Meg93931:
Thanks! So I am trying to add the Arduino mega 2560 to a system that has an on/off button, and I want the Arduino to keep running from its previous point after the power is turned back on.
You're not being very clear. Do you mean you want to cut the power to the Arduino itself, then have it run from where it left off when it's power is reconnected? Or, while the Arduino is running, you just want to cut the power to the external device, then re-power it and have the Arduino sketch continue. And if the latter, do you want the Arduino to pause while the power to the external device is off?
What is this system that you mention?
If I hold down the reset button during upload, with this allow me to cut the power and turn it back on and the sketch to just continue where it left off?
Again, you're not explaining the situation very well.
Cut what power? Do you mean initiate an upload, press the RST button as it's happening and at the exact same time cut the power to the external device, or the Arduino, or both?
Words are free. Please describe the exact situation accurately, using as many as you need.