In the datasheet for the 887, it says:

---
Maximum output current sunk by any I/O pin:  25 mA
Maximum output current sourced by any I/O pin:  25 mA
Maximum current sunk by all ports (combined):  90 mA
Maximum current sourced by all ports (combined):  90 mA
---

Now let's say I take 4 pins: A0, A1, A2, A3

I put a 250 ohm resistor between A0 and A1.
I put a 250 ohm resistor between A2 and A3.

I put A0 high and A1 low.
I put A2 high and A3 low.

So I'll have 20 mA flowing from A0 to A1, and another 20 mA flowing from 
A2 to A3.

I don't violate the 25 mA limit for an individual pin, so that's all good.

What I'm interested in though is the total limit for all pins -- I can't 
exceed 90 mA.

I don't understand how the overall limit works though. Is there two 
overall limits, one for sourcing and one for sinking? Is it OK to source 
80 mA from 8 pins while I simultaneously sink 80 mA into a different 8 pins?

In my own example above, how much of the overall limit have I used? Have 
I used 80 mA of an overall 90 mA limit? Or have I used 40 mA of the 
sourcing 90 mA limit, and 40 mA of sinking 90 mA limit?




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