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STM32F4 Discovery FSMC Problem

Posted on January 12, 2016 at 14:06

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14 REPLIES 14
Posted on January 20, 2016 at 14:45

Does STM32F429I-Discovery board's ISSI SDRAM work with sinusoideal clock pulse on SDCLK pin?

Posted on January 20, 2016 at 15:07

I haven't looked, but they do drive the pins in 50MHz mode (slew rate setting), not the 100MHz mode.

The waveform will be impacted by the capacitive load that it is being driven into.

Also make sure to use your scope probe in 10x mode, the bandwidth in 1x mode is likely awful.

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Posted on March 18, 2016 at 16:01

Thank you clive1 I saw it now too. But why coders clocking the SDRAM with 90MHz (in FMC_SDRAM sample on STM32F429I-Discovery) but pins are 50MHz? Can they want to reduce over and undershooting of the clock pulses?

Posted on March 18, 2016 at 17:33

The frequency number is a bit of a misnomer, the setting is defining how aggressively, in terms of energy imparted in the pin driver.

To escape the part, the pin driver typically has a cascading chain of inverters, with bigger and bigger transistors, permitting high instantaneous current to change the state of the signal into a capacitive load.

The setting you need is going to depend on your board traces, and the input characteristics of the SDRAM. And if you have multiple SDRAM, etc.

If you can balance the settings, then you'll reduce the overshoot, undershoot, and ringing.

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Posted on March 30, 2016 at 17:18

Thanks for your informative answer clive1