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SA-1
From SnesLab
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) |