Use the SNES/NES controller in Assembly

NES and SNES controllers

The F256 machines can use these controllers provided they are equipped with an optional FNX4N4S breakout adapter.

The official gamepads of yesteryear work without issue with this and are plentiful in the used market.

Third party modern recreations are sometimes flaky or not working at all. Share you discoveries in the discord!

Super famicom gamepads work very well as substitute for regular SNES gamepads.

Registers

Register Name	R/W	Address	NES/SNES	Description
PAD_CTRL	W	0xD880	both	Used to trigger a reading and setting the NES/SNES mode
PAD_STAT	R	0xD880	both	Used to verify if the triggered polling of gamepad state is done yet
PAD0	R	0xD884	both	Buttons statuses: if cleared, they are pressed. If set, they are unpressed.
PAD0_S	R	0xD885	SNES	Same deal; unused by NES. Consult button table below
PAD1	R	0xD886	both	Buttons statuses: if cleared, they are pressed. If set, they are unpressed.
PAD1_S	R	0xD887	SNES	Same deal; unused by NES. Consult button table below
PAD2	R	0xD888	both	Buttons statuses: if cleared, they are pressed. If set, they are unpressed.
PAD2_S	R	0xD889	SNES	Same deal; unused by NES. Consult button table below
PAD3	R	0xD88A	both	Buttons statuses: if cleared, they are pressed. If set, they are unpressed.
PAD3_S	R	0xD88B	SNES	Same deal; unused by NES. Consult button table below

Control register

Register Name	R/W	Address	Bit7	Bit6	Bit5	Bit4	Bit3	Bit2	Bit1	Bit0
PAD_CTRL	W	0xD880	NES_TRIG	-	-	-	-	MODE	-	EN
PAD_STAT	R	0xD880	NES_TRIG	DONE	-	-	-	MODE	-	EN

Control register bit states:

Bit Name	If set to 1	If cleared to 0
NES_TRIG	Launches the polling of the states of all buttons	Stops polling the states of all buttons
DONE	The states of the buttons are ready to be read	The states of the buttons are not ready
MODE	SNES data will be used to populate the PAD registers	NES data will be used to populate the PAD registers
EN	Enables the gamepads	Disables the gamepads

Button table

MODE	NES/SNES	Address	Pad	Bit7	Bit6	Bit5	Bit4	Bit3	Bit2	Bit1	Bit0
0	NES	0xD884	0	A	B	Select	Start	Up	Down	Left	Right
0	NES	0xD886	1	A	B	Select	Start	Up	Down	Left	Right
0	NES	0xD888	2	A	B	Select	Start	Up	Down	Left	Right
0	NES	0xD88A	3	A	B	Select	Start	Up	Down	Left	Right
1	SNES	0xD884	0	B	Y	Select	Start	Up	Down	Left	Right
1	SNES	0xD885	0					A	X	L	R
1	SNES	0xD886	1	B	Y	Select	Start	Up	Down	Left	Right
1	SNES	0xD887	1					A	X	L	R
1	SNES	0xD888	2	B	Y	Select	Start	Up	Down	Left	Right
1	SNES	0xD889	2					A	X	L	R
1	SNES	0xD88A	3	B	Y	Select	Start	Up	Down	Left	Right
1	SNES	0xD88B	3					A	X	L	R

Note: L refers to the left shoulder button and R refers to the right shoulder button.

Usage

Example 1: polling a NES controller in PAD0 position and checking if A is pressed:

POKE(PAD_CTRL, 0b10000001); //trigger, nes mode, enabled
while((PEEK(PAD_STAT) & 0x40) == 0) //loop while this bit is cleared
      ;
if((PEEK(PAD0) & 0x80) == 0) reactToAPressed();
POKE(PAD_CTRL, 0b00000001); //clear trigger

Example 2: polling a SNES controller in PAD2 position and checking if X is pressed:

POKE(PAD_CTRL, 0b10000101); //trigger, snes mode, enabled
while((PEEK(PAD_STAT) & 0x40) == 0) //loop while this bit is cleared

     ;

if((PEEK(PAD2_S) & 0x04) == 0) reactToXPressed();
POKE(PAD_CTRL, 0b00000101); //clear trigger

Example 3: polling both types of controller in rapid succession (allows the usage of all 8 controllers!)

//NES section
POKE(PAD_CTRL, 0b10000001); //trigger, nes mode, enabled
while((PEEK(PAD_STAT) & 0x40) == 0) //loop while this bit is cleared

     ;

//section where reactions are made to the various NES presses
POKE(PAD_CTRL, 0b00000001); //clear trigger
POKE(PAD_CTRL, 0b10000101); //trigger, snes mode, enabled
while((PEEK(PAD_STAT) & 0x40) == 0) //loop while this bit is cleared

     ;

//section where reactions are made to the various SNES presses
POKE(PAD_CTRL, 0b00000101); //clear trigger