Drive Strength Field specification

mplseng — Fri, 20 Jun 2014 16:21:52 GMT

I need to set the drive strength for some DDR pins to 40 ohms. The Vybrid manual does not explicitly specify the correct setting for selecting 40 Ohm if DDR.

Should I use 110 for 40 Ohm if DDR?

This is the excerpt from the manual

Vybrid Reference Manual, Rev. 7, 06/2014, p.221

Drive Strength Field. Select one of the following values for pad: PTA6.

000 output driver disabled;

001 150 Ohm (240 Ohm if pad is DDR)

010 75 Ohm (120 Ohm if pad is DDR)

011 50 Ohm (80 Ohm if pad is DDR)

100 37 Ohm (60 Ohm if pad is DDR)

101 30 Ohm (48 Ohm if pad is DDR)

110 25 Ohm

111 20 Ohm (34 Ohm if pad is DDR)

Thanks

Bob

Re: Drive Strength Field specification

jiri-b36968 — Mon, 23 Jun 2014 15:56:09 GMT

Hi Bob,

it is design specific: Trace length, PCB, memory. Nevertheless on TWR-VF65 rev.H (SDRAM and Vybrid are next to each other, without external termination) we are using DSE = 110. See below:

void setup_iomux_ddr(void)

{

#define DDR_IOMUX 0x00000180

#define DDR_IOMUX1 0x00010180

__raw_writel(DDR_IOMUX, IOMUXC_DDR_A15);

__raw_writel(DDR_IOMUX, IOMUXC_DDR_A14);

__raw_writel(DDR_IOMUX, IOMUXC_DDR_A13);

__raw_writel(DDR_IOMUX, IOMUXC_DDR_A12);

__raw_writel(DDR_IOMUX, IOMUXC_DDR_A11);

__raw_writel(DDR_IOMUX, IOMUXC_DDR_A10);

__raw_writel(DDR_IOMUX, IOMUXC_DDR_A9);

__raw_writel(DDR_IOMUX, IOMUXC_DDR_A8);

__raw_writel(DDR_IOMUX, IOMUXC_DDR_A7);

__raw_writel(DDR_IOMUX, IOMUXC_DDR_A6);

__raw_writel(DDR_IOMUX, IOMUXC_DDR_A5);

__raw_writel(DDR_IOMUX, IOMUXC_DDR_A4);

__raw_writel(DDR_IOMUX, IOMUXC_DDR_A3);

__raw_writel(DDR_IOMUX, IOMUXC_DDR_A2);

__raw_writel(DDR_IOMUX, IOMUXC_DDR_A1);

__raw_writel(DDR_IOMUX, IOMUXC_DDR_BA2);

__raw_writel(DDR_IOMUX, IOMUXC_DDR_BA1);

__raw_writel(DDR_IOMUX, IOMUXC_DDR_BA0);

__raw_writel(DDR_IOMUX, IOMUXC_DDR_CAS);

__raw_writel(DDR_IOMUX, IOMUXC_DDR_CKE);

__raw_writel(DDR_IOMUX, IOMUXC_DDR_CLK);

__raw_writel(DDR_IOMUX, IOMUXC_DDR_CS);

__raw_writel(DDR_IOMUX1, IOMUXC_DDR_D15);

__raw_writel(DDR_IOMUX1, IOMUXC_DDR_D14);

__raw_writel(DDR_IOMUX1, IOMUXC_DDR_D13);

__raw_writel(DDR_IOMUX1, IOMUXC_DDR_D12);

__raw_writel(DDR_IOMUX1, IOMUXC_DDR_D11);

__raw_writel(DDR_IOMUX1, IOMUXC_DDR_D10);

__raw_writel(DDR_IOMUX1, IOMUXC_DDR_D9);

__raw_writel(DDR_IOMUX1, IOMUXC_DDR_D8);

__raw_writel(DDR_IOMUX1, IOMUXC_DDR_D7);

__raw_writel(DDR_IOMUX1, IOMUXC_DDR_D6);

__raw_writel(DDR_IOMUX1, IOMUXC_DDR_D5);

__raw_writel(DDR_IOMUX1, IOMUXC_DDR_D4);

__raw_writel(DDR_IOMUX1, IOMUXC_DDR_D3);

__raw_writel(DDR_IOMUX1, IOMUXC_DDR_D2);

__raw_writel(DDR_IOMUX1, IOMUXC_DDR_D1);

__raw_writel(DDR_IOMUX1, IOMUXC_DDR_D0);

__raw_writel(DDR_IOMUX1, IOMUXC_DDR_DQM1);

__raw_writel(DDR_IOMUX1, IOMUXC_DDR_DQM0);

__raw_writel(DDR_IOMUX1, IOMUXC_DDR_DQS1);

__raw_writel(DDR_IOMUX1, IOMUXC_DDR_DQS0);

__raw_writel(DDR_IOMUX, IOMUXC_DDR_RAS);

__raw_writel(DDR_IOMUX, IOMUXC_DDR_WE);

__raw_writel(DDR_IOMUX, IOMUXC_DDR_ODT1);

__raw_writel(DDR_IOMUX, IOMUXC_DDR_ODT0);

}

/Jiri

Re: Drive Strength Field specification

mplseng — Wed, 02 Jul 2014 12:46:59 GMT

I asked the question incorrectly. I want to use 40 ohm drive strength. Does the drive strength setting of 110 correspond to 40 Ohm if DDR selected?

Bob

Re: Drive Strength Field specification

jiri-b36968 — Thu, 03 Jul 2014 07:24:50 GMT

Hi Bob,

Yes 0b110 correspond to 40 Ohm for DDR case. Confirmed by designers. Sorry for missing information in RM.

/Jiri

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