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well, this is awkward 74HC238 vs 74HC11238

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  • bill rowe
    when I was laying out the PCB for the olduino shield adapter I grabbed the symbol for the 74AC11238 from the eagle library not realizing it was different from
    Message 1 of 3 , Oct 31, 2013
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      when I was laying out the PCB for the olduino shield adapter I grabbed the symbol for the 74AC11238 from the eagle library not realizing it was different from the 74HC238. You often have to choose something with the same footprint e.g. 7404 or 74ls04 rather than 74c04.  

      The 74AC11238 part has the same name and function as the 74HC238 and the pins have the same names but they're moved around.  For example the 74AC11238's VCC and GND are on 12 and 4 vs the 74HC238's more traditional 16 and 8.  Comparing the datasheets the 74AC1138 is MUCH faster than the 238 but sadly digikey doesn't actually have any so I guess I'll be using one of my extra footprints.


    • s_brune2001
      To avoid using your extra footprints you could always mount the chip dead bug style, use wire wrap wires and solder them from the pads to the correct chip
      Message 2 of 3 , Nov 1, 2013
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        To avoid using your extra footprints you could always mount the chip dead bug style, use wire wrap wires and solder them from the pads to the correct chip pins.



        ---In cosmacelf@yahoogroups.com, <bill_rowe_ottawa@...> wrote:

        when I was laying out the PCB for the olduino shield adapter I grabbed the symbol for the 74AC11238 from the eagle library not realizing it was different from the 74HC238. You often have to choose something with the same footprint e.g. 7404 or 74ls04 rather than 74c04.  

        The 74AC11238 part has the same name and function as the 74HC238 and the pins have the same names but they're moved around.  For example the 74AC11238's VCC and GND are on 12 and 4 vs the 74HC238's more traditional 16 and 8.  Comparing the datasheets the 74AC1138 is MUCH faster than the 238 but sadly digikey doesn't actually have any so I guess I'll be using one of my extra footprints.


      • bill rowe
        Good point but this is exactly what they re for. The extra footprints have dual holes so i can jumper from old pads to proper pads very easily - all the while
        Message 3 of 3 , Nov 1, 2013
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          Good point but this is exactly what they're for. The extra footprints have dual holes so i can jumper from old pads to proper pads very easily - all the while repeating "check the connections *before* you send the gerbers!"

          if i'd done a ground/vcc check on the layout i would have spotted it right away. 

          On 20-11-01, at 8:56 AM, s_brune@... wrote:

           

          To avoid using your extra footprints you could always mount the chip dead bug style, use wire wrap wires and solder them from the pads to the correct chip pins.



          ---In cosmacelf@yahoogroups.com, <bill_rowe_ottawa@...> wrote:

          when I was laying out the PCB for the olduino shield adapter I grabbed the symbol for the 74AC11238 from the eagle library not realizing it was different from the 74HC238. You often have to choose something with the same footprint e.g. 7404 or 74ls04 rather than 74c04.  

          The 74AC11238 part has the same name and function as the 74HC238 and the pins have the same names but they're moved around.  For example the 74AC11238's VCC and GND are on 12 and 4 vs the 74HC238's more traditional 16 and 8.  Comparing the datasheets the 74AC1138 is MUCH faster than the 238 but sadly digikey doesn't actually have any so I guess I'll be using one of my extra footprints.


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