MMC1: strange voltage values in MMC1 module pins DAT[3-0], WP and CMD

Hello, I built a board really similar to beagleboard rev4 from scratch. I just added some USB ports and other few changes.(buy the components, manufacture it, design the layers…etc)
After some problems I finally got a “40W” in the terminal connected to UART3. I could not boot from SDCard because, despite the voltage in VMMC1 is 3V, my WP, DAT[3-0] and CMD pins have a strange voltage value. The voltage values measured in the SDCard reader are shown in this table:


0.5 V | | 1.8 V | WP | | Conected to OMAP | | |
1.8 V | | 1.8 V | CD | | Conected to TPS65950 | | |
0.51 V | | 3 V | DAT1 | | Conected to OMAP | | |
0.507 V | | 3 V | DAT0 | | Conected to OMAP | | |
0 V | | 0.078 V | DAT7 | | Conected to OMAP | | Powered by VSIM |
0 V | | 0 V | GND | | | | |
0 V | | 0.072 V | DAT6 | | Conected to OMAP | | Powered by VSIM |

CLK | | Conected to OMAP | | |
3 V | | 3 V | VDD | | | | |
0 V | | 0 V | GND | | | | |
0 V | | 0.072 V | DAT5 | | Conected to OMAP | | Powered by VSIM |
0.5 V | | 3 V | CMD | | Conected to OMAP | | |
0 V | | 0.073 V | DAT4 | | Conected to OMAP | | Powered by VSIM |
0.513 V | | 3 V | DAT3 | | Conected to OMAP | | |
0.507 V | | 3 V | DAT2 | | Conected to OMAP | | |

After check the voltages in a real beagleboard I found that DAT[0-3] and CMD are 3V. I have been searching a lot but I could not find why my voltage values are wrong.

The hardware configuration is the same as the original beagleboard: to power OMAP3530 I am using TPS65950. The only difference is that due to a design fail I needed to cut the connection of VMMC1 with the TPS65950 and I am powering VMMC1 with an external source (3V). I took care of give power to VDD in the card reader and to VDDS_MMC1 in the OMAP3530.

VSIM is 0V after reset despite VAUX12S is powered at 3.6V. I could not load any loader into the board yet. If I can not fix MMC problems I will try to boot from UART, because of the 40W it seems that the OMAP processor is alive.

Really thanks.


  1. Because all the wrong voltages in my board are almost the same value (0.5 V) I thought that maybe the original beagleboards comes with a different preconfigured pins state-after-reset (pull-down or something) than the OMAP3530 bought directly???

  2. Can I say that VMMC1 is reaching correctly the VDDS_MMC1 pin in the OMAP3530 because of the 0.5V in the pins? or the connection between VMMC1 and VDDS_MMC1 could be cut despite the 0.5V?

Well, not much to go on here. A schematic would be extremely helpful. Configuration of pins are taken care of by the internal ROM and are shown in the datasheet. I would also look at your boot pins, but i have no idea where they are connected to.


Thanks for your answer. Feel free to ask me any details about the board if you suspect about something.
The schematic is almost the same as the beagleboard rev4 one, I just added some new ports. The DAT pins, CMD pin, WP pin and CLK pin of the mmc module are connected to the same pins in the OMAP as the original beagleboard. I attach here an image of the sysboot pins. My PLL2, VSIM and VDAC voltages are 0V after reset, but they do not matter because they are not needed to boot from mmc (or I thought that after check TPS and OMAP datasheets)


Screen Shot 2014-03-26 at 01.57.26.png

Ok, thanks for your help, I finally got it. My SYS_BOOT configuration was wrong: I inserted also the “do not insert” resistors. After removing them the card module worked and I was able to boot.
The 0.5V is the voltage that you can measure in a pin that has an active pull-down: after fixing the SYS_BOOT the OMAP tried to boot from mmc and it disabled the pull-downs in the mmc pins before attempting to boot from card.