Arduino data acquisition?

Hi everybody.

I have a nice Simulink program downloaded and running on my Arduino Mega 2560. The simulation does not run well in 'external mode' because my PC cannot keep up with the fast required simulation speed, however it runs fine when I download to the Arduino.

That being said, I need to collect data from my running program. I'm assuming I cannot do this in real time due to the above constraint (correct me if I'm wrong!), so I was thinking that maybe I need to store the data in the Arduino's memory somewhere and access it after my physical simulation has run.

How can I get this data I need?

Thank you very much!

What does "external mode" mean?

How much data (bytes per second) do you need to send to the PC?