In the i.MX RT1050 EVK SDRAM example, the project sets SEMC_DQS pin
IOMUXC_SetPinMux(IOMUXC_GPIO_EMC_39_SEMC_DQS, 1U); /* Software Input On Field: Force input path of pad GPIO_EMC_39 */
IOMUXC_GPIO_EMC_39_SEMC_DQS, /* GPIO_EMC_39 PAD functional properties : */
0x0110F9u); /* Slew Rate Field: Fast Slew Rate
Drive Strength Field: R0/7
Speed Field: max(200MHz)
Open Drain Enable Field: Open Drain Disabled
Pull / Keep Enable Field: Pull/Keeper Enabled
Pull / Keep Select Field: Keeper
Pull Up / Down Config. Field: 100K Ohm Pull Down
Hyst. Enable Field: Hysteresis Enabled */
But this pin is not connected in the EVK schematic. We are now working on our board and this pin is used for a different purpose. If we configure the pin like above, SDRAM somehow works but we break the other functionality.
It seems "Software Input On Field" is must otherwise the SDRAM does not work. But how a not-connected pin affects the SDRAM? Is there any internal mechanism for the SEMC module for SDRAM? If so, we might consider modifying the board which leaves the pin empty (or connected to the ground like as EVK)
Any idea? Thanks.
Hi Murat Cakmak
Please see below table from the Reference Manual:
If you going to use the SEMC module, in some cases this pad needs a pull-down resistor, this is why this pin is configured with a pull-down resistor.
Hope this helps