Pin state when micro is turned off

[lpcware]

Content originally posted in LPCWare by mattiad on Tue Dec 30 00:40:10 MST 2014
Hi everybody,

I'm using an LPCU68 in a particular circuit. In the circuit I use two different supply sources and I turn off the micro in order to go in “power-saving” state (another micro is connected to another suplly and it's always on).
When the LPC is turned off, are all the pins in a not-well-known state? I mean, can some pin be in a high or low logical state with low impedance and draw-source some current?
Is it possible to have all of these in high impedance state?

Best regards

[lpcware]

Content originally posted in LPCWare by arw on Tue Dec 30 11:06:53 MST 2014
Hello,
If the device is not powered, then the state of the chip is completely undefined.  It is dangerous for another device to drive any voltage in a circuit that connects to an IC that is powered off.  Either IC may be damaged since the IOs are not in a controlled state. 

If you want to ensure that the device is in a known state, then try using Deep Power-Down mode, for example, which holds all pins (except WAKEUP) in tri-state mode.  This will require that you keep an active power supply to the device.

If you must power-off the part of the system where this MCU is included, then all connecting circuits in the powered-on area should be high impedance, and must not drive a voltage on these connecting paths.

-arw