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Thread: Is there a chip that combines both a single channel MOSI tri-state & CS pull-up?

  1. #1
    Senior Member+ MichaelMeissner's Avatar
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    Cool Is there a chip that combines both a single channel MOSI tri-state & CS pull-up?

    According to the SPI guide:


    Two hardware related issues are:
    • Add pull-up resistors for the CS pin (and D/C pin if used);
    • Make the MOSI pin for the device tri-state.


    I'm wondering if there is a single chip that combines both. I would imagine you would connect CS and MOSI inputs on one side and get CS and MOSI outputs on the other (presumably with VCC and ground thrown in).

    Something like:
    Code:
    Originally the connection would look like:
    
           Teensy            Device
           ------            -----
           3.3v -----------> Vdd
           Ground ---------> Ground
           MOSI -----------> MOSI
           SCK ------------> SCK
           CS -------------> CS
           MISO -----------> MISO
    
    With pull-up resistors this would become:
    
           Teensy                            Device
           ------                            -----
           3.3v ---------------------------> Vdd
           Ground -------------------------> Ground
           MOSI ---------------------------> MOSI
           SCK ----------------------------> SCK
           CS ---+-------------------------> CS
                 |
                 +---- 2.2k resistor ---> Vdd
    
           MISO ---------------------------> MISO
    
    
    If we have to add a a tri-state buffer this would logically be something like:
    
           Teensy                                     Device
           ------                                     ------
           3.3v ------------------------------------> Vdd
           Ground ----------------------------------> Ground
           MOSI ------------------------------------> MOSI
           SCK -------------------------------------> SCK
           CS ---+----------------------------------> CS
                 |
                 +---- 2.2k resistor ---> Vdd
    	     |
    	     +--- OE --> +----------+
                             |          |
           MISO ----> A ---> + tristate +--- Y -----> MISO
                             |          |
                  Ground --> +          +
                             |          |
                  Vdd -----> +----------+
    
    So I'm wondering if there is a combined chip:
    
           Teensy                                         Device
           ------                                         ------
           3.3v ----------------------------------------> Vdd
           Ground --------------------------------------> Ground
           MOSI ----------------------------------------> MOSI
           SCK -----------------------------------------> SCK
    
    
                          +-------------------+
                          |                   |
           3.3v ---> Vdd -+--> +----------+
                               |          |   |
                          +----+ 2.2k ----+ <-+
                          |    |          |
           CS -----> OE --+--> + -------- +-------------> CS
                               |          |
           MISO ---> A ------> + tristate +--> Y -------> MISO
                               |          |
           Ground -----------> +----------+
    Preferably in through hole or SOIC-8 (SOIC-6 if it exists). The primary motivation is to save real estate on my prototype boards, but not have to go to custom PCBs, or PCBs smaller than I can solder.
    Last edited by MichaelMeissner; 11-18-2019 at 09:07 PM.

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