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Programmable I/O Port
From SnesLab
The 8-bit Programmable I/O Port allows the 5A22 to communicate with SNES peripherals.
There is the register commonly referred to as WRIO for short located at 4201h. Only the top two bits are used by the control deck. It has open collector output and is initialized to FFh on reset.[2] WRIO is the out-port. The last sentence of page 2-14-1 likely has a typo; supposed to be referring to page 2-28-1 not 1-28-1.
There is also the RDIO register at 4213h. Only the top two bits are used by the control deck. RDIO is the in-port.
See Also
References
- Official Super Nintendo development manual on the programmable i/o port: Page 2-14-1 of Book I
- https://problemkaputt.de/fullsnes.htm#snescontrollersioportsmanualreading
- page 2-28-1 of Book I on WRIO
- page 2-28-7 of Book I on RDIO