Reading a Controller Pak - dkidd928/cartreader GitHub Wiki
First you need to setup the Cart Reader Shield's configuration switches like so:
Doublecheck that the voltage switch is set correctly to 3.3V and that the EEP switch is set to enabled(=towards the back). This connects a 1K pull-up resistor between VCC and the controllers data pin(PH4).
Next plug a N64 controller into the controller plug and insert a Controller Pak into the Controller. Navigate to Nintendo 64 and then to Controller.
You can use http://rawgit.com/bryc/mempak/master/index.html to manage saved Controller Pak data on your PC.