Quick question about the sd card cs 10k pull up on teensy audio board.

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russdx

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Version one has not got a 10k pull up resistor on the cs sd card line.
Version two does have this.

Teensy 3.6 does not have the resistor either.

Is this 10k pull up required on the sd card cs line? If so why? Its just a gpio line and the software has full control over its output state.


I am adding a sd card to my custom board (to be used with the teensy audio lib) and just wondering if i need to add this resistor or not :)

One note the sd card will be the only SPI device on my board. Do i even need the cs line? Can i just ground it?

Regards
Russell
 
AFAIK- The pullup on the CS line is to make sure that when multiple devices are sharing the bus any not pulled low ignore the SPI bus. With a single device there won't be any contention or need for the pullup. It wouldn't be appropriate to have this on the Teensy itself as pins used for CS are numerous and when not used for SPI it would be inappropriate.
 
For the cost of a resistor, why not leave it in? If you're designing a custom board, I'd at least leave the pads for it.
 
But if its not needed no point having it :) This board will only have 1 spi device.

Regards
Russell
 
I’ve been burned too many times in my professional life with having to respin a board because of mistakes with device control / configuration lines. Devices may change or specs sheets may simply be incorrect or misinterpreted. Now, my group always routes these types of signals in a way that their connection can be changed without respinning the board -- at least for prototypes. Techniques include SMD pull-up / pull-down resistors (that can be populated or not), SMD zero-ohm resistors (that can be populated or not) connecting a control signal’s source to its sink, and surface PCB traces that can be cut.
 
Yup 100% agree if this board was going to be mass produced or used for development or used for some sort of shield etc... But in this case I will be making a one off pcb with absolutely only one spi device on board :D But it does not hurt to add a resistor foot print :)

Regards
Russell
 
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