Ruth Hendrix

floating inputs and unpowered devices

Discussion created by Ruth Hendrix Employee on Jan 24, 2006
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Posted: Tue Sep 27, 2005 7:11 pm    
Is there any danger of floating inputs (on HC08) connected to device output that is un-powered - power have been taken away from the device via FET, but processor power still remains. This is low power state, and GP32 is but in STOP. Will the GP32 and/or the external unpowered part (output) be sufficient always without failure to keep port pin low (and therefore not floating) ???
Posted: Thu Sep 29, 2005 1:51 pm    
If the HC08 variant you're using has optional pull-up resisters on the inputs enable them, place your circuit(s) in sleep-mode and see if the inputs are pulled up (to HC08 Vdd).
Alternately, you can provide external pull-down resistors. I don't think I would leave them floating.
Posted: Thu Sep 29, 2005 11:01 pm 
Do not under any circumstances leave floating inputs on any digital logic. especially if you are expecting a "low power" mode.
Floating inputs can be expected to settle at the point where the port pin absorbs its maximum current.