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C.East2
Associate III
June 23, 2022
Solved

What is the Clock Speed of the SDRAM FMC on the STM32F469?

Once again I'm struggling to find a clear source for a peripherals clock with STM32 MCU's.

Most searching leads me to HCLK/2, so at a max HCLK of 180MHz I get 90MHz.

However, looking at there reference manual for the STMF469 I see this:

0693W00000NscFdQAJ.pngFrom an example linked here, I can see that the STM32H7B3LI has a divider to select the HCLK Division.

I cannot, however, see this option in MXCube for the STM32F469, but it says that the clock speed could be HCLK/3.

Any idea what's going on here?

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C.East2
C.East2Best answer
Associate III
June 23, 2022

Correct. I've found the divider in question, which CubeMX calls 'SDRAM common clock' which seems obvious but the parameter is of type 'HCLK clock cycles' where there selectable options are '2/3 HCLK clock cyles' when it's really a prescaler. This really needs to be made clearer.

4 replies

Tesla DeLorean
Guru
June 23, 2022

0693W00000Nscn6QAB.jpgPerhaps a deficiency in CubeMX, or looking in the wrong place. Or that 90 MHz is already under the typical 100, 133, or 166 MHz rated SDRAMs of the day, and you're likely not using 66 MHz parts.

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C.East2
C.East2AuthorBest answer
Associate III
June 23, 2022

Correct. I've found the divider in question, which CubeMX calls 'SDRAM common clock' which seems obvious but the parameter is of type 'HCLK clock cycles' where there selectable options are '2/3 HCLK clock cyles' when it's really a prescaler. This really needs to be made clearer.

Tesla DeLorean
Guru
June 23, 2022

I'm not sure it is a prescaler, the peripheral is a complex sequencer, it's running at HCLK internally.

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