Various behaviour of two identical SD cards


I have a following issue with SanDIsk SDHC 8GB Class 4 cards. My board is APU2C (board’s schematics).

I have two copies of those cards wich seems to be identical. According to their CID numbers, they both have been manufactured in 11/2015. The only difference I have spotted is their PSN (serial number).

One card (marked as GOOD - G) works properly 100% of the time. The problem is with the other one (marked as BAD - B) when it is inserted in SDHC slot before the board is powered on (which is rather typical usage of SD cards). Then it neither appears in bootmenu, nor is visible in the OS. The only way I have managed to make it work again is to reinsert (hotplug) when the board is already powered on (it does not matter if it occurs in bootmenu or in OS). From that point card works just like the GOOD one, even after multiple reboots. Next coldboot makes it to block again. Note that a warmboot won’t make it work - it is being blocked unless reinsert happens, which seems to be a critical action. In this state BAD card does not respond  to any SD commands (timeout).

During debugging I have also spotted the difference in internal pull-up resistor operation between those cards.  In case of a GOOD card, it is enabled at the same time as voltage appears on the card. On the contrary, it is not enabled at all in BAD card when it is blocked. After hotplug internal pull-up in BAD card is also enabled - just like in the GOOD one. I know it might be used for card detection (which is not the case for me, because this board uses mechanichal switch for this purpose). It may not be the reason itself why it’s being blocked, but I think it’s at least a symptom of malfunction. In the end I have also applied voltage from the board directly to the BAD card and internal pull-up was enabled so it suggests that the voltage itself is not the problem.

BAD card boots properply on RPI, so it may be board issue. Nevertheless I would like to know if You had encountered similar issue in the past or have any knowledge what may cause the potentially identical cards to behave differently.

Below are CID and PSN of both cards:

  • GOOD



  • BAD