C64-dev/reference/memory-map-complete.md

Commodore 64 — Complete Memory Map Reference

Source: Compute's Mapping the Commodore 64; The Anatomy of the Commodore 64

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Quick-Reference Regions

Range	Size	Description
$0000–$00FF	256 B	Zero Page (fastest addressing)
$0100–$01FF	256 B	CPU Stack
$0200–$03FF	512 B	OS/BASIC work area (vectors, tables)
$0400–$07FF	1 KB	Default screen text matrix (40×25)
$0800–$9FFF	38 KB	BASIC program area (default)
$A000–$BFFF	8 KB	BASIC ROM (or cartridge/RAM under)
$C000–$CFFF	4 KB	Upper RAM (ML friendly)
$D000–$DFFF	4 KB	I/O space (VIC-II/SID/CIA/Color RAM)
$E000–$FFFF	8 KB	Kernal ROM (or RAM under)

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Zero Page — $0000–$00FF (Selected)

Address	Label	Description
$00	R6510	6510 I/O direction register
$01	R6510+1	6510 I/O port (RAM/ROM banking + cassette)
$02	UNUSED	Free zero-page byte
$03–$04	ADRAY1	Convert float→integer vector
$05–$06	ADRAY2	Convert integer→float vector
$07	CHARAC	Search character for BASIC scanner
$08	ENDCHR	Flag: scan to end of BASIC line
$09	TRMPOS	Terminal position for tab
$0A	VERCKK	LOAD (0) or VERIFY (1) flag
$0B	COUNT	Input buffer character count
$0C	DIMFLG	Default (0) or DIM flag
$0D	VALTYP	Type flag: 0=float, $FF=string
$0E	INTFLG	Integer flag
$0F	GARBFL	DATA scan / LIST quote / garbage collect flag
$10	SUBFLG	Subscript flag for FN
$11	INPFLG	INPUT (0) or GET ($40) or READ ($98)
$12	TANSGN	TAN sign / comparison flag
$13	CHANNL	Current I/O channel (0=keyboard/screen)
$14–$15	LINNUM	Integer line number
$16	TEMPPT	Pointer: next temp string
$17–$18	LASTPT	Pointer: last temp string
$19–$21	TEMPST	Temp string descriptor stack
$22–$25	INDEX1	Utility pointer area
$26–$2A	FACEXP	Floating-point accumulator #1
$2B–$2C	TXTTAB	Pointer: start of BASIC text ($0801 default)
$2D–$2E	VARTAB	Pointer: start of BASIC variables
$2F–$30	ARYTAB	Pointer: start of BASIC arrays
$31–$32	STREND	Pointer: end of arrays (+1)
$33–$34	FRETOP	Pointer: bottom of string storage
$35–$36	FRESPC	Utility pointer for strings
$37–$38	MEMSIZ	Pointer: top of memory ($A000 default)
$39–$3A	CURLIN	Current BASIC line number
$3B–$3C	OLDLIN	Previous BASIC line number
$3D–$3E	OLDTXT	Pointer: previous BASIC statement
$3F–$40	DATLIN	Line number of current DATA statement
$41–$42	DATPTR	Pointer into current DATA statement
$43–$44	INPPTR	Pointer: INPUT source
$45–$46	VARNAM	Current variable name
$47–$48	VARPNT	Pointer: current variable value
$49–$4A	FORPNT	Pointer: FOR/NEXT variable
$4B–$4E	OPPTR	Math operator work area
$52–$55	FAC2	Floating-point accumulator #2
$56	ARGSGN	Sign comparison, FAC1 vs FAC2
$57–$58	ARISGN	Sign of result
$59	FACOV	FAC1 overflow byte
$5A–$5B	FBUFPT	Pointer: BASIC print buffer
$61–$66	FAC	FAC1 (5 bytes)
$69–$6E	ARG	FAC2 (5 bytes)
$90	STATUS	Kernal I/O status (ST) word
$91	STKEY	STOP key flag ($7F = pressed)
$93	VERCK	LOAD/VERIFY flag (Kernal)
$94	C3PO	Cassette: 1=write leader sent
$95	BSOUR	Cassette: byte to write
$9A	SXREG	Serial bus I/O address
$9B	RDFNM	Record/file number
$9C	RDEVNM	Record device
$9D	RDSEC	Record secondary address
$9E	RIRQSC	RS-232 recv IRQ state
$9F	STATUS2	RS-232 status
$A0–$A2	TIME	60Hz jiffy clock (24-bit, MSB=$A0)
$A3–$A4	PCTR	Cassette sync / block count
$B0–$B5	EAL	Kernal: device address / sector pointers
$BA	DFLTN	Default input device (0=keyboard)
$BB	DFLTO	Default output device (3=screen)
$BC	PRTY	Cassette parity byte
$BD	DPSW	Cassette EOT flag
$BE	MYCH	Tape character in assembly
$BF	CAS1	Cassette read error correction
$C0	FSBLK	Cassette read: first block flag
$C1–$C2	MXPNT	Pointer: maximum BASIC variable
$C3–$C4	SXPTR	Pointer to tape buffer or screen for cassette
$C5	LSTX	Matrix code of last key pressed
$C6	NDX	Keyboard buffer index (# chars)
$C7	RVS	Reverse mode flag (1=on)
$C8	INDX	Pointer: end of logical input line
$C9–$CA	LXSP	Cursor column and row at I/O start
$CB	SFDX	Flag: shift/commodore key
$CC	BLNSW	Cursor blink enable (0=on)
$CD	BLNCT	Countdown to cursor blink
$CE	GDBLN	Character under cursor (saved)
$CF	BLNON	Last blink state (0=off)
$D0	CRSW	INPUT/GET mode (0=INPUT)
$D1–$D2	PNT	Pointer: current screen line address
$D3	PNTR	Cursor column on current line
$D4	QTSW	Quoted mode flag
$D5	LNMX	Logical line length (39 or 79)
$D6	TBLX	Current cursor row
$D7	DATA	Last character output to screen
$D8	INSRT	Insert mode count
$D9–$F2	LDTB1	Screen line link table (25 entries)
$F3–$F4	USER	Pointer: base of color RAM ($D800)
$F5–$F6	KEYD	Pointer: keyboard decode table
$F7–$F8	RIBUF	RS-232 input buffer pointer
$F9–$FA	ROBUF	RS-232 output buffer pointer
$FB–$FE	FREKZP	Free zero-page bytes (user/ML)
$FF	BASZPT	BASIC: temp for float-to-string

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Page 1 — CPU Stack ($0100–$01FF)

The 6510 stack grows downward from $01FF. SP register holds low byte of current top. Do not use this region for data storage in time-critical IRQs — pushes/pulls compete with JSR/RTS.

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Page 2 — OS Work Area ($0200–$02FF, Selected)

Address	Label	Description
$0200–$0258	BUF	BASIC/Kernal input buffer (89 bytes)
$0259–$0262	LAT	Logical file number table (10 entries)
$0263–$026C	FAT	Device number table (10 entries)
$026D–$0276	SAT	Secondary address table (10 entries)
$0277–$0280	KEYD	Keyboard buffer (10 bytes)
$0281–$0282	MEMSTR	Start of memory pointer ($0800 default)
$0283–$0284	MEMSIZ	Top of memory ($A000 default)
$0285	TIMOUT	Serial IEEE timeout flag
$0286	COLOR	Current foreground color code
$0287	BG COL	Color under cursor
$0288	HIBASE	Screen RAM page ($04 = $0400)
$0289	XMAX	Keyboard buffer max size (10 default)
$028A	RPTFLG	Key repeat flag ($40=repeat all)
$028B	KOUNT	Repeat delay counter
$028C	DELAY	Repeat speed counter
$028D	SHFLAG	Keyboard shift flags
$028E	LSTSHF	Previous shift state
$028F–$0290	KEYLOG	Pointer: keyboard decode logic
$0291	MODE	Shift+Commodore mode (0=switch, 128=lock)
$0292	AUTODN	Screen scroll enable (0=on)
$0293–$0294	M51CTR	RS-232 control register (fake 6551)
$0295–$0296	M51CDR	RS-232 command register
$0297–$0298	M51AJB	RS-232 baud rate (non-standard)
$0299–$029A	RIDBE	RS-232 buffer pointers
$029B–$02FF		Other RS-232/cassette work areas

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Page 3 — Vectors ($0300–$03FF)

Address	Default Points To	Description
$0300–$0301	$E38B	IERROR — BASIC error message vector
$0302–$0303	$A483	IMAIN — BASIC main loop vector
$0304–$0305	$A57C	ICRNCH — Tokenize input line vector
$0306–$0307	$A71A	IQPLOP — List a token vector
$0308–$0309	$A7E4	IGONE — Execute a statement vector
$030A–$030B	$AE86	IEVAL — Evaluate expression vector
$030C	$0	SAREG — .A saved on IRQ
$030D	$00	SXREG — .X saved on IRQ
$030E	$00	SYREG — .Y saved on IRQ
$030F	$00	SPREG — SP saved on IRQ
$0310–$0311	$FE43/$8B	USRPOK — USR() vector (JMP + addr)
$0312–$0313	$EA31	IRQ vector (vectored from $FFFE)
$0314–$0315	$EA31	Hardware IRQ vector (CINV)
$0316–$0317	$FE66	BRK handler vector (CBINV)
$0318–$0319	$FE47	NMI vector (NMINV)
$031A–$031B	$F34A	IOPEN — OPEN routine vector
$031C–$031D	$F291	ICLOSE — CLOSE routine vector
$031E–$031F	$F20E	ICHKIN — CHKIN routine vector
$0320–$0321	$F250	ICKOUT — CKOUT routine vector
$0322–$0323	$F333	ICLRCH — CLRCH routine vector
$0324–$0325	$F157	IBASIN — BASIN/CHRIN routine vector
$0326–$0327	$F1CA	IBSOUT — BSOUT/CHROUT routine vector
$0328–$0329	$F6ED	ISTOP — STOP key check vector
$032A–$032B	$F13E	IGETIN — GETIN routine vector
$032C–$032D	$F32F	ICLALL — CLALL routine vector
$032E–$032F	$FE66	IUSRTO — User-defined load vector
$0330–$0331	$F549	ILOAD — LOAD routine vector
$0332–$0333	$F685	ISAVE — SAVE routine vector

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Screen & Color RAM ($0400–$07FF / $D800–$DBFF)

Region	Address	Notes
Screen Matrix	$0400–$07E7	1000 bytes: 40 cols × 25 rows (default)
Unused	$07E8–$07FF	24 bytes free
Color RAM	$D800–$DBE7	1000 bytes, nibble per cell (low 4 bits)
Color unused	$DBE8–$DBFF	24 bytes

Screen address formula: addr = $0400 + (row × 40) + col

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BASIC Work Area ($0800–$9FFF)

• $0800–$0801 — BASIC start: 2-byte link ($00 $08 if empty)
• $0801–$9FFF — 38,911 bytes available to BASIC programs
• BASIC ROM at $A000 interprets tokenized lines starting at $0801
• POKE 43,1 : POKE 44,8 resets BASIC start pointer

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Upper RAM ($C000–$CFFF)

4 KB of RAM, never overlaid by ROM. Ideal location for:

• ML subroutines called from BASIC
• Custom IRQ handlers
• Character set data

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I/O Space ($D000–$DFFF)

Range	Chip	Function
$D000–$D3FF	VIC-II	Video Interface Controller
$D400–$D7FF	SID	Sound Interface Device
$D800–$DBFF	Color	Color RAM (nibbles)
$DC00–$DCFF	CIA #1	Keyboard, joysticks, IRQ timer
$DD00–$DDFF	CIA #2	Serial bus, VIC bank, NMI timer
$DE00–$DEFF	I/O #1	Cartridge expansion port I/O area 1
$DF00–$DFFF	I/O #2	Cartridge expansion port I/O area 2

When HIRAM=0 or banking overrides I/O region, character ROM or RAM appears instead.

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Banking Control — $0001 (6510 I/O Port)

Bit	Name	0 = …	1 = …
0	LORAM	BASIC ROM disabled	BASIC ROM at $A000 enabled
1	HIRAM	Kernal ROM disabled	Kernal ROM at $E000 enabled
2	CHAREN	Char ROM at $D000	I/O at $D000 enabled
3	CASS WR	Cassette write low	Cassette write high
4	CASS SW	(read only)	Cassette sense line
5	CASS MT	Cassette motor on	Cassette motor off

Common values:

• $37 (binary 00110111) — default: BASIC+Kernal+I/O visible
• $36 — Kernal+I/O visible, BASIC RAM underneath
• $35 — I/O visible, both ROMs as RAM
• $34 — all RAM, no I/O (character ROM at $D000)
• $33 — Kernal ROM, character ROM at $D000, no I/O

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Kernal ROM ($E000–$FFFF, Selected Routines)

Address	Label	Function
$E003	—	Kernal version/signature bytes
$EA31	IRQRTL	Standard IRQ handler entry
$E544	PLOT	Read/set cursor position
$E566	IOBASE	Return CIA base address in .XY
$FF81	SCINIT	Initialize VIC/screen editor
$FF84	IOINIT	Initialize CIA chips
$FF87	RAMTAS	RAM test and zero page init
$FF8A	RESTOR	Restore default vectors
$FF8D	VECTOR	Read/set system vectors
$FF90	SETMSG	Set Kernal message flag
$FF93	SECOND	Send secondary address after LISTEN
$FF96	TKSA	Send secondary address after TALK
$FF99	MEMTOP	Read/set top of memory
$FF9C	MEMBOT	Read/set bottom of memory
$FF9F	SCNKEY	Scan keyboard
$FFA2	SETTMO	Set serial bus timeout
$FFA5	ACPTR	Receive byte from serial bus
$FFA8	CIOUT	Send byte to serial bus
$FFAB	UNTLK	Command device to UNTALK
$FFAE	UNLSN	Command device to UNLISTEN
$FFB1	LISTEN	Command device to LISTEN
$FFB4	TALK	Command device to TALK
$FFB7	READST	Read I/O status word
$FFBA	SETLFS	Set logical/device/secondary address
$FFBD	SETNAM	Set filename address and length
$FFC0	OPEN	Open logical file
$FFC3	CLOSE	Close logical file
$FFC6	CHKIN	Set input channel
$FFC9	CKOUT	Set output channel
$FFCC	CLRCH	Restore default I/O channels
$FFCF	CHRIN	Input character from current channel
$FFD2	CHROUT	Output character to current channel
$FFD5	LOAD	Load file from device
$FFD8	SAVE	Save file to device
$FFDB	SETTIM	Set jiffy clock
$FFDE	RDTIM	Read jiffy clock
$FFE1	STOP	Check STOP key
$FFE4	GETIN	Get character from keyboard buffer
$FFE7	CLALL	Close all channels and files
$FFEA	UDTIM	Increment jiffy clock
$FFED	SCREEN	Return screen dimensions
$FFF0	PLOT	Read/set cursor X/Y position
$FFF3	IOBASE	Return I/O base address
$FFFA	—	NMI vector (points into Kernal)
$FFFC	—	RESET vector ($FCE2)
$FFFE	—	IRQ/BRK vector ($FF48)

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VIC-II Bank Selection (via CIA #2, $DD00)

Bits 0–1	VIC Bank	Address Range
11	0	$0000–$3FFF
10	1	$4000–$7FFF
01	2	$8000–$BFFF
00	3	$C000–$FFFF

Default: Bank 0 ($0000–$3FFF) — screen at $0400, charset at $1000 (ROM image).

Character ROM is mirrored into VIC banks 0 and 2 at offsets $1000 and $1800.

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Sprite Memory Layout

Each sprite = 64 bytes (63 data + 1 padding). Pointer bytes stored at screen RAM + $03F8 (8 bytes).

Pointer Value	Sprite Data Address (Bank 0)
$0D	$0340
$0E	$0380
$0F	$03C0
$80	$2000
$81	$2040
…	…

sprite_addr = bank_base + (pointer_value × 64)