Wrong DQS Out for DDR SDRAM driven at low frequency

[cafukarfoo]

DQS Out for DDR SDRAM

Hi Sir/Madam,

I noticed that if i run the DDR SDRAM at lower frequency for example 50/75MHz, the dqs out coming out is wrong.

For burst of 8, there is 5 pulse of dqs out instead of 4 pulse.

Do you have any idea what happen here and how to prevent that from happening?

Thanks.