rbeyer
Posts: 3
Joined: Mon Sep 18, 2017 6:08 pm

CM3 Can't Access SD Card on Custom Board

Mon Sep 18, 2017 6:27 pm

I'm having an issue with a custom CM3 carrier board. Attached is the schematic that I'm using. I've tried to duplicate the EMMC_DISABLE_N logic and EMMC_EN_N logic as close as possible to the CM3 development board. Q1/Q7 is a AO3414 N-Channel MOSFET 20V/4.2A (https://www.digikey.com/products/en?key ... -1009-1-nd).

The board works when the SD card is not inserted and used with a CM3 (booting from EMMC), but does not work when a CM3L and SD Card is inserted in the slot. I've tried to make the SDX_D0-D3/CMD/CLK traces as equal length as possible (within 100 mils) and minimal via's (max 2 per line). Lines are all 10 mils with a 6 mil spacing.

Can anybody see what I'm missing?
SD Access Issues.PNG
SD Access Issues.PNG (33.3 KiB) Viewed 414 times

rzusman
Posts: 293
Joined: Fri Jan 01, 2016 10:27 pm

Re: CM3 Can't Access SD Card on Custom Board

Sat Sep 23, 2017 11:10 pm

Your schematic looks like mine, except I simply tied pin 2 (/EMMS_DISABLE) to +3.3V.

I didn't take any particular precaution about keeping my traces all the same length, although they are all pretty short (< 2"). Are you sure that /EMMS_DISABLE is high? Scope it and see.

rbeyer
Posts: 3
Joined: Mon Sep 18, 2017 6:08 pm

Re: CM3 Can't Access SD Card on Custom Board

Mon Sep 25, 2017 8:25 pm

Thank you, I'll check. I tried soldering the pin high on one board revision but it did not produce any results. I've got a new board revision on the way and I will try it with that.

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