This article describes a direct wiring connection between a standard Sega Dreamcast expansion (G2) port devices (like Modem, Broadband Adapter or LAN adapter) and the CN2 connector on the Sega NAOMI and NAOMI 2 motherboards.
Also included connection mapping for AtomisWave Broadband Adapter.

Dreamcast G2 (CN501) to NAOMI CN2 Signal Mapping

This pinout allows you to connect standard Dreamcast G2 devices to NAOMI.

DC Pin (CN501)	Signal	CN2 Pin
1, 2, 3, 4	5V	A1, B5, B7, B9, B11, B13, B15, B19, B21
5	/G2_MDMCS	A19
6	/G2_IRQMDM	A9
7	/G2_RQDEV	B14
8	/G2_RQEX1	B12
9	/G2_RQEX0	A15
10-12, 23-24, 41-42, 44-45, 47-48	GND	A4, A6, A8, A10, A12, A14, A16, A18, A20, A23, A25, A29, A31, A33, A35, A37, A41, B2, B18, B24, B46, B48, B50
13	/G2_IREXT	A11
14	/G2_BL	B22
15	/G2_ST	B20
16	/G2_BH	A21
17, 18, 19	3.3V	B26, B28, B30, B32, B34, B36, B38, B40, B42, B44, B46, B49
20	/G2_DS	A17
21	/G2_FRAME	B16
22	/G2_TR	B18
25	G2_AD15	B39
26	G2_AD14	A38
27	G2_AD13	B37
28	G2_AD12	A36
29	G2_AD11	B35
30	G2_AD10	A34
31	G2_AD9	B33
32	G2_AD8	A32
33	G2_AD7	B31
34	G2_AD6	A30
35	G2_AD5	B29
36	G2_AD4	A28
37	G2_AD3	B27
38	G2_AD2	A26
39	G2_AD1	B25
40	G2_AD0	A24
43	CLOCK (25MHz)	A7
46	/G_RESET	B3

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AtomisWave BBA to NAOMI CN2 Signal Mapping

Connection mapping for AtomisWave Broadband Adapter.

AW Pin	Signal	CN2 Pin
A4	G2_AD1	B25
A5	G2_AD3	B27
A6	G2_AD5	B29
A7	G2_AD7	B31
A8	G2_AD9	B33
A9	G2_AD11	B35
A10	G2_AD13	B37
A11	G2_AD15	B39
A14	/G2_DS	A17
A15	/G2_BL	B22
A16	/G_RESET	B3
A17	CLOCK	A7
B4	G2_AD0	A24
B5	G2_AD2	A26
B6	G2_AD4	A28
B7	G2_AD6	A30
B8	G2_AD8	A32
B9	G2_AD10	A34
B10	G2_AD12	A36
B11	G2_AD14	A38
B12	/G2_IREXT	A11
B13	/G2_TR	B18
B14	/G2_FRAME	B16
B15	/G2_BH	A21
A1, A2, A3, B1, B2, B3	GND	A20, A23, A16, A18, A12, A14, A8, A10, A4, B42, B44
A22, A23, B22, B23	3.3V	B26, B28, B30, B32, B34, B36, B38, B40

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NAOMI and NAOMI 2 CN2 Connector Pinout

The following table show CN2 pinout for reference.
Pins marked as NC are not connected.

Pin	Signal	Pin	Signal
A1	5V	B1	NC
A2	TO_IC4_PIN13	B2	GND
A3	TO_IC4_PIN10	B3	/G_RESET
A4	GND	B4	?
A5	IC44_PIN4	B5	5V
A6	GND	B6	/SH4_IRL1
A7	CLOCK (25MHz)	B7	5V
A8	GND	B8	NC
A9	/G2_IRMDM	B9	5V
A10	GND	B10	/G2_IRAIC
A11	/G2_IREXT	B11	5V
A12	GND	B12	/G2_RQEX1
A13	/G2_RDAIC	B13	5V
A14	GND	B14	/G2_RQDEV
A15	/G2_RQEX0	B15	5V
A16	GND	B16	/G2_FRAME
A17	/G2_DS	B17	5V
A18	GND	B18	/G2_TR
A19	/G2_MDMCS	B19	5V
A20	GND	B20	/G2_ST
A21	/G2_BH	B21	5V
A22	NC	B22	/G2_BL
A23	GND	B23	NC
A24	G2_AD0	B24	5V
A25	GND	B25	G2_AD1
A26	G2_AD2	B26	3V3
A27	GND	B27	G2_AD3
A28	G2_AD4	B28	3V3
A29	GND	B29	G2_AD5
A30	G2_AD6	B30	3V3
A31	GND	B31	G2_AD7
A32	G2_AD8	B32	3V3
A33	GND	B33	G2_AD9
A34	G2_AD10	B34	3V3
A35	GND	B35	G2_AD11
A36	G2_AD12	B36	3V3
A37	GND	B37	G2_AD13
A38	G2_AD14	B38	3V3
A39	GND	B39	G2_AD15
A40	TORX_195 (To LINK Tx)	B40	3V3
A41	GND	B41	TORX_194 (From LINK Rx)
A42	CD_SD	B42	3V3
A43	GND	B43	CD_BCK
A44	CD_LRCK	B44	3V3
A45	GND	B45	IC36_PIN12
A46	NC	B46	3V3
A47	GND	B47	NC
A48	JP1_PIN1	B48	Analog Ground
A49	GND	B49	Audio to IC39
A50	Audio to IC39	B50	Analog Ground