For operation from the Pi, the sequence for reading from the 6522 is as
follows:


 --Note: D'/A output always Low when used with the Pi (connected direct to GND)


A *Pi sets LATCH EN Low.
B *Pi sets Data I/O lines to input mode.
C *Pi sets R/W' output High.
D *Pi sets other Address outputs.
E *When OE' High, Pi sets LATCH EN High (address and data is latched by
   buffer ICs IC1 and IC2).
F *Data is valid after OE' input goes Low to High (and after that until
   interface is disabled). Pi reads Data.
G *Pi sets LATCH EN Low to disable interface.



For Writing:


 --Note: D'/A output always Low when used with the Pi (connected direct to GND)


A *Pi sets LATCH EN Low.
B *Pi sets R/W' output Low.
C *Pi sets other Address outputs, and Data outputs.
D *Pi sets LATCH EN High (address and data is latched by buffer ICs IC1
   and IC2).
E *Data has been written after OE' input goes Low to High (and will
   be again until interface is disabled).
F *Pi sets LATCH EN Low to disable interface.