Memory Management
The F256 line comes with 512 KB of RAM and 512 KB of flash memory. Up to 256 KB additional Memory, either RAM or Flash, can be added through the Expansion Port.
Physical Memory Layout
The address bus is 21 bits wide, allowing a total of 221 = 2 MB to be addressed.
| Address | Purpose |
|---|---|
| $00:0000 - $07:FFFF | RAM |
| $08:0000 - $0F:FFFF | Flash |
| $10:0000 - $13:FFFF | Expansion Memory |
| $14:0000 - $1F:FFFF | Reserved |
Memory Management Unit (MMU)
While the address bus is generally 21 bits wide, the CPU address bus of the 65c02 and the FNX6809 is only 16 bits wide. Even though the 65816 does have a 24 bit wide address bus, it is currently not used in the classic 6502 MMU core. However, this is now possible with the extended memory map of the 2x speed 65816. These changes have been added in the summer of 2025 and are marked in italics and underlined in the following tables.
To allow the addressing of the whole address space, 4 Memory Management Units (MMU) are provided, that translate the CPU logical address space to physical addresses.
To achieve this, each MMU has 8 slots, each representing an 8 KB block of the CPU addressable memory space.
The physical address space is also divided into 8 KB blocks, dividing the available 2 MB into 256 blocks.
To map a block of physical addresses into CPU address space, the block number is written into the according slot register of the MMU.
| Slot | CPU Address Space | Slot Register Address |
|---|---|---|
| 0 | $0000 - $1FFF | $0008 |
| 1 | $2000 - $3FFF | $0009 |
| 2 | $4000 - $5FFF | $000A |
| 3 | $6000 - $7FFF | $000B |
| 4 | $8000 - $9FFF | $000C |
| 5 | $A000 - $BFFF | $000D |
| 6 | $C000 - $DFFF | $000E |
| 7 | $E000 - $FFFF | $000F |
Only one MMU is active at any one time. To select the active MMU, the lower two bits of address $0000 (MMU_MEM_CTRL) are used.
Editing of MMUs is also controlled by MMU_MEM_CTRL ($0000): Bits 4 and 5 determine which set of MMU registers is to be edited, while bit 7 has to be set to 1 to enable editing. When editing is enable, the block number of a physical memory area can be written to the slot register address to map that area to the address in CPU address space. If editing is not enabled (bit 7 of $0000 is 0), the slot register addresses act as ordinary memory with no side effect.
| Address | R/W | Name | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|---|---|---|---|---|---|---|---|---|---|---|
| 0x0000 | RW | MMU_MEM_CTRL | EDIT_EN | - | EDIT_LUT | SRAM_EN | - | ACT_LUT | ||
| 0x0001 | RW | MMU_IO_CTRL | - | SPR_SEL | MOVE_FLASH | MOVE_IO | IO_PAGE_EXT | IO_DISABLE | IO_PAGE | |
ACT_LUT these two bits specify which MLUT (0–3) is used to translate CPU bus address to system
bus addresses.
EDIT_EN if set (1), this bit allows a MLUT to be edited by the program, and memory addresses
0x0008–0x0010 will be used by the MLUT being edited. If clear (0), those memory locations
will be standard memory locations and will be mapped like the rest of bank 0.
EDIT_LUT if EDIT_EN is set, these two bits will specify which MLUT (0 - 3) is being edited and
will appear in memory addresses 0x0008–0x0010.
SRAM_EN (2x speed 65816 core only) enables access to the SRAM in extended mode (24 bit addresses)
IO_DISABLE if set (1), bank 6 is mapped like any other memory bank. If clear (0), bank 6 is
mapped to I/O memory.
IO_PAGE if IO_DISABLE is clear, these two bits specify which bank of I/O memory (0 - 3) is
mapped to bank 6.
IO_PAGE_EXT (2x only)allows to access more io pages (4 and 5)
MOVE_IO (2x only) Moves decoding of IO Devices to High-Memory
MOVE_FLASH (2x only) Moves decoding of Flash/Cart to High-Memory
SPR_SEL (2x only) Sprite Block Select - 0: Sprite 0-63, 1: Sprite 64-127
| I/O Bank | B3 | B1 | B0 | Purpose |
|---|---|---|---|---|
| 0 | 0 | 0 | 0 | Low level I/O Register (gamma table, Mouse GFX, all IO devices and vicky registers) |
| 1 | 0 | 0 | 1 | Text display font memory and graphic color MLUTs 0,1,2,3 |
| 2 | 0 | 1 | 0 | Text display character matrix |
| 3 | 0 | 1 | 1 | Text display color matrix |
| 4 | 1 | 0 | 0 | Memory text Color background LUT 0 & 1, Foreground LUT 0 & 1 |
| 5 | 1 | 0 | 1 | Memory text FONT 0,1,2,3 for 8x8 or 0,1 for 8x16 |
| 6 | 1 | 1 | 0 | unused |
| 7 | 1 | 1 | 1 | unused |
Memory Block Tables
Overview of the block tables, including the new RAM locations addressed by the 2x speed 65816 extended map core:
| Range | Description |
|---|---|
| $00_0000 to $07_FFFF | 512K SRAM Default RAM (Page 0) |
| $08_0000 to $0F_0000 | 512K FLASH |
| $10_0000 to $13_FFFF | 256K Cartridge |
| $14_000 to $1F_FFFF | 768K Nothing Here |
| $20_000 to $27_FFFF | 512K SRAM Page 1 |
| $40_000 to $47_FFFF | 512K SRAM Page 2 |
| $60_000 to $67_FFFF | 512K SRAM Page 3 |
The following table shows which block number has to be written into a slot register to make the each 8 KB block of memory available to the CPU.
| RAM | Flash | Expansion | |||||
|---|---|---|---|---|---|---|---|
| Block Number | Physical Address | Block Number | Physical Address | Block Number | Physical Address | ||
| $00 | $00:0000 - $00:1FFF | $40 | $08:0000 - $08:1FFF | $80 | $10:0000 - $10:1FFF | ||
| $01 | $00:2000 - $00:3FFF | $41 | $08:2000 - $08:3FFF | $81 | $10:2000 - $10:3FFF | ||
| $02 | $00:4000 - $00:5FFF | $42 | $08:4000 - $08:5FFF | $82 | $10:4000 - $10:5FFF | ||
| $03 | $00:6000 - $00:7FFF | $43 | $08:6000 - $08:7FFF | $83 | $10:6000 - $10:7FFF | ||
| $04 | $00:8000 - $00:9FFF | $44 | $08:8000 - $08:9FFF | $84 | $10:8000 - $10:9FFF | ||
| $05 | $00:A000 - $00:BFFF | $45 | $08:A000 - $08:BFFF | $85 | $10:A000 - $10:BFFF | ||
| $06 | $00:C000 - $00:DFFF | $46 | $08:C000 - $08:DFFF | $86 | $10:C000 - $10:DFFF | ||
| $07 | $00:E000 - $00:FFFF | $47 | $08:E000 - $08:FFFF | $87 | $10:E000 - $10:FFFF | ||
| $08 | $01:0000 - $01:1FFF | $48 | $09:0000 - $09:1FFF | $88 | $11:0000 - $11:1FFF | ||
| $09 | $01:2000 - $01:3FFF | $49 | $09:2000 - $09:3FFF | $89 | $11:2000 - $11:3FFF | ||
| $0A | $01:4000 - $01:5FFF | $4A | $09:4000 - $09:5FFF | $8A | $11:4000 - $11:5FFF | ||
| $0B | $01:6000 - $01:7FFF | $4B | $09:6000 - $09:7FFF | $8B | $11:6000 - $11:7FFF | ||
| $0C | $01:8000 - $01:9FFF | $4C | $09:8000 - $09:9FFF | $8C | $11:8000 - $11:9FFF | ||
| $0D | $01:A000 - $01:BFFF | $4D | $09:A000 - $09:BFFF | $8D | $11:A000 - $11:BFFF | ||
| $0E | $01:C000 - $01:DFFF | $4E | $09:C000 - $09:DFFF | $8E | $11:C000 - $11:DFFF | ||
| $0F | $01:E000 - $01:FFFF | $4F | $09:E000 - $09:FFFF | $8F | $11:E000 - $11:FFFF | ||
| $10 | $02:0000 - $02:1FFF | $50 | $0A:0000 - $0A:1FFF | $90 | $12:0000 - $12:1FFF | ||
| $11 | $02:2000 - $02:3FFF | $51 | $0A:2000 - $0A:3FFF | $91 | $12:2000 - $12:3FFF | ||
| $12 | $02:4000 - $02:5FFF | $52 | $0A:4000 - $0A:5FFF | $92 | $12:4000 - $12:5FFF | ||
| $13 | $02:6000 - $02:7FFF | $53 | $0A:6000 - $0A:7FFF | $93 | $12:6000 - $12:7FFF | ||
| $14 | $02:8000 - $02:9FFF | $54 | $0A:8000 - $0A:9FFF | $94 | $12:8000 - $12:9FFF | ||
| $15 | $02:A000 - $02:BFFF | $55 | $0A:A000 - $0A:BFFF | $95 | $12:A000 - $12:BFFF | ||
| $16 | $02:C000 - $02:DFFF | $56 | $0A:C000 - $0A:DFFF | $96 | $12:C000 - $12:DFFF | ||
| $17 | $02:E000 - $02:FFFF | $57 | $0A:E000 - $0A:FFFF | $97 | $12:E000 - $12:FFFF | ||
| $18 | $03:0000 - $03:1FFF | $58 | $0B:0000 - $0B:1FFF | $98 | $13:0000 - $13:1FFF | ||
| $19 | $03:2000 - $03:3FFF | $59 | $0B:2000 - $0B:3FFF | $99 | $13:2000 - $13:3FFF | ||
| $1A | $03:4000 - $03:5FFF | $5A | $0B:4000 - $0B:5FFF | $9A | $13:4000 - $13:5FFF | ||
| $1B | $03:6000 - $03:7FFF | $5B | $0B:6000 - $0B:7FFF | $9B | $13:6000 - $13:7FFF | ||
| $1C | $03:8000 - $03:9FFF | $5C | $0B:8000 - $0B:9FFF | $9C | $13:8000 - $13:9FFF | ||
| $1D | $03:A000 - $03:BFFF | $5D | $0B:A000 - $0B:BFFF | $9D | $13:A000 - $13:BFFF | ||
| $1E | $03:C000 - $03:DFFF | $5E | $0B:C000 - $0B:DFFF | $9E | $13:C000 - $13:DFFF | ||
| $1F | $03:E000 - $03:FFFF | $5F | $0B:E000 - $0B:FFFF | $9F | $13:E000 - $13:FFFF | ||
| $20 | $04:0000 - $04:1FFF | $60 | $0C:0000 - $0C:1FFF | ||||
| $21 | $04:2000 - $04:3FFF | $61 | $0C:2000 - $0C:3FFF | ||||
| $22 | $04:4000 - $04:5FFF | $62 | $0C:4000 - $0C:5FFF | ||||
| $23 | $04:6000 - $04:7FFF | $63 | $0C:6000 - $0C:7FFF | ||||
| $24 | $04:8000 - $04:9FFF | $64 | $0C:8000 - $0C:9FFF | ||||
| $25 | $04:A000 - $04:BFFF | $65 | $0C:A000 - $0C:BFFF | ||||
| $26 | $04:C000 - $04:DFFF | $66 | $0C:C000 - $0C:DFFF | ||||
| $27 | $04:E000 - $04:FFFF | $67 | $0C:E000 - $0C:FFFF | ||||
| $28 | $05:0000 - $05:1FFF | $68 | $0D:0000 - $0D:1FFF | ||||
| $29 | $05:2000 - $05:3FFF | $69 | $0D:2000 - $0D:3FFF | ||||
| $2A | $05:4000 - $05:5FFF | $6A | $0D:4000 - $0D:5FFF | ||||
| $2B | $05:6000 - $05:7FFF | $6B | $0D:6000 - $0D:7FFF | ||||
| $2C | $05:8000 - $05:9FFF | $6C | $0D:8000 - $0D:9FFF | ||||
| $2D | $05:A000 - $05:BFFF | $6D | $0D:A000 - $0D:BFFF | ||||
| $2E | $05:C000 - $05:DFFF | $6E | $0D:C000 - $0D:DFFF | ||||
| $2F | $05:E000 - $05:FFFF | $6F | $0D:E000 - $0D:FFFF | ||||
| $30 | $06:0000 - $06:1FFF | $70 | $0E:0000 - $0E:1FFF | ||||
| $31 | $06:2000 - $06:3FFF | $71 | $0E:2000 - $0E:3FFF | ||||
| $32 | $06:4000 - $06:5FFF | $72 | $0E:4000 - $0E:5FFF | ||||
| $33 | $06:6000 - $06:7FFF | $73 | $0E:6000 - $0E:7FFF | ||||
| $34 | $06:8000 - $06:9FFF | $74 | $0E:8000 - $0E:9FFF | ||||
| $35 | $06:A000 - $06:BFFF | $75 | $0E:A000 - $0E:BFFF | ||||
| $36 | $06:C000 - $06:DFFF | $76 | $0E:C000 - $0E:DFFF | ||||
| $37 | $06:E000 - $06:FFFF | $77 | $0E:E000 - $0E:FFFF | ||||
| $38 | $07:0000 - $07:1FFF | $78 | $0F:0000 - $0F:1FFF | ||||
| $39 | $07:2000 - $07:3FFF | $79 | $0F:2000 - $0F:3FFF | ||||
| $3A | $07:4000 - $07:5FFF | $7A | $0F:4000 - $0F:5FFF | ||||
| $3B | $07:6000 - $07:7FFF | $7B | $0F:6000 - $0F:7FFF | ||||
| $3C | $07:8000 - $07:9FFF | $7C | $0F:8000 - $0F:9FFF | ||||
| $3D | $07:A000 - $07:BFFF | $7D | $0F:A000 - $0F:BFFF | ||||
| $3E | $07:C000 - $07:DFFF | $7E | $0F:C000 - $0F:DFFF | ||||
| $3F | $07:E000 - $07:FFFF | $7F | $0F:E000 - $0F:FFFF | ||||
For 2x speed extended map 65816 core:
| 512K SRAM Page 1 | 512K SRAM Page 2 | 512K SRAM Page 3 | |||||
|---|---|---|---|---|---|---|---|
| Block Number | Physical Address | Block Number | Physical Address | Block Number | Physical Address | ||
| $100 | $20:0000 - $20:1FFF | $200 | $40:0000 - $40:1FFF | $300 | $60:0000 - $60:1FFF | ||
| $101 | $20:2000 - $20:3FFF | $201 | $40:2000 - $40:3FFF | $301 | $60:2000 - $60:3FFF | ||
| $102 | $20:4000 - $20:5FFF | $202 | $40:4000 - $40:5FFF | $302 | $60:4000 - $60:5FFF | ||
| $103 | $20:6000 - $20:7FFF | $203 | $40:6000 - $40:7FFF | $303 | $60:6000 - $60:7FFF | ||
| $104 | $20:8000 - $20:9FFF | $204 | $40:8000 - $40:9FFF | $304 | $60:8000 - $60:9FFF | ||
| $105 | $20:A000 - $20:BFFF | $205 | $40:A000 - $40:BFFF | $305 | $60:A000 - $60:BFFF | ||
| $106 | $20:C000 - $20:DFFF | $206 | $40:C000 - $40:DFFF | $306 | $60:C000 - $60:DFFF | ||
| $107 | $20:E000 - $20:FFFF | $207 | $40:E000 - $40:FFFF | $307 | $60:E000 - $60:FFFF | ||
| $108 | $21:0000 - $21:1FFF | $208 | $41:0000 - $41:1FFF | $308 | $61:0000 - $61:1FFF | ||
| $109 | $21:2000 - $21:3FFF | $209 | $41:2000 - $41:3FFF | $309 | $61:2000 - $61:3FFF | ||
| $10A | $21:4000 - $21:5FFF | $20A | $41:4000 - $41:5FFF | $30A | $61:4000 - $61:5FFF | ||
| $10B | $21:6000 - $21:7FFF | $20B | $41:6000 - $41:7FFF | $30B | $61:6000 - $61:7FFF | ||
| $10C | $21:8000 - $21:9FFF | $20C | $41:8000 - $41:9FFF | $30C | $61:8000 - $61:9FFF | ||
| $10D | $21:A000 - $21:BFFF | $20D | $41:A000 - $41:BFFF | $30D | $61:A000 - $61:BFFF | ||
| $10E | $21:C000 - $21:DFFF | $20E | $41:C000 - $41:DFFF | $30E | $61:C000 - $61:DFFF | ||
| $10F | $21:E000 - $21:FFFF | $20F | $41:E000 - $41:FFFF | $30F | $61:E000 - $61:FFFF | ||
| $110 | $22:0000 - $22:1FFF | $210 | $42:0000 - $42:1FFF | $310 | $62:0000 - $62:1FFF | ||
| $111 | $22:2000 - $22:3FFF | $211 | $42:2000 - $42:3FFF | $311 | $62:2000 - $62:3FFF | ||
| $112 | $22:4000 - $22:5FFF | $212 | $42:4000 - $42:5FFF | $312 | $62:4000 - $62:5FFF | ||
| $113 | $22:6000 - $22:7FFF | $213 | $42:6000 - $42:7FFF | $313 | $62:6000 - $62:7FFF | ||
| $114 | $22:8000 - $22:9FFF | $214 | $42:8000 - $42:9FFF | $314 | $62:8000 - $62:9FFF | ||
| $115 | $22:A000 - $22:BFFF | $215 | $42:A000 - $42:BFFF | $315 | $62:A000 - $62:BFFF | ||
| $116 | $22:C000 - $22:DFFF | $216 | $42:C000 - $42:DFFF | $316 | $62:C000 - $62:DFFF | ||
| $117 | $22:E000 - $22:FFFF | $217 | $42:E000 - $42:FFFF | $317 | $62:E000 - $62:FFFF | ||
| $118 | $23:0000 - $23:1FFF | $218 | $43:0000 - $43:1FFF | $318 | $63:0000 - $63:1FFF | ||
| $119 | $23:2000 - $23:3FFF | $219 | $43:2000 - $43:3FFF | $319 | $63:2000 - $63:3FFF | ||
| $11A | $23:4000 - $23:5FFF | $21A | $43:4000 - $43:5FFF | $31A | $63:4000 - $63:5FFF | ||
| $11B | $23:6000 - $23:7FFF | $21B | $43:6000 - $43:7FFF | $31B | $63:6000 - $63:7FFF | ||
| $11C | $23:8000 - $23:9FFF | $21C | $43:8000 - $43:9FFF | $31C | $63:8000 - $63:9FFF | ||
| $11D | $23:A000 - $23:BFFF | $21D | $43:A000 - $43:BFFF | $31D | $63:A000 - $63:BFFF | ||
| $11E | $23:C000 - $23:DFFF | $21E | $43:C000 - $43:DFFF | $31E | $63:C000 - $63:DFFF | ||
| $11F | $23:E000 - $23:FFFF | $21F | $43:E000 - $43:FFFF | $31F | $63:E000 - $63:FFFF | ||
| $120 | $24:0000 - $24:1FFF | $220 | $44:0000 - $44:1FFF | $320 | $64:0000 - $64:1FFF | ||
| $121 | $24:2000 - $24:3FFF | $221 | $44:2000 - $44:3FFF | $321 | $64:2000 - $64:3FFF | ||
| $122 | $24:4000 - $24:5FFF | $222 | $44:4000 - $44:5FFF | $322 | $64:4000 - $64:5FFF | ||
| $123 | $24:6000 - $24:7FFF | $223 | $44:6000 - $44:7FFF | $323 | $64:6000 - $64:7FFF | ||
| $124 | $24:8000 - $24:9FFF | $224 | $44:8000 - $44:9FFF | $324 | $64:8000 - $64:9FFF | ||
| $125 | $24:A000 - $24:BFFF | $225 | $44:A000 - $44:BFFF | $325 | $64:A000 - $64:BFFF | ||
| $126 | $24:C000 - $24:DFFF | $226 | $44:C000 - $44:DFFF | $326 | $64:C000 - $64:DFFF | ||
| $127 | $24:E000 - $24:FFFF | $227 | $44:E000 - $44:FFFF | $327 | $64:E000 - $64:FFFF | ||
| $128 | $25:0000 - $25:1FFF | $228 | $45:0000 - $45:1FFF | $328 | $65:0000 - $65:1FFF | ||
| $129 | $25:2000 - $25:3FFF | $229 | $45:2000 - $45:3FFF | $329 | $65:2000 - $65:3FFF | ||
| $12A | $25:4000 - $25:5FFF | $22A | $45:4000 - $45:5FFF | $32A | $65:4000 - $65:5FFF | ||
| $12B | $25:6000 - $25:7FFF | $22B | $45:6000 - $45:7FFF | $32B | $65:6000 - $65:7FFF | ||
| $12C | $25:8000 - $25:9FFF | $22C | $45:8000 - $45:9FFF | $32C | $65:8000 - $65:9FFF | ||
| $12D | $25:A000 - $25:BFFF | $22D | $45:A000 - $45:BFFF | $32D | $65:A000 - $65:BFFF | ||
| $12E | $25:C000 - $25:DFFF | $22E | $45:C000 - $45:DFFF | $32E | $65:C000 - $65:DFFF | ||
| $12F | $25:E000 - $25:FFFF | $22F | $45:E000 - $45:FFFF | $32F | $65:E000 - $65:FFFF | ||
| $130 | $26:0000 - $26:1FFF | $230 | $46:0000 - $46:1FFF | $330 | $66:0000 - $66:1FFF | ||
| $131 | $26:2000 - $26:3FFF | $231 | $46:2000 - $46:3FFF | $331 | $66:2000 - $66:3FFF | ||
| $132 | $26:4000 - $26:5FFF | $232 | $46:4000 - $46:5FFF | $332 | $66:4000 - $66:5FFF | ||
| $133 | $26:6000 - $26:7FFF | $233 | $46:6000 - $46:7FFF | $333 | $66:6000 - $66:7FFF | ||
| $134 | $26:8000 - $26:9FFF | $234 | $46:8000 - $46:9FFF | $334 | $66:8000 - $66:9FFF | ||
| $135 | $26:A000 - $26:BFFF | $235 | $46:A000 - $46:BFFF | $335 | $66:A000 - $66:BFFF | ||
| $136 | $26:C000 - $26:DFFF | $236 | $46:C000 - $46:DFFF | $336 | $66:C000 - $66:DFFF | ||
| $137 | $26:E000 - $26:FFFF | $237 | $46:E000 - $46:FFFF | $337 | $66:E000 - $66:FFFF | ||
| $138 | $27:0000 - $27:1FFF | $238 | $47:0000 - $47:1FFF | $338 | $67:0000 - $67:1FFF | ||
| $139 | $27:2000 - $27:3FFF | $239 | $47:2000 - $47:3FFF | $339 | $67:2000 - $67:3FFF | ||
| $13A | $27:4000 - $27:5FFF | $23A | $47:4000 - $47:5FFF | $33A | $67:4000 - $67:5FFF | ||
| $13B | $27:6000 - $27:7FFF | $23B | $47:6000 - $47:7FFF | $33B | $67:6000 - $67:7FFF | ||
| $13C | $27:8000 - $27:9FFF | $23C | $47:8000 - $47:9FFF | $33C | $67:8000 - $67:9FFF | ||
| $13D | $27:A000 - $27:BFFF | $23D | $47:A000 - $47:BFFF | $33D | $67:A000 - $67:BFFF | ||
| $13E | $27:C000 - $27:DFFF | $23E | $47:C000 - $47:DFFF | $33E | $67:C000 - $67:DFFF | ||
| $13F | $27:E000 - $27:FFFF | $23F | $47:E000 - $47:FFFF | $33F | $67:E000 - $67:FFFF | ||
