STM32H7 FMC - SDRAM byte and bit swapping

JF999 · ‎2025-05-13

Hi

I am working on a project with an STM32H743 and a 32-bit SDRAM

The FMC signals are quite randomly scattered across the package and this makes layout quite convoluted and difficult. I'd like to swap byte-lanes and individual bits within each byte, for example:

- connect DQ0 - DQ7 on the SDRAM to DQ24 - DQ31 on the microntroller, then swap the mask signals DQM0 with DQM3.

- swap bits within a byte, for example after swapping the bytes as above, connect DQ0 to DQ25 on the micro and DQ1 to DQ24 on the micro.

The SDRAM should not care about these type of swaps, but are there any restrictions in the way that the FMC works that would stop this from working?

Thanks

mƎALLEm · ‎2025-05-20

Hello,

You can swap the positions of the byte lines but also swap their DQMx accordingly.

And if you need to swap the lines, you need swap them inside the byte.

Hope I answered your question.

To give better visibility on the answered topics, please click on "Accept as Solution" on the reply which solved your issue or answered your question.

View solution in original post

JF999 · ‎2025-05-19

Hi,

Does anyone have any thoughts on this at all?

mƎALLEm · ‎2025-05-20

Hello,

You can swap the positions of the byte lines but also swap their DQMx accordingly.

And if you need to swap the lines, you need swap them inside the byte.

Hope I answered your question.

To give better visibility on the answered topics, please click on "Accept as Solution" on the reply which solved your issue or answered your question.