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14KB
14KB
name: memory-map description: > Use this skill for questions about C64 memory organization, zero page locations, memory banking, PEEK/POKE addresses, sprite memory, screen RAM, color RAM, protecting ML programs, and placing data/code in RAM. Sources: COMPUTE!‘s Mapping the Commodore 64, The Anatomy of the C64, The Complete C64 ROM Disassembly.
Commodore 64 Memory Map
Complete Address Space
Address Decimal Contents (default banking)
----------- ------------- ----------------------------------------
$0000 0 6510 I/O direction register
$0001 1 6510 I/O port (bank control/tape/motor)
$0002 2 Unused (3 free bytes: $02)
$0003-$0004 3-4 Float→integer vector (ADRAY1)
$0005-$0006 5-6 Integer→float vector (ADRAY2)
$0007 7 Search character (BASIC)
$0008 8 Quote mode flag
$0009 9 TAB column counter
$000A 10 Load/Verify flag (0=LOAD, 1=VERIFY)
$000B 11 Input buffer pointer / subscript counter
$000C 12 Default DIM flag
$000E 14 Type flag (80=integer, 00=float)
$000F 15 DATA scan / LIST quote / memory flag
$0010 16 Subscript / FNx flag
$0011 17 0=INPUT, $40=GET, $98=READ
$0012 18 ATN sign / comparison flag
$0013 19 Current I/O prompt flag
$0014-$0015 20-21 Integer value temporary
$0016 22 Pointer to temp string stack
$0017-$0018 23-24 Last temp string vector
$0019-$0021 25-33 Stack for temporary strings
$0022-$0025 34-37 Miscellaneous work area
$0026-$002A 38-42 Product area (math)
$002B-$002C 43-44 TXTTAB — pointer to start of BASIC text
$002D-$002E 45-46 VARTAB — start of variable storage
$002F-$0030 47-48 ARYTAB — start of array storage
$0031-$0032 49-50 STREND — end of array storage (+1)
$0033-$0034 51-52 FRETOP — top of free string space
$0035-$0036 53-54 FRESPC — string utility pointer
$0037-$0038 55-56 MEMSIZ — pointer to end of memory / bottom of strings
$0039-$003A 57-58 CURLIN — current BASIC line number
$003B-$003C 59-60 OLDLIN — previous BASIC line number
$003D-$003E 61-62 OLDTXT — pointer to previous BASIC statement
$003F-$0040 63-64 DATLIN — line number of current DATA statement
$0041-$0042 65-66 DATPTR — pointer to current DATA item
$0043-$0044 67-68 INPPTR — INPUT source pointer
$0045-$0046 69-70 VARNAM — name of current variable
$0047-$0048 71-72 VARPNT — pointer to current variable
$0049-$004A 73-74 FORPNT — pointer to FOR/NEXT variable
$004B 75 OPPTR — operator precedence
$004C 76 OPMASK — mask for operator
$004D-$0050 77-80 TEMPPT — temp string and area
$0051 81 LASTPT — pointer to last temp string
$0052-$0053 82-83 TEMPST — pointer to string
$0054 84 INDEX (low), INDEX+1 (high)
$005E 94 FAC#2 (floating point accumulator #2)
$0060-$0066 96-102 FAC#1 (floating point accumulator #1, 5 bytes + sign/exp)
$006F 111 Pointer to start of string being processed
$0071-$0072 113-114 RESULT — pointer to end of string
$0073 115 Jump instruction for USR
$0074-$0075 116-117 USR function address (JSR target)
$0076 118 CHARAC — search character
$007A-$007B 122-123 FNPNT — pointer for FN functions
$00AC-$00AD 172-173 STRNG1 — string 1 pointer
$00AE-$00AF 174-175 STRNG2 — string 2 pointer
$00B7 183 FNLEN — length of filename
$00B8 184 LOGICAL — logical file number
$00B9 185 DFLTO — output device number
$00BA 186 DFLTI — input device number
$00BB 187 SA — secondary address
$00BC 188 EAL — tape end address (low)
$00BD 189 EAH — tape end address (high)
$00BE 190 TAPE1 — tape buffer pointer
$00BF 191 COUNT — tape character counter
$00C0 192 INIT — tape signal level
$00C1 193 SKPO — skip byte count
$00C2 194 BPTR — tape data pointer
$00C3-$00C4 195-196 TAPE2 — tape end buffer pointer
$00C5 197 LSTX — last key pressed (keyboard matrix row)
$00C6 198 NDX — number of characters in keyboard buffer
$00C7 199 RVS — reverse mode flag (1=reverse on)
$00C8 200 INDX — end-of-line pointer for current screen line
$00C9-$00CA 201-202 LNMX — pointer to cursor on screen
$00CB 203 SCHAR — character under cursor
$00CC 204 BLNSW — cursor blink switch (0=blink)
$00CD 205 BLNCT — countdown to cursor blink
$00CE 206 GDBLN — char under cursor (save)
$00CF 207 BLNON — cursor blink status (0=off)
$00D0 208 CRSW — flag: 0=cursor in key queue, 1=not
$00D1-$00D2 209-210 PNT — pointer to cursor line in screen RAM
$00D3 211 PNTR — column of cursor on screen
$00D4 212 QTSW — quote mode flag
$00D5 213 LNMX — screen line length (39 or 79)
$00D6 214 TBLX — current cursor row (0-24)
$00D7 215 Spare byte
$00D8 216 INSRT — insert mode count
$00D9-$00F2 217-242 LDTB1 — line link table (25 lines)
$00F3-$00F4 243-244 USER — pointer to color RAM for cursor line
$00F5-$00F6 245-246 KEYTAB — pointer to keyboard decode table
$00F7-$00F8 247-248 RIBUF — RS-232 input buffer pointer
$00F9-$00FA 249-250 ROBUF — RS-232 output buffer pointer
$00FB-$00FE 251-254 FREKZP — FREE ZERO PAGE (user programs)
$00FF 255 (used by BASIC math)
$0100-$01FF 256-511 6510 Stack (grows down from $01FF)
$0200-$0258 512-600 Basic input buffer (80 chars)
$0259-$0262 601-610 LDTB2 — open file logical-number table
$0263-$026C 611-620 LATBL — open file device-number table
$026D-$0276 621-630 SATBL — open file secondary-address table
$0277-$0280 631-640 Keyboard buffer (10 chars, FIFO)
$0281-$0282 641-642 MEMBOT — bottom of memory pointer
$0283-$0284 643-644 MEMTOP — top of memory pointer
$0285 645 TIMOUT — serial bus timeout flag
$0286 646 COLOR — current text foreground color
$0287 647 BDRCLR — border color at cursor
$0288 648 HIBASE — high byte of screen RAM base ($04 = $0400)
$0289 649 XMAX — max chars in keyboard buffer (default: 10)
$028A 650 RPTFLG — key repeat flag (0=cursor keys+INS/DEL only)
$028B 651 KOUNT — repeat delay counter
$028C 652 DELAY — repeat speed counter
$028D 653 SHFLAG — shift/ctrl/C= key flags
$028E 654 LSTSHF — previous shift key state
$028F-$0290 655-656 KEYLOG — pointer to keyboard decode logic
$0291 657 DFLTN — default input device (0=keyboard)
$0292 658 DFLTO — default output device (3=screen)
$0293 659 PRTY — serial bus parity
$0294 660 DPSW — serial bus deferred character flag
$0295 661 MSGFLG — OS message flag
$0296 662 ARGT — type of FAC#1 argument
$0297 663 ERRNUM — BASIC error number
$0298 664 ERRSAV — BASIC error line save
$0299-$029A 665-666 IOLINK — I/O start address
$029B-$029E 667-670 TRPTAB — trap vectors
$02A1-$02FF 673-767 Free RAM (87 bytes)
$0300-$0301 768-769 IERROR — indirect BASIC error vector
$0302-$0303 770-771 IMAIN — indirect BASIC main loop vector
$0304-$0305 772-773 ICRNCH — indirect BASIC crunch vector
$0306-$0307 774-775 IQPLOP — indirect BASIC LIST vector
$0308-$0309 776-777 IGONE — indirect BASIC execute vector
$030A-$030B 778-779 IEVAL — indirect BASIC expression evaluate vector
$030C 780 SAREG — A register save on SYS
$030D 781 SXREG — X register save on SYS
$030E 782 SYREG — Y register save on SYS
$030F 783 SPREG — Status register save on SYS
$0310-$0311 784-785 USRPOK — USR function vector (JMP opcode + address)
$0312-$0313 786-787 (USR vector high byte + unused)
$0314-$0315 788-789 CINV — IRQ vector (default: $EA31)
$0316-$0317 790-791 CBINV — BRK vector (default: $FE66)
$0318-$0319 792-793 NMINV — NMI vector (default: $FE47)
$031A-$031B 794-795 IOPEN — indirect OPEN vector
$031C-$031D 796-797 ICLOSE — indirect CLOSE vector
$031E-$031F 798-799 ICHKIN — indirect CHKIN vector
$0320-$0321 800-801 ICHKOUT — indirect CHKOUT vector
$0322-$0323 802-803 ICLRCH — indirect CLRCH vector
$0324-$0325 804-805 IBASIN — indirect BASIN (CHRIN) vector
$0326-$0327 806-807 IBSOUT — indirect BSOUT (CHROUT) vector
$0328-$0329 808-809 ISTOP — indirect STOP vector
$032A-$032B 810-811 IGETIN — indirect GETIN vector
$032C-$032D 812-813 ICLALL — indirect CLALL vector
$032E-$032F 814-815 USRCMD — user-defined command vector
$0330-$0331 816-817 ILOAD — indirect LOAD vector
$0332-$0333 818-819 ISAVE — indirect SAVE vector
$0334-$033B 820-827 (spare)
$033C-$03FB 828-1019 Cassette buffer (192 bytes)
$03FC-$03FF 1020-1023 (free)
$0400-$07E7 1024-2023 Screen RAM (default: 40×25 = 1000 bytes)
$07E8-$07FF 2024-2047 Sprite pointers (8 bytes, one per sprite)
$0800-$9FFF 2048-40959 BASIC program area (38912 bytes)
$A000-$BFFF 40960-49151 BASIC ROM (or RAM when banked out)
$C000-$CFFF 49152-53247 Upper RAM (always RAM, 4KB)
$D000-$D3FF 53248-54271 VIC-II chip registers (I/O mode)
$D000-$DFFF 53248-57343 Character ROM (when CHAREN=0)
$D400-$D7FF 54272-55295 SID chip registers
$D800-$DBFF 55296-56319 Color RAM (nybbles, 1000 bytes)
$DC00-$DCFF 56320-56575 CIA #1 (keyboard, joystick, IRQ timer)
$DD00-$DDFF 56576-56831 CIA #2 (serial bus, NMI, VIC bank)
$DE00-$DEFF 56832-57087 I/O area 1 (expansion port)
$DF00-$DFFF 57088-57343 I/O area 2 (expansion port)
$E000-$FFFF 57344-65535 Kernal ROM (or RAM when banked out)
Memory Banking
The C64 uses soft banking via location $0001 (6510 I/O port).
| $0001 Bits 2-0 | LORAM | HIRAM | CHAREN | Memory Configuration |
|---|---|---|---|---|
| %111 (7) | BASIC ROM | Kernal ROM | I/O | Normal (default) |
| %110 (6) | RAM | Kernal ROM | I/O | ML programs using Kernal |
| %101 (5) | BASIC ROM | Kernal ROM | Char ROM | Character ROM visible |
| %100 (4) | RAM | RAM | I/O | All RAM + I/O |
| %011 (3) | RAM | RAM | Char ROM | All RAM + Char ROM |
| %010 (2) | RAM | RAM | Char ROM | All RAM + Char ROM |
| %001 (1) | RAM | RAM | RAM | All 64KB RAM |
| %000 (0) | RAM | RAM | RAM | All 64KB RAM |
Direction register at $0000 should have bits 0, 1, 2, 3, 5 as outputs: POKE 0, 47 (default).
; Bank out BASIC, keep Kernal + I/O (common for ML programs)
LDA $0001
AND #$FE ; clear bit 0 (LORAM)
STA $0001
; Restore normal
LDA $0001
ORA #$07 ; set bits 0-2
STA $0001
VIC-II Memory Banking
The VIC-II chip sees a 16KB bank of memory selected by CIA #2 Port A bits 0-1:
| $DD00 bits 1-0 | VIC-II Bank | Address Range |
|---|---|---|
| %11 (3) | Bank 0 | $0000–$3FFF (default) |
| %10 (2) | Bank 1 | $4000–$7FFF |
| %01 (1) | Bank 2 | $8000–$BFFF |
| %00 (0) | Bank 3 | $C000–$FFFF |
Note: Banks 0 and 2 have Character ROM “mirrored” at offsets $1000–$1FFF and $9000–$9FFF. This means the VIC-II sees character data even though the CPU cannot (in normal banking).
' Switch VIC to Bank 1 ($4000-$7FFF)
POKE 56576, (PEEK(56576) AND 252) OR 2
Sprite Memory
Each sprite needs 64 bytes of data. Sprite data must be within the VIC-II's currently active 16KB bank.
- Sprite pointer table: Located at top of current screen RAM + offsets $F8–$FF
- Default: $07F8–$07FF (when screen is at $0400)
- Pointer value = sprite data address / 64 (within the VIC-II bank)
- Default safe areas for sprite data: Blocks 11–14 at $02C0–$03BF (within default Bank 0)
' Place sprite 0 data at block 13 ($0340)
POKE 2040, 13 ' sprite 0 pointer ($07F8) = block 13
' Now fill $0340-$037F with sprite pixel data
Protecting ML Code from BASIC
Method 1 — Lower BASIC top:
POKE 56, 192 : CLR ' MEMSIZ high byte = $C0, BASIC top = $C000
' Now place ML at $C000 safely
Method 2 — Raise BASIC bottom:
POKE 44, 18 : POKE 4608, 0 : CLR ' Start BASIC at $1200
' Place ML at $0800–$11FF
Method 3 — Use cassette buffer at $033C–$03FB (192 bytes):
' Safe for short routines; no special protection needed
FOR I = 828 TO 828+N : READ D : POKE I,D : NEXT
SYS 828
Key POKE/PEEK Locations for BASIC Programmers
| POKE/PEEK | Address | Effect |
|---|---|---|
POKE 53280, N |
$D020 | Border color (0-15) |
POKE 53281, N |
$D021 | Background color 0 (0-15) |
POKE 646, N |
$0286 | Text foreground color (0-15) |
POKE 53265, PEEK(53265) OR 32 |
$D011 bit 5 | Switch to bitmap mode |
POKE 53272, N |
$D018 | VIC-II memory control |
POKE 648, N |
$0288 | Screen RAM high byte (4=$0400, 8=$0800 etc) |
PEEK(197) |
$00C5 | Last key scan code (no key = 64) |
PEEK(198) |
$00C6 | Number of chars in keyboard buffer |
PEEK(653) |
$028D | Shift/Ctrl/C= key status |
POKE 650, 128 |
$028A | Enable key repeat for all keys |
POKE 56334, PEEK(56334) AND 254 |
$DC0E | Disable timer (stop CIA #1 timer A) |
POKE 788, 52 : POKE 789, 193 |
$0314/15 | IRQ vector → $C134 (example) |