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If a logic high signal (+5V) comes from another IC or from a power source continuously via a resistor to the PIC input pin, do I still need another resistor between the PIC input pin & GND?
Hi Eric
Yes the power source is 5V not 12V.I need to detect it is available or not by every time polling that pin.In this case do I need another resistor between the PIC input pin & GND?
Hi its a 4.7K.I need to detect if the 5V source is there or not, so it can activate the battery backup in my timer project when power goes down.So I'm polling a pin every time.
The pull down resistor is needed to avoid the input from floating. I'm just wondering why do you need another resistor connected from the power source to the input pin?
If you use both a series and pull down resistor at the same time you must insure that the resulting 'voltage divider' action does not reduce the 5v down to a level less then the input will treat as a 1 or high. The pull down should be higher value then the series resistor.
Main btfss PORTA,RA4
goto Main ;power has gone
goto Normal ;power is there
Hi i'm using a 4.7K series resistor & 22K resistor go GND from PIC pin.
Is it good to detect the logic HIGH?