Qusetion about DDR frequencies

[snoopy821215]

Qusetion about DDR

Hello, I have some questions about ddr.
Why can DDR only work on some specific frequency?
Why a 66Mhz DDR can not work on 60Mhz?
And is there any method to let 66Mhz DDR work on 60Mhz?

Waiting for your answer

 

[yibai]

Re: Qusetion about DDR

DDR400 of coz can run DDR266, DDR333.

Because of the DDR SDRAM's DLL, the DLL's delay chain just can lock above 100Mhz Clock. so if the DLL cannot lock the input clock, it will fail.

but i just can tell you that there is method to let ddr running on 60 Mhz.

 

[snoopy821215]

Qusetion about DDR

Hi yibai,

Thank you very much for your reply.
But it will be so good if u can tell me the method

Thank.
Regards,
snoopy

 

[littlebu]

Qusetion about DDR

actually frequecy of SDRAM and DDR core is also about 133MHz, just because DDR use a prefetch technique (it means parallel got data from MEM core, and send data serial). so when SDRAM upto DDR product, port accessed frequecy will up to double 133M, it is 266MHz. when it upto DDR2 will improve to 533M.

It is right?

Ps:I have another interesting question: why DDR data bus has named DQ, so D means Data, but what is this "Q"? Some people said it is I&O write together more like Q....... so it is right?

 

[yibai]

Re: Qusetion about DDR

actually frequecy of SDRAM and DDR core is also about 133MHz, just because DDR use a prefetch technique (it means parallel got data from MEM core, and send data serial). so when SDRAM upto DDR product, port accessed frequecy will up to double 133M, it is 266MHz. when it upto DDR2 will improve to 533M.

It is right?

Ps:I have another interesting question: why DDR data bus has named DQ, so D means Data, but what is this "Q"? Some people said it is I&O write together more like Q....... so it is right?

1. right.
2. maybe. JEDEC wants to say it DQ , it's DQ.

 

[snoopy821215]

Qusetion about DDR

DQ means Date I/O.
Q=I+O