SA-1

Nintendo SA-1 is an enhancement chip made by Nintendo, used in 33 SNES games. The RF5A123 chip is based on the 65c816 processor, the same one used by the main SNES CPU, the RF5A22. With identical architectures to the SNES one, the chip is ideal for games and ROM hacks that would like to use the code from the main CPU, thus not having to learn an additional assembling language.

Features

With the 10.74 MHz base clock speed, which is four times faster compared to the 2.68 MHz base speed from the S-CPU. In addition to that, it includes with additional hardware circuits for data I/O, bitmap manipulation modes and additional arithmetic registers.

• 16-bit 65c816 processor clocked at 10.74 MHz.
• 2 kB fast internal work memory (I-RAM), clocked at 10.74 MHz.
• Multi-processor processing, with parallel operating mode and memory sharing control.
• Large capacity memory, with a total capability of 8 MB of ROM and 256 kB of BW-RAM, both clocked at 5.37 MHz, with ROM having an effective 10.74 MHz speed due of its 16-bit data bus.
• High speed arithmetic hardware of multiplication, division and cumulative sum (multiply with add).
• Bitmap and Character Conversion functions for fast graphics manipulation.
• Custom DMA circuit for fast transfers between ROM, I-RAM and BW-RAM.
• Variable-Length Bit data processing for enhanced algorithms such as graphics and data compression.
• Super MMC memory mapping capabilities for BW-RAM and bank switching for multiple ROM image access and mirroring.

ROM Hacking

SA-1 Root and SA-1 Pack are known patches used for enabling SA-1 on SNES games that didn't include the chip previously and had problems with slowdown, such as Super Mario World and Gradius III.

Technical Information

Hardware Registers

Register Summary

Write Registers

Address	Length	Code	Access	Description
$2200	1 byte	CCNT	SNES	SA-1 CPU CONTROL
$2201	1 byte	SIE	SNES	SUPER NES CPU INT ENABLE
$2202	1 byte	SIC	SNES	SUPER NES CPU INT CLEAR
$2203	2 bytes	CRV	SNES	SA-1 CPU RESET VECTOR
$2205	2 bytes	CNV	SNES	SA-1 CPU NMI VECTOR
$2207	2 bytes	CIV	SNES	SA-1 CPU IRQ VECTOR
$2209	1 byte	SCNT	SA-1	SUPER NES CPU CONTROL
$220A	1 byte	CIE	SA-1	SA-1 CPU INT ENABLE
$220B	1 byte	CIC	SA-1	SA-1 CPU INT CLEAR
$220C	2 bytes	SNV	SA-1	SUPER NES CPU NMI VECTOR
$220E	2 bytes	SIV	SA-1	SUPER NES CPU IRQ VECTOR
$2210	1 byte	TMC	SA-1	H/V TIMER CONTROL
$2211	1 byte	CTR	SA-1	SA-1 CPU TIMER RESTART
$2212	2 bytes	HCNT	SA-1	SET H-COUNT
$2214	2 bytes	VCNT	SA-1	SET V-COUNT
$2220	1 byte	CXB	SNES	SET SUPER MMC BANK C
$2221	1 byte	DXB	SNES	SET SUPER MMC BANK D
$2222	1 byte	EXB	SNES	SET SUPER MMC BANK E
$2223	1 byte	FXB	SNES	SET SUPER MMC BANK F
$2224	1 byte	BMAPS	SNES	SUPER NES CPU BW-RAM ADDRESS MAPPING
$2225	1 byte	BMAP	SA-1	SA-1 CPU BW-RAM ADDRESS MAPPING
$2226	1 byte	SBWE	SNES	SUPER NES CPU BW-RAM WRITE ENABLE
$2227	1 byte	CBWE	SA-1	SA-1 CPU BW-RAM WRITE ENABLE
$2228	1 byte	BPWA	SNES	BW-RAM WRITE-PROTECTED AREA
$2229	1 byte	SIWP	SNES	SA-1 I-RAM WRITE PROTECTION
$222A	1 byte	CIWP	SA-1	SA-1 I-RAM WRITE PROTECTION
$2230	1 byte	DCNT	SA-1	DMA CONTROL
$2231	1 byte	CDMA	Both	CHARACTER CONVERSION OMA PARAMETERS
$2232	3 bytes	SDA	Both	DMA SOURCE DEVICE START ADDRESS
$2235	3 bytes	DDA	Both	DMA DESTINATION START ADDRESS
$2238	2 bytes	DTC	SA-1	DMA TERMINAL COUNTER
$223F	1 byte	BBF	SA-1	BW-RAM BIT MAP FORMAT
$2240	16 bytes	BRF	SA-1	BIT MAP REGISTER FILE
$2250	1 byte	MCNT	SA-1	ARITHMETIC CONTROL
$2251	2 bytes	MA	SA-1	ARITHMETIC PARAMETERS: MULTIPLICAND/DIVIDEND
$2253	2 bytes	MB	SA-1	ARITHMETIC PARAMETERS: MULTIPLIER/DIVISOR
$2258	1 byte	VBD	SA-1	VARIABLE-LENGTH BIT PROCESSING
$2259	3 bytes	VDA	SA-1	VARIABLE-LENGTH BIT GAME PAK ROM START ADDRESS

Read Registers

Address	Length	Code	Access	Description
$2300	1 bytes	SFR	SNES	SUPER NES CPU FLAG READ
$2301	1 bytes	CFR	SA-1	SA-1 CPU FLAG READ
$2302	2 bytes	HCR	SA-1	H-COUNT READ
$2304	2 bytes	VCR	SA-1	V-COUNT READ
$2306	5 bytes	MR	SA-1	ARITHMETIC RESULT [PRODUCT/QUOTIENT/ACCUMULATIVE SUM]
$230B	1 bytes	OF	SA-1	ARITHMETIC OVERFLOW FLAG
$230C	2 bytes	VDP	SA-1	VARIABLE-LENGTH DATA READ PORT
$230E	1 byte	VC	SNES	VERSION CODE REGISTER (OPEN BUS)

Register Details

$230E - VERSION CODE REGISTER (OPEN BUS)

D7	D6	D5	D4	D3	D2	D1	D0	Register
VC7	VC6	VC5	VC4	VC3	VC2	VC1	VC0	$230E

Bits	Meaning
VC0 ~ VC7	SA-1 Device Version

According the SNES Development Book II, this register was supposed to hold the SA-1 chip version code, however tests made on some real carts has shown that this register in particular is actually open bus.