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   XPost: sci.electronics.design   
      
   On 16 Jan 2024 15:57:32 GMT, Michael Schwingen   
    wrote:   
      
   >On 2024-01-16, John Larkin  wrote:   
   >>>If you want something nice with level translation that handles power   
   >>>sequencing between Pi and Target board, the JTAG Hat should do what you   
   >>>want:   
   >>>   
   >>>https://github.com/mschwingen/hardware/tree/master/JTAG_hat   
   >>>   
   >>>I think this should also work an a pi400.   
   >>   
   >> Is there a schematic somewhere?   
   >   
   >It is linked in the description:   
   >   
   >https://github.com/mschwingen/hardware/tree/master/JTAG_hat/pcb_ms_v3/Doc   
   >   
   >It's basically a bunch of 74LVC2T45 (which handle the "one side powered   
   >down" as well as the level-shifting), plus open-drain drivers for the reset   
   >signals. Note that you need to switch direction for the SWDIO signal, the   
   >rest is unidirectional.   
   >   
   >cu   
   >Michael   
      
   This is a first pass at the dev board.   
      
   https://www.dropbox.com/scl/fi/709v4pqjhe91jnwqh4wvg/Z566_Sch_2.   
   pg?rlkey=fjq3a9re53cv5l0zn9ya00akk&raw=1   
      
   It would be used in development and production test. Every   
   RP2040-based board would have the small-pitch 20 pin ribbon cable   
   header.   
      
   The pushbuttons look primitive but will probably work.   
      
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