What is the maximum and minimum current sourcing and sinking capacity of blackfin PF(Flag) pin?
You should check the datasheet for the particular model of Blackfin Processor. There are several places that drive current is mentioned in the datasheet. In absolute maximum ratings section there may be a maximum (maybe 80ma or more) for a group of I/O pins that should not be exceeded. Secondly there are IV curves published for each driver type. These are typical curves at room temperature and therefore should be used cautiously.
Drive to typical logic inputs is never a problem. Logic inputs require only microamps or less. The logic fan-out is limited only by the rise and fall reduction or total capacitance (also found in the datasheet).
There would be no problem if you drive 20ma to a single LED. If on the other hand you want to use 50 ohm termination to ground on output signals, that would not be recommended.
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