I plan to connect SDRAM from the MICRON MT48LC series (datasheet). The pin connection diagram is generated automatically by STM32CubeMX (STM32H743). The setting is an 8-bit data bus, a 13-bit address, 4 banks, and clock and chip enable (SDCKE0 + SDNE0).

However, I found that there is no pin to connect to the Micron DQM pin. I saw some suggestions that if there is no use for DQM pin, it should connected to GND (waclawek.jan answer), and also Micron suggests to leave it NC (float) (the section "Unused DQ Pin").

I dug into the truth table of the Command and DQ pins. this is the table:

The DQM signal is used for READ and WRITE operations and also "Write enable/output enable" and "Write inhibit/output High-Z". It seems that connecting DQM to GND for logic "L" is better than letting it float. This is the thing that is very unclear. How could I connect an STM32 with the Micron SDRAM DQM pin?

  • \$\begingroup\$ It is an input so yes, you should not let it float. \$\endgroup\$
    – dim
    Commented Feb 14, 2019 at 3:42

1 Answer 1


If you look at section 21.9.2 of the STM32H743 manual (shown below), you can see that the DRAM controller does have the ability to drive the DQM pins. Perhaps it is the auto generate that is not working. For an 8 bit interface, DQM on the SDRAM would likely connect to NBL0.

Section 21.9.2

The STM32H743 datasheet shows that NBL0 is connected for all packages:

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  • \$\begingroup\$ NBL0 is available when I use the 16-bit data bus. However, this pin is not available in 8-bit data bus in STM32CubeMX \$\endgroup\$
    – MooMoo
    Commented Feb 14, 2019 at 4:48

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