demedeirosa
Posts: 12
Joined: Wed Jul 11, 2018 1:57 pm

SDX Termination

Wed Jul 18, 2018 12:20 pm

Hi All,

Working on a design for a CM3, but I am including SD card provisions for a CM3 Lite since it looks like stock on the CM3 is limited currently.

I reviewed the schematic, and it appears that none of the SDX_x lines are terminated. Is there a particular reason why? All documentation i've come across regarding SD mentions termination resistors, and i have included it in past designs for other SoM PCB developments.

Thanks!

EDIT: I should clarify that this regarding the CMIO PCB reference design.

gsh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 1282
Joined: Sat Sep 10, 2011 11:43 am

Re: SDX Termination

Thu Jul 19, 2018 4:34 am

Termination of the signals is done inside the SD card. We also have pulls on the lines to 3v3 in the pads enabled so you don't need those. Although it has been noticed that some SD cards (specifically industrial quality SD cards) would benefit from an external pull down on CLK to stop it from floating and upsetting the FTL.
--
Gordon Hollingworth PhD
Raspberry Pi - Director of Software Engineering

demedeirosa
Posts: 12
Joined: Wed Jul 11, 2018 1:57 pm

Re: SDX Termination

Thu Jul 19, 2018 3:07 pm

Thanks for the information!

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