after VDDS_RTC has been applied. Can I use a RC netwrok to delay this signal and if so, is it ok if the rising edge is slow. Are there any requirements on the rise time of this signal?
One more question is it mandatory to pull down CKE to run DDR in self refresh mode?
Yes. CKE has to be driven low during self-refresh for DDR2 memories. Please also refer to the JEDEC Memory specs for requirements on self-refresh.
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