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pull up/down recommendation for external data bus of S12

Question asked by Leopold Gemsch on May 8, 2017
Latest reply on May 9, 2017 by lama

Dear all,


we are operating a MC9S12XDP512 / MC9S12XEP100 micro controller in expanded mode. On the external bus a static RAM IC is connected without external pull up / down resistors on data bus.

What is your the recommendation regarding pull up / down resistors:

  • do we need pull up or pull down at all on the external data bus to have a defined signal level in case the external static RAM IC is not accessed?
  • should / can we make use of the internal pull up feature of PORT C / D to have defined signal levels on the external data bus (set PUPDE PUPCE in PUCR register)?
  • should we better use external pull up / down resistor to have defined signal levels on the external data bus?
  • is there an application note about this topic and where do we find it?


We are looking forward to get an answer to the questions soon.



With kind regards