COL
---
Anode side, senses keys with internal pull-up.

Left to right:

    PTD6
    PTD5
    PTD4
    PTD3
    
    PTA19
    PTA18
    PTA4 NMI
    PTA2
    PTA1
    
    PTE25
    PTE24
    PTE30
    PTE29
    PTE21
    
ROW
----
Cathod side, given strobe with output low.

Top to bottom:

    PTB3
    PTB16
    PTB17
    PTC0
    PTC1