What is the function of the DQS line with SDRAM?

[gerry1]

What is the purpose and function of the DQS signal in the SEMC SDRAM interface?

[Alessandro_Morgan]

Dear Felipe,

You reported here:

"The recommendation is to leave the pin floating and internal loopback enabled as this is needed for SDRAM read and write operations at 166 MHz, otherwise performance will not be optimal."

This seems to conflict with the IMXRT1064 datasheet where if the loopback is set internal (SEMC_MCR.DQSMD = 0x0) the minimum setup data time is 8.67ns resulting in a maxim speed of around 115MHZ since Hold time is 0ns.

Is it something I am missing?

Moreover if we set the "external loopback" how the SEMC_DQS trace have to be routed in PCB?
Just leave the pad unconnected without any trace?

Kind Regards,

Alessandro

[FelipeGarcia]

Hi Gerry,

DQS signal is to compensate the delay of data path and clock.  Certain devices use this pin to indicate the dummy cycles needed (before Program/Read data transfer).

Best regards,

Felipe

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[gerry1]

Hi Felipe,

Thanks for the response however you don't explain how this is signal is used in the RT1050 with SDRAM. Is it an input to the 1050? If so, how is it used internally and how is it normally connected to external circuitry?

Regards,

Gerry

[FelipeGarcia]

Hi Gerry,

SEMC_DQS is input/output when the MCU writes data to the SDRAM, it outputs the DQS in the center of the data it is writing. When reading data, the SDRAM sends the DQS edge aligned with the data.

The recommendation is to leave the pin floating and internal loopback enabled as this is needed for SDRAM read and write operations at 166 MHz, otherwise performance will not be optimal.

Best regards,

Felipe

-------------------------------------------------------------------------------

Note:

- If this post answers your question, please click the "Mark Correct" button. Thank you!

- We are following threads for 7 weeks after the last post, later replies are ignored. Please open a new thread and refer to the closed one, if you have a related question at a later point in time.

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[gerry1]

Hi Felipe,

Thanks for the information and the recommendation not to use the DQS line. However, I would like to understand it's function in detail. Is there documentation about this functionality with timing diagrams?

Regards,

Gerry

[FelipeGarcia]

Hi Gerry,

You can find timing diagrams in our Reference Manual.

Regards,

Felipe