Sourcing and sinking currents for AT89S51

This may seem like a really stupid question..but how do we know what is the maximum current a micro controller can source or sink for logic 0 and 1....there are various currents given in the datasheet.. but i dont know which ones to read...
Can anybody tell me the values for AT89S51..

Page 20 of the attached datasheet has the current ratings with respect to port pins as well as ports.

Sink current is Iol i-e current o/p low.

Source:Maximum DC o/p current is listed on the same page.

It there but this is it in a nutshell

Port 0: 26 mA Ports 1, 2, 3: 15 mA
Maximum total IOL for all output pins: 71 mA

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