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Using EMC SDRam with diffrent frequency

Question asked by Friedbert Maier on Nov 13, 2017
Latest reply on Nov 15, 2017 by jeremyzhou

We are using a LPC1778FET208 with a SDram IS42SM16800H.

And we have the problem, that the SDram only works with a frequency of the SDram between 18MHz and 38 MHz. It is not possible to use a higher or a lower frequency.

It doesn't matter if we choose the controller frequency or we use the double frequency of the Controller and set EMCCLKSEL=1 to use the half frequency.

In EMCinit we take the timings of the SDram Datasheet. If we take wrong timings (to short or to long) it doesn't work. So we think we have the right values for this timings. And it doesn't mater if we use RAS& CAS = 2 or RAS&CAS =3.

 

We also tested the Timings with different values in the delay Registers (EMC_CMDDLY and EMC_FBCLKDLY). If we use here high values > 20 then it works with no frequencys.

 

To take the right mode on the SDram we read the mode with the following funktion: dummy = *((volatile unsigned long *)(0xA0000000 | (3<<0 | 3<<4)<<10). So we have Burst length = 4, CAS Latency =3 and 9 column_bits in the BRC mode.

 

 

 

And we also checked the path length on the pcb borad. Here are no big differences between all the different lines between the controller and the SDram.

 

So do you have any futher idea what we can check to use this SDram with different frequencies.

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