missing bits from port 2

Peter Borenstein

Why does port 2 only go from [0:4] when we have an 8 bit processor and ports 0 and 1 are [0:7]?

My assumption is that they are sacrificed to create the banked memory model that compensates for the 8051 tiny 16 bit address line.

over 11 years ago

0 _mk over 11 years ago

TI__Expert 4565 points

Hey Peter,

I think it's still an 8 bit register but the top 3 bits aren't used since there are only 5 GPIO for port 2.

-Matt

0 Peter Borenstein over 11 years ago in reply to _mk

Mastermind 8695 points

Right. I understand that there are only 5 GPIOs for port 2, but I was wondering why. What are the other 3 bits doing? Are they configured internally as the upper 3 address lines for the banked flash somewhat like this:

0 Greenja over 11 years ago in reply to Peter Borenstein

Guru 22270 points

You could be right. It may also be due to the fact that they wanted a 40 pin QFN package, some Port Pins had to be sacrificed. The QFN tend to be 32, 40, 48 ... pins.

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missing bits from port 2