_____             __   _____             
 / ____|  /\       /_ | |  __ \            
| (___   /  \ ______| | | |  | | ___   ___ 
 \___ \ / /\ \______| | | |  | |/ _ \ / __|
 ____) / ____ \     | | | |__| | (_) | (__ 
|_____/_/    \_\    |_| |_____/ \___/ \___|
     Version 0.20        by Vitor Vilela

This is a work in progress document.

Date: 2019-04-21 (April 21, 2019)

Presentation

This document is a result from many years researchment and testing. I'm continously updating this document with more information and experiments. The information here is accurate but may be subject to revision.

There is not much information available on how the SA-1 chip works, other than the official Nintendo docs which does not very explain much the chip in details but rather focuses on the functionalities and features available. Therefore there is not much information available over undefined behavior or design details. This document attempts in covering it.

If you find any potential issue and/or have any question about this document, feel free to contact me or contribute though GitHub at https://github.com/VitorVilela7/SNES-SA-1-doc/

Memory Map

S-CPU Side

Banks $00-$3F; $80-$BF

• $2200-$23FF : with exception of $2300, all open bus when reading. $2200-$22FF are write-only registers.
• $3000-$37FF : I-RAM
• $6000-$7FFF : BW-RAM Mirror
• $8000-$FFFF : ROM ($00-$1F: CXB, $20-$3F: DXB, $80-$9F: EXB, $A0-$BF: FXB)

Banks $40-$4F : BW-RAM

• The SA-1 chip has enough pins for mapping 256 KB (256 * 1024 bytes) of BW-RAM. The rest is mirror.

Banks $C0-$CF : ROM (CXB)

Banks $D0-$DF : ROM (DXB)

Banks $E0-$EF : ROM (EXB)

Banks $F0-$FF : ROM (FXB)

SA-1 Side

Banks $00-$3F; $80-$BF

• $2200-$23FF : with exception of $2300, all open bus when reading. $2200-$22FF are write-only registers.
• $3000-$37FF : I-RAM
• $6000-$7FFF : BW-RAM Mirror
• $8000-$FFFF : ROM ($00-$1F: CXB, $20-$3F: DXB, $80-$9F: EXB, $A0-$BF: FXB)

Banks $40-$5F : BW-RAM

• The SA-1 chip has enough pins for mapping 256 KB (256 * 1024 bytes) of BW-RAM. The rest is mirror.

Banks $60-$7F : BW-RAM Virtual Memory

• Allows for packing and unpacking BW-RAM by two or four bits (register $223F)
• Allows mapping up to 1 MB (4 bit mode) or 512 KB (2 bit mode)

Banks $C0-$CF : ROM (CXB)

Banks $D0-$DF : ROM (DXB)

Banks $E0-$EF : ROM (EXB)

Banks $F0-$FF : ROM (FXB)

ROM

• Data bus: 16-bit
• Max size: 64 Mbit (8 MB)
• Base speed: 5.37 MHz

I-RAM

Bultin SA-1 RAM chip.

• Data bus: unknown, probably 8-bit.
• Max size: 16 kbit (2 kB)
• Base speed: 10.74 MHz

BW-RAM

Static memory.

• Data bus: 8-bit
• Max size: 2 Mbit (256 KB)
• Base speed: 5.37 MHz

Schematics and pin-outs

This is the schematic of the SA-1 cart, based on the SHVC-1L8B-10 board using a customized EPROM board for custom programming. Most of the information here is not complete, however verified with oscilloscope and with a custom ROM for making sure the descriptions are correct.

I have tracked some of the capacitors and resistors as well, however since it is not the main focus of the research nor I have the proper tools for testing them, they are not complete nor accurate and are listed because they had something to do with some of the main pins.

SRAM

CXK581000AM-70LL (SONY)

Orientation: "ball marking" (left->right)

Pin number	Connection	Pin name	Note
--	--	--	South side
1	CHIP.104	SRAM.NC	SRAM.A17 on CXK582000 @ 256 KB
2	CHIP.86	SRAM.A16
3	CHIP.87	SRAM.A14
4	CHIP.88	SRAM.A12
5	CHIP.89	SRAM.A7
6	CHIP.90	SRAM.A6
7	CHIP.91	SRAM.A5
8	CHIP.92	SRAM.A4
9	CHIP.93	SRAM.A3
10	CHIP.94	SRAM.A2
11	CHIP.95	SRAM.A1
12	CHIP.96	SRAM.A0
13	CHIP.117	SRAM.D0
14	CHIP.116	SRAM.D1
15	CHIP.115	SRAM.D2
16	GND	SRAM.GND
--	--	--	North side
17	CHIP.114	SRAM.D3
18	CHIP.113	SRAM.D4
19	CHIP.112	SRAM.D5
20	CHIP.111	SRAM.D6
21	CHIP.110	SRAM.D7
22	MM1026	SRAM.CE1_N	MM1026 is a circuit responsible for protecting SRAM data and switching power source when needed.
23	CHIP.97	SRAM.A10
24	CHIP.108	SRAM.OE_N
25	CHIP.98	SRAM.A11
26	CHIP.99	SRAM.A9
27	CHIP.102	SRAM.A8
28	CHIP.103	SRAM.A13
29	CHIP.109	SRAM.WE_N
30	WEAK_VBA	SRAM.CE2	Seems to pass though some resistors and MM1026.
31	CHIP.105	SRAM.A15
32	VBA	SRAM.VCC	+3V from battery.

ROM

M27C322 EPROM (ST)

Pin number	Connection	Pin name
--	--	--	South side
1	CHIP.77	ROM.A18
2	CHIP.76	ROM.A17
3	CHIP.66	ROM.A7
4	CHIP.65	ROM.A6
5	CHIP.64	ROM.A5
6	CHIP.63	ROM.A4
7	CHIP.62	ROM.A3
8	CHIP.61	ROM.A2
9	CHIP.60	ROM.A1
10	CHIP.59	ROM.A0
11	GND	ROM.EN_N
12	GND	ROM.GND
13	GND	ROM.PRG
14	CHIP.58	ROM.Q0
15	CHIP.57	ROM.Q8
16	CHIP.56	ROM.Q1
17	CHIP.55	ROM.Q9
18	CHIP.54	ROM.Q2
19	CHIP.53	ROM.Q10
20	CHIP.52	ROM.Q3
21	CHIP.51	ROM.Q11
--	--	--	North side
22	VCC	ROM.VCC
23	CHIP.50	ROM.Q4
24	CHIP.49	ROM.Q12
25	CHIP.48	ROM.Q5
26	CHIP.47	ROM.Q13
27	CHIP.46	ROM.Q6
28	CHIP.45	ROM.Q14
29	CHIP.44	ROM.Q7
30	CHIP.43	ROM.Q15
31	GND	ROM.GND
32	CHIP.79	ROM.A20
33	CHIP.75	ROM.A16
34	CHIP.74	ROM.A15
35	CHIP.73	ROM.A14
36	CHIP.72	ROM.A13
37	CHIP.71	ROM.A12
38	CHIP.70	ROM.A11
39	CHIP.69	ROM.A10
40	CHIP.68	ROM.A9
41	CHIP.67	ROM.A8
42	CHIP.78	ROM.A19

SA-1 cart

Pin number	Connection	Pin name
1	C12+	21477_CLK
2	OPEN	EXPAND
3	OPEN	PA6
4	OPEN	/PARD
--	--	--
5	GND	GND
6	CHIP.35	A11
7	CHIP.33	A10
8	CHIP.31	A9
9	CHIP.29	A8
10	CHIP.27	A7
11	CHIP.25	A6
12	CHIP.23	A5
13	CHIP.21	A4
14	CHIP.19	A3
15	CHIP.17	A2
16	CHIP.15	A1
17	CHIP.13	A0
18	CHIP.1	/IRQ
19	CHIP.9	D0
20	CHIP.7	D1
21	CHIP.5	D2
22	CHIP.3	D3
23	R6->CHIP.128	/RD
24	CHIP.125	CIC_OUT_1
25	CHIP.123	CIC_IN
26	CHIP.120	/RESET
27	VCC	VCC
--	--	--
28	OPEN	PA0
29	OPEN	PA2
30	OPEN	PA4
31	OPEN	AUDIO_L
==	==	==
62	OPEN	AUDIO_R
61	OPEN	PA5
60	OPEN	PA3
59	OPEN	PA1
--	--	--
58	VCC	VCC
57	CHIP.121	CPU_CLK
56	R5->CHIP.122	CIC_CLK
55	CHIP.124	CIC_OUT_2
54	CHIP.126	WR_N
53	CHIP.2	D7
52	CHIP.4	D6
51	CHIP.6	D5
50	CHIP.8	D4
49	OPEN	CART_N
48	CHIP.12	A23
47	CHIP.14	A22
46	CHIP.16	A21
45	CHIP.18	A20
44	CHIP.20	A19
43	CHIP.22	A18
42	CHIP.24	A17
41	CHIP.26	A16
40	CHIP.28	A15
39	CHIP.30	A14
38	CHIP.32	A13
37	CHIP.34	A12
36	GND	GND
--	--	--
35	OPEN	PAWR_N
34	OPEN	PA7
33	CHIP.38, C14	REFRESH
32	OPEN	WRAM_N

SA-1 chip

RF5A123 (NINTENDO)

38:26 pin ratio, total 128 pins.

Number	Connection	Description	Note
--	--	--	South side
1	CART.18	IRQ_N
2	CART.53	D7
3	CART.22	D3
4	CART.52	D6
5	CART.21	D2
6	CART.51	D5
7	CART.20	D1
8	CART.50	D4
9	CART.19	D0
10	C7+	?
11	C7- // GND	?
12	CART.48	A23
13	CART.17	A0
14	CART.47	A22
15	CART.16	A1
16	CART.46	A21
17	CART.15	A2
18	CART.45	A20
19	CART.14	A3
20	CART.44	A19
21	CART.13	A4
22	CART.43	A18
23	CART.12	A5
24	CART.42	A17
25	CART.11	A6
26	CART.41	A16
27	CART.10	A7
28	CART.40	A15
29	CART.9	A8
30	CART.39	A14
31	CART.8	A9
32	CART.38	A13
33	CART.7	A10
34	CART.37	A12
35	CART.6	A11
36	C8+	VCC
37	C8-	GND
38	CART.33	C14+	REFRESH
--	--	--	East side
39	GND
40	R3-	?	Goes though master clock.
41	R2-	?	Goes though master clock.
42	GND
43	ROM.Q15
44	ROM.Q7
45	ROM.Q14
46	ROM.Q6
47	ROM.Q13
48	ROM.Q5
49	ROM.Q12
50	ROM.Q4
51	ROM.Q11
52	ROM.Q3
53	ROM.Q10
54	ROM.Q2
55	ROM.Q9
56	ROM.Q1
57	ROM.Q8
58	ROM.Q0
59	ROM.A0
60	ROM.A1
61	ROM.A2
62	ROM.A3
63	ROM.A4
64	ROM.A5
--	--	--	North side
65	ROM.A6
66	ROM.A7
67	ROM.A8
68	ROM.A9
69	ROM.A10
70	ROM.A11
71	ROM.A12
72	ROM.A13
73	ROM.A14
74	ROM.A15
75	ROM.A16
76	ROM.A17
77	ROM.A18
78	ROM.A19
79	ROM.A20
80	ROM.A21	Unused on this cart.	Pin for 8 MB ROMs.
81	OPEN	?	Always gives VCC apparently.
82	OPEN	?	Looks GND? I had trouble here because it was too close to VCC.
83	VCC
84	GND
85	GND	?	Some boards apparently has it OPEN instead.
86	SRAM.A16
87	SRAM.A14
88	SRAM.A12
89	SRAM.A7
90	SRAM.A6
91	SRAM.A5
92	SRAM.A4
93	SRAM.A3
94	SRAM.A2
95	SRAM.A1
96	SRAM.A0
97	SRAM.A10
98	SRAM.A11
99	SRAM.A9
100	C6+	?
101	C6-	?
102	SRAM.A8
--	--	--	West side
103	SRAM.A13
104	SRAM.A17	$42-$43	Extra SRAM pin for 256KB boards.
105	SRAM.A15
106	SA-1 CLK	Always 10.74 MHz	VCC +5V square wave derived from PPU.
107	SNES CLK	2.68 or 3.58 MHZ	VCC +5V square wave derived from PPU.
108	SRAM.OE_N
109	SRAM.WE_N
110	SRAM.D7
111	SRAM.D6
112	SRAM.D5
113	SRAM.D4
114	SRAM.D3
115	SRAM.D2
116	SRAM.D1
117	SRAM.D0
118	C10-
119	C10+
120	CART.26	RESET_N
121	CART.57	CPU_CLK
122	R5->CART.56	CIC_CLK	Passes though R5.
123	CART.25	CIC_IN
124	CART.55	CIC_OUT_2
125	CART.24	CIC_OUT_1
126	CART.54	WR_N
127	NTSC_N	GND	According nocash, this is NTSC/PAL select pin.
128	R8->CART.23	RD_N	Passes though R8.

Battery

CR2032

• VBA

• GND

Capacitors

Number	+	-	Note
C7	CHIP.10	CHIP.11 // GND
C8	CHIP.37	GND
C9	VCC	GND
C12	CART.1	R3 // C13+	21.477 MHz clock.
C14	CART.33	CHIP.38	REFRESH @ 2.68 MHz

Resistors

Number	Estimated Resistance	+	-
R2	~460k ohm	R3	CHIP.41
R3	~1k ohm	C13-	CHIP.40
R6	~230 ohm	?	?