SDRAM refresh cycle / LPC_EMC->DYNAMICREFRESH / Finding correct value

lpcware — Wed, 15 Jun 2016 18:47:41 GMT

Content originally posted in LPCWare by hlsa on Sun Sep 27 23:05:42 MST 2015
I am using the LPC4357 @ 204 MHz with 102 MHz EMC clock and an ISSI IS42S32800G-7BLI SDRAM.
The SDRAM requires 4096 refresh cycles every 64ms.

So far I have set the dynamic refresh register LPC_EMC->DYNAMICREFRESH to 100. If I understood the user manual correctly, this equals a refresh cycle time of 100 * 16 * 4096 * 1/102MHz = 64.25ms.

If I understand it further correctly, this is too long and I would need a value for LPC_EMC->DYNAMICREFRESH, which is a little bit lower, e.g. 98 * 16 * 4096 * 1/102MHz = 63 ms.

Am I correct? Can anyone please confirm this?

Many thanks,
Holger

P.S. My system works pretty fine. However, since reliability of our products is extremely important, I do not want to run anything out of spec.

Re: SDRAM refresh cycle / LPC_EMC->DYNAMICREFRESH / Finding correct value

lpcware — Wed, 15 Jun 2016 18:47:42 GMT

Content originally posted in LPCWare by mc on Tue Sep 29 06:23:08 MST 2015
Hi Holger,
Your formula to calculate refresh time is correct. The programmed refresh time should be less than 64ms.

topic Re: SDRAM refresh cycle / LPC_EMC->DYNAMICREFRESH / Finding correct value in LPC Microcontrollers

SDRAM refresh cycle / LPC_EMC->DYNAMICREFRESH / Finding correct value

Re: SDRAM refresh cycle / LPC_EMC->DYNAMICREFRESH / Finding correct value