Possible Duplicate:
Why are the pinouts of lpc21xx all over the place?
I have often noticed, and found it quite annoying from a PCB layout point of view, just how illogical many IC's pinouts are.
Let me give you an example:
They've done a good job with port B. Port A is almost there - A6 and A7 seem to have wandered off a little... But what is with ports C and D?
Another example - the Z80's data bus:
I mean, that one just makes no sense to me whatsoever. Not only are then in some seemingly random order, but you suddenly get +5V in the middle.
So what is the reason for this? Are they doing it just to be annoying, or is there some sound technical reason why the pins have to be in these strange orders?
