SD card slot

Card detection CD and write protection WP

Sdks do not have uniform physical specifications for WP, CD, and comm.
But for Pin 1 ~ 9 have unified specifications. pin sequence is 8, 7, 6, 5, 4, 3, 2, 1, 9

Card detection CD and write protection WP achieves mechanical connection between WP and CD to distinguish whether the card is inserted and whether there is write protection.
Comm is the common pin of WP and CD, So If comm is connected to the location, WP and CD must use the pull-up resistor to pull to VCC. Otherwise, if comm is connected to VCC, then WP and CD must use the pull-down resistor to pull down to Gnd.

When
When the card is inserted, the metal connections connected to comm in the card slot will make comm short-circuited with CD due to the card insertion (this process is related to whether the card is inserted or not, that is, the insertion duration between comm and CD occurs.
If the CD is pulled up, comm must be connected to the ground during design. In this case, after two pins are short-circuited, the status displayed on CD is Comm.
--- Gnd.
Similarly, WP is also such a process, but due to comm's mechanical shape design problems, the SD card's mechanical write protection operation will directly decide whether comm and WP
Pin short circuit. (This is a very interesting mechanical design. inserting a card does not determine the short circuit between WP and comm, but the write protection mechanical design of the SD card itself (such as the part circled by the Green frame) determines whether the card can be enabled.
Write protection implemented by the slot)

 

 

Card slot: 111110 P, axa2r73061

When no card slot is inserted, sdw.wp and sdw.cd # are open. sdw.wp: 3.26 V, sdw.cd #: 3.26 v
When inserting a card slot:
(1) When the SD card is locked,
Sd1_wp: 3.26 V, sd1_cd #: 0.03 v
(2) sdw.wp and sdw.cd # short circuit when the SD card is locked
Sd1_wp: 0.06 V, sd1_cd #0.06 v