External inputs to a microprocessor

[barrygordon]

I'm using a 9S08AC32 in my design.  The board that I'm designing has connectors that external modules can plug-in.  When the modules is inserted, it pulls an I/O pin of the micro (pull-ups enabled) low.  My logic detects if the I/O pin is low then a module is plugged in.  I have 16 of these input pins.  Normally I would route these pins to a parallel load serial shift register and clock the results in.  Hopefully the module would only be inserted in when the power is off.  The connector is pinned so the module can only be plugged in one way.  I have 16 spared I/O pins.

Any thoughts and/or opinions on this on going directly to the I/O's.

thanks,

    Barry

[michaelsteffenf · Accepted solution]

Hi Barry,

There is no issues with connecting right to the microcontroller from the outside world, meaning the connector. The only thing that you will want to do is insert a 100 ohm resistor in series with all the spare i/o pins to limit any inrush current. Possibly add a 0.1uF cap to each line as well for filtering. We have many customers doing this in their designs as well.

Mike