pull up/down recommendation for external data bus of S12

[leopoldgemsch]

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

Leopold

[lama]

Hi,

a) as a first step I would like to direct you to my supporting material:

https://community.nxp.com/docs/DOC-93594

Please read it carefully. It will simplify your design and debugging issues.

b) No there is no reason to have any pull resistor on the bus.

If you have any additional questions, do not hesitate to ask....

Best regards,

Ladislav