powering arduino using regulated +5v?

I have a project where I'm using the arduino to communicate with another controller. That controller has a regulated +5v output. Can I safely input this to the 5v pin to power the arduino?

Thanks! Justin

I wouldn't do it if you have a USB cable plugged in as there is the potential to back-drive 5V into the computer's USB port.

The only other potential problem I see is the on-board voltage regulator. The datasheet does not specifically say whether it is safe to back-drive 5V into the output with 0V at the input, so I would assume it is not safe.

This is a serial arduino, so no issues with usb. But yeah... putting +5v on the output of the voltage regulator is what I was concerned about.

Well... no biggie. I just tapped into the +12v line on the other board and ran it through Vin.

I think I'll get an Arduino Pro Mini, since it can accept a regulated +5v for power.