alexan_e
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Sink (pull) current is when you have a load connected to the positive supply and you provide the ground to it so that the current can flow, for example a led with the anode to the positive supply (through a resistor) and you provide the gnd to the cathode so that the current can flow.
Source current is exactly the opposite, it is when you provide the positive supply to a load that is connected to the ground.
The open drain/collector is actually a ground side switch that can either turn on and provide the ground to the connected load (and let the current flow) or turn off (high resistance) and leave the output floating (no current flow).
In addition when there is a pull up resistor connected to the collector/drain of that low side switch then the output instead of floating is pulled up, but the current it can provide depends on the pullup resistor value.
In your case PORT0 has no pull up resistor and PORT1,2,3 have internal pullup resistors.
Alex
Source current is exactly the opposite, it is when you provide the positive supply to a load that is connected to the ground.
The open drain/collector is actually a ground side switch that can either turn on and provide the ground to the connected load (and let the current flow) or turn off (high resistance) and leave the output floating (no current flow).
In addition when there is a pull up resistor connected to the collector/drain of that low side switch then the output instead of floating is pulled up, but the current it can provide depends on the pullup resistor value.
In your case PORT0 has no pull up resistor and PORT1,2,3 have internal pullup resistors.
Alex
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