Core repositories here: https://github.com/MiSTer-DB9?tab=repositories

Script for download: https://github.com/theypsilon/Update_All_MiSTer/releases/latest/download/update_all_db9_snac8.zip

USER_IO	DE10	DB9	FPGA	USB3
		8		4 GND
		5		1 5V
0	Arduino_IO15	7	AG11	3 D+
1	Arduino_IO14	3	AH9	2 D-
2	Arduino_IO13	4	AH12	8 TX-
3	Arduino_IO12	6	AH11	7 GND_D
4	Arduino_IO11	shield	AG16	6 RX+
5	Arduino_IO10	1	AF15	5 RX-
6	Arduino_IO8	9	AF17	9 TX+
	Arduino_IO9	2	AE15

9 TX+ is AF17 on SNAC+, with regular SNAC is 3.3V

The second user IO is from Arduino_IO0 to Arduino_IO7 like this diagram.

Genesis	SNES Option 1
A	Y
B	B
C	A
X	L
Y	X
Z	R
START	START
MODE	SELECT

Genesis	SNES Option 2
A	B
B	A
C	R
X	Y
Y	X
Z	L
START	START
MODE	SELECT

Genesis	GBA Option 1
A	B
B	A
C	R
X	FAST FORWARD
Y	L
Z	REWIND
START	START
MODE	SELECT

Genesis	GBA Option 2
A	B
B	A
C	R
X	FAST FORWARD
Y	REWIND
Z	L
START	START
MODE	SELECT

Genesis	Neo Geo
A	A
B	B
C	C
X	SELECT
Y	ABC
Z	D
START	START
MODE	COIN

Genesis	NES Option 1
B	B
C	A
START	START
MODE	SELECT

Genesis	NES Option 2
B	A
C	B
START	START
MODE	SELECT

Genesis	Master System
B	1
C	2
START	START/PAUSE

Genesis	TurboGrafx
A	III
B	II
C	I
X	IV
Y	V
Z	VI
START	RUN
MODE	SELECT

Genesis	Atari 2600
B	A
START	START
MODE	SELECT

Genesis	GB/GBC
B	A
C	B
START	START
MODE	SELECT
A	SELECT

Genesis	Generic Arcade
A	Button 1 (Fire)
B	Button 2 (Jump)
C	Button 3
X	Button 4
Y	Button 5
Z	Button 6
START	START
MODE	COIN
START+B	COIN
START+C	OSD