You wrote:
>Ok, so far so good, one cannot do that. So the question is: How do I
compute
>the maximum current a given chip can source at a time? I need to drive
>several charges at (possibly) the same time and I am afraid of overloading
>or overheating the PIC. I guess that if I find that it is too much for the
>PIC I'd have to use transistors for driving my output charges.


You have to check the maximum Power dissipation the device can handle.
Pdis=VDDx{IDD-SUM IOH} + SUM{(VDD-VOH)xIOH} + SUM(VOLxIOL)

Holp this help.

Marcelo Y.
m_yamamoto@uol.com.br