Commodore 64 memory map

Address
(hex, dec)
Description
$0000-$00FF, 0-256
Zero page
$0000
0

Processor port data direction register. Bits:

  • Bit #x: 0 = Bit #x in processor port can only be read; 1 = Bit #x in processor port can be read and written.

Default: $2F, %00101111.

$0001
1

Processor port. Bits:

  • Bits #0-#2: Configuration for memory areas $A000-$BFFF, $D000-$DFFF and $E000-$FFFF. Values:

    • %x00: RAM visible in all three areas.

    • %x01: RAM visible at $A000-$BFFF and $E000-$FFFF.

    • %x10: RAM visible at $A000-$BFFF; KERNAL ROM visible at $E000-$FFFF.

    • %x11: BASIC ROM visible at $A000-$BFFF; KERNAL ROM visible at $E000-$FFFF.

    • %0xx: Character ROM visible at $D000-$DFFF. (Except for the value %000, see above.)

    • %1xx: I/O area visible at $D000-$DFFF. (Except for the value %100, see above.)

  • Bit #3: Datasette output signal level.

  • Bit #4: Datasette button status; 0 = One or more of PLAY, RECORD, F.FWD or REW pressed; 1 = No button is pressed.

  • Bit #5: Datasette motor control; 0 = On; 1 = Off.

Default: $37, %00110111.

$0002
2

Unused.

$0003-$0004
3-4

Unused.
Default: $B1AA, execution address of routine converting floating point to integer.

$0005-$0006
5-6

Unused.
Default: $B391, execution address of routine converting integer to floating point.

$0007
7

Byte being search for during various operations.
Current digit of number being input.
Low byte of first integer operand during AND and OR.
Low byte of integer-format FAC during INT().

$0008
8

Byte being search for during various operations.
Current byte of BASIC line during tokenization.
High byte of first integer operand during AND and OR.

$0009
9

Current column number during SPC() and TAB().

$000A
10

LOAD/VERIFY switch. Values:

  • $00: LOAD.

  • $01-$FF: VERIFY.

$000B
11

Current token during tokenization.
Length of BASIC line during insertion of line.
AND/OR switch; $00 = AND; $FF = OR.
Number of dimensions during array operations.

$000C
12

Switch for array operations. Values:

  • $00: Operation was not called by DIM.

  • $40-$7F: Operation was called by DIM.

$000D
13

Current expression type. Values:

  • $00: Numerical.

  • $FF: String.

$000E
14

Current numerical expression type. Bits:

  • Bit #7: 0 = Floating point; 1 = Integer.

$000F
15

Quotation mode switch during tokenization; Bit #6: 0 = Normal mode; 1 = Quotation mode.
Quotation mode switch during LIST; $01 = Normal mode; $FE = Quotation mode.
Garbage collection indicator during memory allocation for string variable; $00-$7F = There was no garbage collection yet; $80 = Garbage collection already took place.

$0010
16

Switch during fetch of variable name. Values:

  • $00: Integer variables are accepted.

  • $01-$FF: Integer variables are not accepted.

$0011
17

GET/INPUT/READ switch. Values:

  • $00: INPUT.

  • $40: GET.

  • $98: READ.

$0012
18

Sign during SIN() and TAN(). Values:

  • $00: Positive.

  • $FF: Negative.

$0013
19

Current I/O device number.
Default: $00, keyboard for input and screen for output.

$0014-$0015
20-21

Line number during GOSUB, GOTO and RUN.
Second line number during LIST.
Memory address during PEEK, POKE, SYS and WAIT.

$0016
22

Pointer to next expression in string stack. Values: $19; $1C; $1F; $22.
Default: $19.

$0017-$0018
23-24

Pointer to previous expression in string stack.

$0019-$0021
25-33

String stack, temporary area for processing string expressions (9 bytes, 3 entries).

$0022-$0025
34-37

Temporary area for various operations (4 bytes).

$0026-$0029
38-41

Auxiliary arithmetical register for division and multiplication (4 bytes).

$002A
42

Unused.

$002B-$002C
43-44

Pointer to beginning of BASIC area.
Default: $0801, 2049.

$002D-$002E
45-46

Pointer to beginning of variable area. (End of program plus 1.)

$002F-$0030
47-48

Pointer to beginning of array variable area.

$0031-$0032
49-50

Pointer to end of array variable area.

$0033-$0034
51-52

Pointer to beginning of string variable area. (Grows downwards from end of BASIC area.)

$0035-$0036
53-54

Pointer to memory allocated for current string variable.

$0037-$0038
55-56

Pointer to end of BASIC area.
Default: $A000, 40960.

$0039-$003A
57-58

Current BASIC line number. Values:

  • $0000-$F9FF, 0-63999: Line number.

  • $FF00-$FFFF: Direct mode, no BASIC program is being executed.

$003B-$003C
59-60

Current BASIC line number for CONT.

$003D-$003E
61-62

Pointer to next BASIC instruction for CONT. Values:

  • $0000-$00FF: CONT'ing is not possible.

  • $0100-$FFFF: Pointer to next BASIC instruction.

$003F-$0040
63-64

BASIC line number of current DATA item for READ.

$0041-$0042
65-66

Pointer to next DATA item for READ.

$0043-$0044
67-68

Pointer to input result during GET, INPUT and READ.

$0045-$0046
69-70

Name and type of current variable. Bits:

  • $0045 bits #0-#6: First character of variable name.

  • $0046 bits #0-#6: Second character of variable name; $00 = Variable name consists of only one character.

  • $0045 bit #7 and $0046 bit #7:

    • %00: Floating-point variable.

    • %01: String variable.

    • %10: FN function, created with DEF FN.

    • %11: Integer variable.

$0047-$0048
71-72

Pointer to value of current variable or FN function.

$0049-$004A
73-74

Pointer to value of current variable during LET.
Value of second and third parameter during WAIT.
Logical number and device number during OPEN.
$0049, 73: Logical number of CLOSE.
Device number of LOAD, SAVE and VERIFY.

$004B-$004C
75-76

Temporary area for saving original pointer to current BASIC instruction during GET, INPUT and READ.

$004D
77

Comparison operator indicator. Bits:

  • Bit #1: 1 = ">" (greater than) is present in expression.

  • Bit #2: 1 = "=" (equal to) is present in expression.

  • Bit #3: 1 = "<" (less than) is present in expression.

$004E-$004F
78-79

Pointer to current FN function.

$0050-$0051
80-81

Pointer to current string variable during memory allocation.

$0052
82

Unused.

$0053
83

Step size of garbage collection. Values: $03; $07.

$0054-$0056
84-86

JMP ABS machine instruction, jump to current BASIC function.
$0055-$0056, 85-86: Execution address of current BASIC function.

$0057-$005B
87-91

Arithmetic register #3 (5 bytes).

$005C-$0060
92-96

Arithmetic register #4 (5 bytes).

$0061-$0065
97-101

FAC, arithmetic register #1 (5 bytes).

$0066
102

Sign of FAC. Bits:

  • Bit #7: 0 = Positive; 1 = Negative.

$0067
103

Number of degrees during polynomial evaluation.

$0068
104

Temporary area for various operations.

$0069-$006D
105-109

ARG, arithmetic register #2 (5 bytes).

$006E
110

Sign of ARG. Bits:

  • Bit #7: 0 = Positive; 1 = Negative.

$006F-$0070
111-112

Pointer to first string expression during string comparison.

$0071-$0072
113-114

Auxiliary pointer during array operations.
Temporary area for saving original pointer to current BASIC instruction during VAL().
Pointer to current item of polynomial table during polynomial evaluation.

$0073-$008A
115-138

CHRGET. Machine code routine to read next byte from BASIC program or direct command (24 bytes).
$0079, 121: CHRGOT. Read current byte from BASIC program or direct command.
$007A-$007B, 122-123: Pointer to current byte in BASIC program or direct command.

$008B-$008F
139-143

Previous result of RND().

$0090
144

Value of ST variable, device status for serial bus and datasette input/output. Serial bus bits:

  • Bit #0: Transfer direction during which the timeout occured; 0 = Input; 1 = Output.

  • Bit #1: 1 = Timeout occurred.

  • Bit #4: 1 = VERIFY error occurred (only during VERIFY), the file read from the device did not match that in the memory.

  • Bit #6: 1 = End of file has been reached.

  • Bit #7: 1 = Device is not present.

Datasette bits:

  • Bit #2: 1 = Block is too short (shorter than 192 bytes).

  • Bit #3: 1 = Block is too long (longer than 192 bytes).

  • Bit #4: 1 = Not all bytes read with error during pass 1 could be corrected during pass 2, or a VERIFY error occurred, the file read from the device did not match that in the memory.

  • Bit #5: 1 = Checksum error occurred.

  • Bit #6: 1 = End of file has been reached (only during reading data files).

$0091
145

Stop key indicator. Values:

  • $7F: Stop key is pressed.

  • $FF: Stop key is not pressed.

$0092
146

Unknown. (Timing constant during datasette input.)

$0093
147

LOAD/VERIFY switch. Values:

  • $00: LOAD.

  • $01-$FF: VERIFY.

$0094
148

Serial bus output cache status. Bits:

  • Bit #7: 1 = Output cache dirty, must transfer cache contents upon next output to serial bus.

$0095
149

Serial bus output cache, previous byte to be sent to serial bus.

$0096
150

Unknown. (End of tape indicator during datasette input/output.)

$0097
151

Temporary area for saving original value of Y register during input from RS232.
Temporary area for saving original value of X register during input from datasette.

$0098
152

Number of files currently open. Values: $00-$0A, 0-10.

$0099
153

Current input device number.
Default: $00, keyboard.

$009A
154

Current output device number.
Default: $03, screen.

$009B
155

Unknown. (Parity bit during datasette input/output.)

$009C
156

Unknown. (Byte ready indicator during datasette input/output.)

$009D
157

System error display switch. Bits:

  • Bit #6: 0 = Suppress I/O error messages; 1 = Display them.

  • Bit #7: 0 = Suppress system messages; 1 = Display them.

$009E
158

Byte to be put into output buffer during RS232 and datasette output.
Block header type during datasette input/output.
Length of file name during datasette input/output.
Error counter during LOAD from datasette. Values: $00-$3E, 0-62.

$009F
159

Auxiliary counter for writing file name into datasette buffer.
Auxiliary counter for comparing requested file name with file name read from datasette during datasette input.
Error correction counter during LOAD from datasette. Values: $00-$3E, 0-62.

$00A0-$00A2
160-162

Value of TI variable, time of day, increased by 1 every 1/60 second (on PAL machines). Values: $000000-$4F19FF, 0-518399 (on PAL machines).

$00A3
163

EOI switch during serial bus output. Bits:

  • Bit #7: 0 = Send byte right after handshake; 1 = Do EOI delay first.

Bit counter during datasette output.

$00A4
164

Byte buffer during serial bus input.
Parity during datasette input/output.

$00A5
165

Bit counter during serial bus input/output.
Counter for sync mark during datasette output.

$00A6
166

Offset of current byte in datasette buffer.

$00A7
167

Bit buffer during RS232 input.

$00A8
168

Bit counter during RS232 input.

$00A9
169

Stop bit switch during RS232 input. Values:

  • $00: Data bit.

  • $01-$FF: Stop bit.

$00AA
170

Byte buffer during RS232 input.

$00AB
171

Parity during RS232 input.
Computed block checksum during datasette input.

$00AC-$00AD
172-173

Start address for SAVE to serial bus.
Pointer to current byte during SAVE to serial bus or datasette.
Pointer to line in screen memory to be scrolled during scrolling the screen.

$00AE-$00AF
174-175

Load address read from input file and pointer to current byte during LOAD/VERIFY from serial bus.
End address after LOAD/VERIFY from serial bus or datasette.
End address for SAVE to serial bus or datasette.
Pointer to line in Color RAM to be scrolled during scrolling the screen.

$00B0-$00B1
176-177

Unknown.

$00B2-$00B3
178-179

Pointer to datasette buffer.
Default: $033C, 828.

$00B4
180

Bit counter and stop bit switch during RS232 output. Bits:

  • Bits #0-#6: Bit count.

  • Bit #7: 0 = Data bit; 1 = Stop bit.

Bit counter during datasette input/output.

$00B5
181

Bit buffer (in bit #2) during RS232 output.

$00B6
182

Byte buffer during RS232 output.

$00B7
183

Length of file name or disk command; first parameter of LOAD, SAVE and VERIFY or fourth parameter of OPEN. Values:

  • $00: No parameter.

  • $01-$FF: Parameter length.

$00B8
184

Logical number of current file.

$00B9
185

Secondary address of current file.

$00BA
186

Device number of current file.

$00BB-$00BC
187-188

Pointer to current file name or disk command; first parameter of LOAD, SAVE and VERIFY or fourth parameter of OPEN.

$00BD
189

Parity during RS232 output.
Byte buffer during datasette input/output.

$00BE
190

Block counter during datasette input/output.

$00BF
191

Unknown.

$00C0
192

Datasette motor switch. Values:

  • $00: No button was pressed, motor has been switched off. If a button is pressed on the datasette, must switch motor on.

  • $01-$FF: Motor is on.

$00C1-$00C2
193-194

Start address during SAVE to serial bus, LOAD and VERIFY from datasette and SAVE to datasette.
Pointer to current byte during memory test.

$00C3-$00C4
195-196

Start address for a secondary address of 0 for LOAD and VERIFY from serial bus or datasette.
Pointer to ROM table of default vectors during initialization of I/O vectors.

$00C5
197

Matrix code of key previously pressed. Values:

  • $00-$3F: Keyboard matrix code.

  • $40: No key was pressed at the time of previous check.

$00C6
198

Length of keyboard buffer. Values:

  • $00, 0: Buffer is empty.

  • $01-$0A, 1-10: Buffer length.

$00C7
199

Reverse mode switch. Values:

  • $00: Normal mode.

  • $12: Reverse mode.

$00C8
200

Length of line minus 1 during screen input. Values: $27, 39; $4F, 79.

$00C9
201

Cursor row during screen input. Values: $00-$18, 0-24.

$00CA
202

Cursor column during screen input. Values: $00-$27, 0-39.

$00CB
203

Matrix code of key currently being pressed. Values:

  • $00-$3F: Keyboard matrix code.

  • $40: No key is currently pressed.

$00CC
204

Cursor visibility switch. Values:

  • $00: Cursor is on.

  • $01-$FF: Cursor is off.

$00CD
205

Delay counter for changing cursor phase. Values:

  • $00, 0: Must change cursor phase.

  • $01-$14, 1-20: Delay.

$00CE
206

Screen code of character under cursor.

$00CF
207

Cursor phase switch. Values:

  • $00: Cursor off phase, original character visible.

  • $01: Cursor on phase, reverse character visible.

$00D0
208

End of line switch during screen input. Values:

  • $00: Return character reached, end of line.

  • $01-$FF: Still reading characters from line.

$00D1-$00D2
209-210

Pointer to current line in screen memory.

$00D3
211

Current cursor column. Values: $00-$27, 0-39.

$00D4
212

Quotation mode switch. Values:

  • $00: Normal mode.

  • $01: Quotation mode.

$00D5
213

Length of current screen line minus 1. Values: $27, 39; $4F, 79.

$00D6
214

Current cursor row. Values: $00-$18, 0-24.

$00D7
215

PETSCII code of character during screen input/output.
Bit buffer during datasette input.
Block checksum during datasette output.

$00D8
216

Number of insertions. Values:

  • $00: No insertions made, normal mode, control codes change screen layout or behavior.

  • $01-$FF: Number of insertions, when inputting this many character next, those must be turned into control codes, similarly to quotation mode.

$00D9-$00F1
217-241

High byte of pointers to each line in screen memory (25 bytes). Values:

  • $00-$7F: Pointer high byte.

  • $80-$FF: No pointer, line is an extension of previous line on screen.

$00F2
242

Temporary area during scrolling the screen.

$00F3-$00F4
243-244

Pointer to current line in Color RAM.

$00F5-$00F6
245-246

Pointer to current conversion table during conversion from keyboard matrix codes to PETSCII codes.

$00F7-$00F8
247-248

Pointer to RS232 input buffer. Values:

  • $0000-$00FF: No buffer defined, a new buffer must be allocated upon RS232 input.

  • $0100-$FFFF: Buffer pointer.

$00F9-$00FA
249-250

Pointer to RS232 output buffer. Values:

  • $0000-$00FF: No buffer defined, a new buffer must be allocated upon RS232 output.

  • $0100-$FFFF: Buffer pointer.

$00FB-$00FE
251-254

Unused (4 bytes).

$00FF-$010A
255-266

Buffer for conversion from floating point to string (12 bytes.)

$0100-$01FF, 256-511
Processor stack
$00FF-$010A
255-266

Buffer for conversion from floating point to string (12 bytes.)

$0100-$013D
256-317

Pointers to bytes read with error during datasette input (62 bytes, 31 entries).

$0100-$01FF
256-511

Processor stack. Also used for storing data related to FOR and GOSUB.

$0200-$02FF, 512-767
$0200-$0258
512-600

Input buffer, storage area for data read from screen (89 bytes).

$0259-$0262
601-610

Logical numbers assigned to files (10 bytes, 10 entries).

$0263-$026C
611-620

Device numbers assigned to files (10 bytes, 10 entries).

$026D-$0276
621-630

Secondary addresses assigned to files (10 bytes, 10 entries).

$0277-$0280
631-640

Keyboard buffer (10 bytes, 10 entries).

$0281-$0282
641-642

Pointer to beginning of BASIC area after memory test.
Default: $0800, 2048.

$0283-$0284
643-644

Pointer to end of BASIC area after memory test.
Default: $A000, 40960.

$0285
645

Unused. (Serial bus timeout.)

$0286
646

Current color, cursor color. Values: $00-$0F, 0-15.

$0287
647

Color of character under cursor. Values: $00-$0F, 0-15.

$0288
648

High byte of pointer to screen memory for screen input/output.
Default: $04, $0400, 1024.

$0289
649

Maximum length of keyboard buffer. Values:

  • $00, 0: No buffer.

  • $01-$0F, 1-15: Buffer size.

$028A
650

Keyboard repeat switch. Bits:

  • Bits #6-#7: %00 = Only cursor up/down, cursor left/right, Insert/Delete and Space repeat; %01 = No key repeats; %1x = All keys repeat.

$028B
651

Delay counter during repeat sequence, for delaying between successive repeats. Values:

  • $00, 0: Must repeat key.

  • $01-$04, 1-4: Delay repetition.

$028C
652

Repeat sequence delay counter, for delaying before first repetition. Values:

  • $00, 0: Must start repeat sequence.

  • $01-$10, 1-16: Delay repeat sequence.

$028D
653

Shift key indicator. Bits:

  • Bit #0: 1 = One or more of left Shift, right Shift or Shift Lock is currently being pressed or locked.

  • Bit #1: 1 = Commodore is currently being pressed.

  • Bit #2: 1 = Control is currently being pressed.

$028E
654

Previous value of shift key indicator. Bits:

  • Bit #0: 1 = One or more of left Shift, right Shift or Shift Lock was pressed or locked at the time of previous check.

  • Bit #1: 1 = Commodore was pressed at the time of previous check.

  • Bit #2: 1 = Control was pressed at the time of previous check.

$028F-$0290
655-656

Execution address of routine that, based on the status of shift keys, sets the pointer at memory address $00F5-$00F6 to the appropriate conversion table for converting keyboard matrix codes to PETSCII codes.
Default: $EB48.

$0291
657

Commodore-Shift switch. Bits:

  • Bit #7: 0 = Commodore-Shift is disabled; 1 = Commodore-Shift is enabled, the key combination will toggle between the uppercase/graphics and lowercase/uppercase character set.

$0292
658

Scroll direction switch during scrolling the screen. Values:

  • $00: Insertion of line before current line, current line and all lines below it must be scrolled 1 line downwards.

  • $01-$FF: Bottom of screen reached, complete screen must be scrolled 1 line upwards.

$0293
659

RS232 control register. Bits:

  • Bits #0-#3: Baud rate, transfer speed. Values:

    • %0000: User specified.

    • %0001: 50 bit/s.

    • %0010: 75 bit/s.

    • %0011: 110 bit/s.

    • %0100: 150 bit/s.

    • %0101: 300 bit/s.

    • %0110: 600 bit/s.

    • %0111: 1200 bit/s.

    • %1000: 2400 bit/s.

    • %1001: 1800 bit/s.

    • %1010: 2400 bit/s.

    • %1011: 3600 bit/s.

    • %1100: 4800 bit/s.

    • %1101: 7200 bit/s.

    • %1110: 9600 bit/s.

    • %1111: 19200 bit/s.

  • Bits #5-#6: Byte size, number of data bits per byte; %00 = 8; %01 = 7, %10 = 6; %11 = 5.

  • Bit #7: Number of stop bits; 0 = 1 stop bit; 1 = 2 stop bits.

$0294
660

RS232 command register. Bits:

  • Bit #0: Synchronization type; 0 = 3 lines; 1 = X lines.

  • Bit #4: Transmission type; 0 = Duplex; 1 = Half duplex.

  • Bits #5-#7: Parity mode. Values:

    • %xx0: No parity check, bit #7 does not exist.

    • %001: Odd parity.

    • %011: Even parity.

    • %101: No parity check, bit #7 is always 1.

    • %111: No parity check, bit #7 is always 0.

$0295-$0296
661-662

Default value of RS232 output timer, based on baud rate. (Must be filled with actual value before RS232 input/output if baud rate is "user specified" in RS232 control register, memory address $0293.)

$0297
663

Value of ST variable, device status for RS232 input/output. Bits:

  • Bit #0: 1 = Parity error occurred.

  • Bit #1: 1 = Frame error, a stop bit with the value of 0, occurred.

  • Bit #2: 1 = Input buffer underflow occurred, too much data has arrived but it has not been read from the buffer in time.

  • Bit #3: 1 = Input buffer is empty, nothing to read.

  • Bit #4: 0 = Sender is Clear To Send; 1 = Sender is not ready to send data to receiver.

  • Bit #6: 0 = Receiver reports Data Set Ready; 1 = Receiver is not ready to receive data.

  • Bit #7: 1 = Carrier loss, a stop bit and a data byte both with the value of 0, detected.

$0298
664

RS232 byte size, number of data bits per data byte, default value for bit counters.

$0299-$029A
665-666

Default value of RS232 input timer, based on baud rate. (Calculated automatically from default value of RS232 output timer, at memory address $0295-$0296.)

$029B
667

Offset of byte received in RS232 input buffer.

$029C
668

Offset of current byte in RS232 input buffer.

$029D
669

Offset of byte to send in RS232 output buffer.

$029E
670

Offset of current byte in RS232 output buffer.

$029F-$02A0
671-672

Temporary area for saving pointer to original interrupt service routine during datasette input output. Values:

  • $0000-$00FF: No datasette input/output took place yet or original pointer has been already restored.

  • $0100-$FFFF: Original pointer, datasette input/output currently in progress.

$02A1
673

Temporary area for saving original value of CIA#2 interrupt control register, at memory address $DD0D, during RS232 input/output.

$02A2
674

Temporary area for saving original value of CIA#1 timer #1 control register, at memory address $DC0E, during datasette input/output.

$02A3-$02A4
675-676

Unknown.

$02A5
677

Number of line currently being scrolled during scrolling the screen.

$02A6
678

PAL/NTSC switch, for selecting RS232 baud rate from the proper table. Values:

  • $00: NTSC.

  • $01: PAL.

$02A7-$02FF
679-767

Unused (89 bytes).

$0300-$03FF, 768-1023
$0300-$0301
768-769

Execution address of warm reset, displaying optional BASIC error message and entering BASIC idle loop.
Default: $E38B.

$0302-$0303
770-771

Execution address of BASIC idle loop.
Default: $A483.

$0304-$0305
772-773

Execution address of BASIC line tokenizater routine.
Default: $A57C.

$0306-$0307
774-775

Execution address of BASIC token decoder routine.
Default: $A71A.

$0308-$0309
776-777

Execution address of BASIC instruction executor routine.
Default: $A7E4.

$030A-$030B
778-779

Execution address of routine reading next item of BASIC expression.
Default: $AE86.

$030C
780

Default value of register A for SYS.
Value of register A after SYS.

$030D
781

Default value of register X for SYS.
Value of register X after SYS.

$030E
782

Default value of register Y for SYS.
Value of register Y after SYS.

$030F
783

Default value of status register for SYS.
Value of status register after SYS.

$0310-$0312
784-786

JMP ABS machine instruction, jump to USR() function.
$0311-$0312, 785-786: Execution address of USR() function.

$0313
787

Unused.

$0314-$0315
788-789

Execution address of interrupt service routine.
Default: $EA31.

$0316-$0317
790-791

Execution address of BRK service routine.
Default: $FE66.

$0318-$0319
792-793

Execution address of non-maskable interrupt service routine.
Default: $FE47.

$031A-$031B
794-795

Execution address of OPEN, routine opening files.
Default: $F34A.

$031C-$031D
796-797

Execution address of CLOSE, routine closing files.
Default: $F291.

$031E-$031F
798-799

Execution address of CHKIN, routine defining file as default input.
Default: $F20E.

$0320-$0321
800-801

Execution address of CHKOUT, routine defining file as default output.
Default: $F250.

$0322-$0323
802-803

Execution address of CLRCHN, routine initializating input/output.
Default: $F333.

$0324-$0325
804-805

Execution address of CHRIN, data input routine, except for keyboard and RS232 input.
Default: $F157.

$0326-$0327
806-807

Execution address of CHROUT, general purpose data output routine.
Default: $F1CA.

$0328-$0329
808-809

Execution address of STOP, routine checking the status of Stop key indicator, at memory address $0091.
Default: $F6ED.

$032A-$032B
810-811

Execution address of GETIN, general purpose data input routine.
Default: $F13E.

$032C-$032D
812-813

Execution address of CLALL, routine initializing input/output and clearing all file assignment tables.
Default: $F32F.

$032E-$032F
814-815

Unused.
Default: $FE66.

$0330-$0331
816-817

Execution address of LOAD, routine loading files.
Default: $F4A5.

$0332-$0333
818-819

Execution address of SAVE, routine saving files.
Default: $F5ED.

$0334-$033B
820-827

Unused (8 bytes).

$033C-$03FB
828-1019

Datasette buffer (192 bytes).

$03FC-$03FF
1020-1023

Unused (4 bytes).

$0400-$07FF, 1024-2047
Default screen memory
$0400-$07E7
1024-2023

Default area of screen memory (1000 bytes).

$07E8-$07F7
2024-2039

Unused (16 bytes).

$07F8-$07FF
2040-2047

Default area for sprite pointers (8 bytes).

$0800-$9FFF, 2048-40959
BASIC area
$0800
2048

Unused. (Must contain a value of 0 so that the BASIC program can be RUN.)

$0801-$9FFF
2049-40959

Default BASIC area (38911 bytes).

$8000-$9FFF
32768-40959

Optional cartridge ROM (8192 bytes).
$8000-$8001, 32768-32769: Execution address of cold reset.
$8002-$8003, 32770-32771: Execution address of non-maskable interrupt service routine.
$8004-$8008, 32772-32776: Cartridge signature. If contains the uppercase PETSCII string "CBM80" ($C3,$C2,$CD,$38,$30) then the routine vectors are accepted by the KERNAL.

$A000-$BFFF, 40960-49151
BASIC ROM
$A000-$BFFF
40960-49151

BASIC ROM or RAM area (8192 bytes); depends on the value of bits #0-#2 of the processor port at memory address $0001:

  • %x00, %x01 or %x10: RAM area.

  • %x11: BASIC ROM.

$C000-$CFFF, 49152-53247
Upper RAM area
$C000-$CFFF
49152-53247

Upper RAM area (4096 bytes).

$D000-$DFFF, 53248-57343
I/O Area
$D000-$DFFF
53248-57343

I/O Area (memory mapped chip registers), Character ROM or RAM area (4096 bytes); depends on the value of bits #0-#2 of the processor port at memory address $0001:

  • %x00: RAM area.

  • %0xx: Character ROM. (Except for the value %000, see above.)

  • %1xx: I/O Area. (Except for the value %100, see above.)

$D000-$DFFF, 53248-57343
Character ROM
$D000-$DFFF
53248-57343

Character ROM, shape of characters (4096 bytes).

$D000-$D7FF
53248-55295

Shape of characters in uppercase/graphics character set (2048 bytes, 256 entries).

$D800-$DFFF
55295-57343

Shape of characters in lowercase/uppercase character set (2048 bytes, 256 entries).

$D000-$D3FF, 53248-54271
VIC-II; video display
$D000
53248

Sprite #0 X-coordinate (only bits #0-#7).

$D001
53249

Sprite #0 Y-coordinate.

$D002
53250

Sprite #1 X-coordinate (only bits #0-#7).

$D003
53251

Sprite #1 Y-coordinate.

$D004
53252

Sprite #2 X-coordinate (only bits #0-#7).

$D005
53253

Sprite #2 Y-coordinate.

$D006
53254

Sprite #3 X-coordinate (only bits #0-#7).

$D007
53255

Sprite #3 Y-coordinate.

$D008
53256

Sprite #4 X-coordinate (only bits #0-#7).

$D009
53257

Sprite #4 Y-coordinate.

$D00A
53258

Sprite #5 X-coordinate (only bits #0-#7).

$D00B
53259

Sprite #5 Y-coordinate.

$D00C
53260

Sprite #6 X-coordinate (only bits #0-#7).

$D00D
53261

Sprite #6 Y-coordinate.

$D00E
53262

Sprite #7 X-coordinate (only bits #0-#7).

$D00F
53263

Sprite #7 Y-coordinate.

$D010
53264

Sprite #0-#7 X-coordinates (bit #8). Bits:

  • Bit #x: Sprite #x X-coordinate bit #8.

$D011
53265

Screen control register #1. Bits:

  • Bits #0-#2: Vertical raster scroll.

  • Bit #3: Screen height; 0 = 24 rows; 1 = 25 rows.

  • Bit #4: 0 = Screen off, complete screen is covered by border; 1 = Screen on, normal screen contents are visible.

  • Bit #5: 0 = Text mode; 1 = Bitmap mode.

  • Bit #6: 1 = Extended background mode on.

  • Bit #7: Read: Current raster line (bit #8).
    Write: Raster line to generate interrupt at (bit #8).

Default: $1B, %00011011.

$D012
53266

Read: Current raster line (bits #0-#7).
Write: Raster line to generate interrupt at (bits #0-#7).

$D013
53267

Light pen X-coordinate (bits #1-#8).
Read-only.

$D014
53268

Light pen Y-coordinate.
Read-only.

$D015
53269

Sprite enable register. Bits:

  • Bit #x: 1 = Sprite #x is enabled, drawn onto the screen.

$D016
53270

Screen control register #2. Bits:

  • Bits #0-#2: Horizontal raster scroll.

  • Bit #3: Screen width; 0 = 38 columns; 1 = 40 columns.

  • Bit #4: 1 = Multicolor mode on.

Default: $C8, %11001000.

$D017
53271

Sprite double height register. Bits:

  • Bit #x: 1 = Sprite #x is stretched to double height.

$D018
53272

Memory setup register. Bits:

  • Bits #1-#3: In text mode, pointer to character memory (bits #11-#13), relative to VIC bank, memory address $DD00. Values:

    • %000, 0: $0000-$07FF, 0-2047.

    • %001, 1: $0800-$0FFF, 2048-4095.

    • %010, 2: $1000-$17FF, 4096-6143.

    • %011, 3: $1800-$1FFF, 6144-8191.

    • %100, 4: $2000-$27FF, 8192-10239.

    • %101, 5: $2800-$2FFF, 10240-12287.

    • %110, 6: $3000-$37FF, 12288-14335.

    • %111, 7: $3800-$3FFF, 14336-16383.

    Values %010 and %011 in VIC bank #0 and #2 select Character ROM instead.
    In bitmap mode, pointer to bitmap memory (bit #13), relative to VIC bank, memory address $DD00. Values:

    • %0xx, 0: $0000-$1FFF, 0-8191.

    • %1xx, 4: $2000-$3FFF, 8192-16383.

  • Bits #4-#7: Pointer to screen memory (bits #10-#13), relative to VIC bank, memory address $DD00. Values:

    • %0000, 0: $0000-$03FF, 0-1023.

    • %0001, 1: $0400-$07FF, 1024-2047.

    • %0010, 2: $0800-$0BFF, 2048-3071.

    • %0011, 3: $0C00-$0FFF, 3072-4095.

    • %0100, 4: $1000-$13FF, 4096-5119.

    • %0101, 5: $1400-$17FF, 5120-6143.

    • %0110, 6: $1800-$1BFF, 6144-7167.

    • %0111, 7: $1C00-$1FFF, 7168-8191.

    • %1000, 8: $2000-$23FF, 8192-9215.

    • %1001, 9: $2400-$27FF, 9216-10239.

    • %1010, 10: $2800-$2BFF, 10240-11263.

    • %1011, 11: $2C00-$2FFF, 11264-12287.

    • %1100, 12: $3000-$33FF, 12288-13311.

    • %1101, 13: $3400-$37FF, 13312-14335.

    • %1110, 14: $3800-$3BFF, 14336-15359.

    • %1111, 15: $3C00-$3FFF, 15360-16383.

$D019
53273

Interrupt status register. Read bits:

  • Bit #0: 1 = Current raster line is equal to the raster line to generate interrupt at.

  • Bit #1: 1 = Sprite-background collision occurred.

  • Bit #2: 1 = Sprite-sprite collision occurred.

  • Bit #3: 1 = Light pen signal arrived.

  • Bit #7: 1 = An event (or more events), that may generate an interrupt, occurred and it has not been (not all of them have been) acknowledged yet.

Write bits:

  • Bit #0: 1 = Acknowledge raster interrupt.

  • Bit #1: 1 = Acknowledge sprite-background collision interrupt.

  • Bit #2: 1 = Acknowledge sprite-sprite collision interrupt.

  • Bit #3: 1 = Acknowledge light pen interrupt.

$D01A
53274

Interrupt control register. Bits:

  • Bit #0: 1 = Raster interrupt enabled.

  • Bit #1: 1 = Sprite-background collision interrupt enabled.

  • Bit #2: 1 = Sprite-sprite collision interrupt enabled.

  • Bit #3: 1 = Light pen interrupt enabled.

$D01B
53275

Sprite priority register. Bits:

  • Bit #x: 0 = Sprite #x is drawn in front of screen contents; 1 = Sprite #x is behind screen contents.

$D01C
53276

Sprite multicolor mode register. Bits:

  • Bit #x: 0 = Sprite #x is single color; 1 = Sprite #x is multicolor.

$D01D
53277

Sprite double width register. Bits:

  • Bit #x: 1 = Sprite #x is stretched to double width.

$D01E
53278

Sprite-sprite collision register. Read bits:

  • Bit #x: 1 = Sprite #x collided with another sprite.

Write: Enable further detection of sprite-sprite collisions.

$D01F
53279

Sprite-background collision register. Read bits:

  • Bit #x: 1 = Sprite #x collided with background.

Write: Enable further detection of sprite-background collisions.

$D020
53280

Border color (only bits #0-#3).

$D021
53281

Background color (only bits #0-#3).

$D022
53282

Extra background color #1 (only bits #0-#3).

$D023
53283

Extra background color #2 (only bits #0-#3).

$D024
53284

Extra background color #3 (only bits #0-#3).

$D025
53285

Sprite extra color #1 (only bits #0-#3).

$D026
53286

Sprite extra color #1 (only bits #0-#3).

$D027
53287

Sprite #0 color (only bits #0-#3).

$D028
53288

Sprite #1 color (only bits #0-#3).

$D029
53289

Sprite #2 color (only bits #0-#3).

$D02A
53290

Sprite #3 color (only bits #0-#3).

$D02B
53291

Sprite #4 color (only bits #0-#3).

$D02C
53292

Sprite #5 color (only bits #0-#3).

$D02D
53293

Sprite #6 color (only bits #0-#3).

$D02E
53294

Sprite #7 color (only bits #0-#3).

$D02F-$D03F
53295-53311

Unusable (17 bytes).

$D040-$D3FF
53312-54271

VIC-II register images (repeated every $40, 64 bytes).

$D400-$D7FF, 54272-55295
SID; audio
$D400-$D401
54272-54273

Voice #1 frequency.
Write-only.

$D402-$D403
54274-54275

Voice #1 pulse width.
Write-only.

$D404
54276

Voice #1 control register. Bits:

  • Bit #0: 0 = Voice off, Release cycle; 1 = Voice on, Attack-Decay-Sustain cycle.

  • Bit #1: 1 = Synchronization enabled.

  • Bit #2: 1 = Ring modulation enabled.

  • Bit #3: 1 = Disable voice, reset noise generator.

  • Bit #4: 1 = Triangle waveform enabled.

  • Bit #5: 1 = Saw waveform enabled.

  • Bit #6: 1 = Rectangle waveform enabled.

  • Bit #7: 1 = Noise enabled.

Write-only.

$D405
54277

Voice #1 Attack and Decay length. Bits:

  • Bits #0-#3: Decay length. Values:

    • %0000, 0: 6 ms.

    • %0001, 1: 24 ms.

    • %0010, 2: 48 ms.

    • %0011, 3: 72 ms.

    • %0100, 4: 114 ms.

    • %0101, 5: 168 ms.

    • %0110, 6: 204 ms.

    • %0111, 7: 240 ms.

    • %1000, 8: 300 ms.

    • %1001, 9: 750 ms.

    • %1010, 10: 1.5 s.

    • %1011, 11: 2.4 s.

    • %1100, 12: 3 s.

    • %1101, 13: 9 s.

    • %1110, 14: 15 s.

    • %1111, 15: 24 s.

  • Bits #4-#7: Attack length. Values:

    • %0000, 0: 2 ms.

    • %0001, 1: 8 ms.

    • %0010, 2: 16 ms.

    • %0011, 3: 24 ms.

    • %0100, 4: 38 ms.

    • %0101, 5: 56 ms.

    • %0110, 6: 68 ms.

    • %0111, 7: 80 ms.

    • %1000, 8: 100 ms.

    • %1001, 9: 250 ms.

    • %1010, 10: 500 ms.

    • %1011, 11: 800 ms.

    • %1100, 12: 1 s.

    • %1101, 13: 3 s.

    • %1110, 14: 5 s.

    • %1111, 15: 8 s.

Write-only.

$D406
54278

Voice #1 Sustain volume and Release length. Bits:

  • Bits #0-#3: Release length. Values:

    • %0000, 0: 6 ms.

    • %0001, 1: 24 ms.

    • %0010, 2: 48 ms.

    • %0011, 3: 72 ms.

    • %0100, 4: 114 ms.

    • %0101, 5: 168 ms.

    • %0110, 6: 204 ms.

    • %0111, 7: 240 ms.

    • %1000, 8: 300 ms.

    • %1001, 9: 750 ms.

    • %1010, 10: 1.5 s.

    • %1011, 11: 2.4 s.

    • %1100, 12: 3 s.

    • %1101, 13: 9 s.

    • %1110, 14: 15 s.

    • %1111, 15: 24 s.

  • Bits #4-#7: Sustain volume.

Write-only.

$D407-$D408
54279-54280

Voice #2 frequency.
Write-only.

$D409-$D40A
54281-54282

Voice #2 pulse width.
Write-only.

$D40B
54283

Voice #2 control register.
Write-only.

$D40C
54284

Voice #2 Attack and Decay length.
Write-only.

$D40D
54285

Voice #2 Sustain volume and Release length.
Write-only.

$D40E-$D40F
54286-54287

Voice #3 frequency.
Write-only.

$D410-$D411
54288-54289

Voice #3 pulse width.
Write-only.

$D412
54290

Voice #3 control register.
Write-only.

$D413
54291

Voice #3 Attack and Decay length.
Write-only.

$D414
54292

Voice #3 Sustain volume and Release length.
Write-only.

$D415
54293

Filter cut off frequency (bits #0-#2).
Write-only.

$D416
54294

Filter cut off frequency (bits #3-#10).
Write-only.

$D417
54295

Filter control. Bits:

  • Bit #0: 1 = Voice #1 filtered.

  • Bit #1: 1 = Voice #2 filtered.

  • Bit #2: 1 = Voice #3 filtered.

  • Bit #3: 1 = External voice filtered.

  • Bits #4-#7: Filter resonance.

Write-only.

$D418
54296

Volume and filter modes. Bits:

  • Bits #0-#3: Volume.

  • Bit #4: 1 = Low pass filter enabled.

  • Bit #5: 1 = Band pass filter enabled.

  • Bit #6: 1 = High pass filter enabled.

  • Bit #7: 1 = Voice #3 disabled.

Write-only.

$D419
54297

X value of paddle selected at memory address $DD00. (Updates at every 512 system cycles.)
Read-only.

$D41A
54298

Y value of paddle selected at memory address $DD00. (Updates at every 512 system cycles.)
Read-only.

$D41B
54299

Voice #3 waveform output.
Read-only.

$D41C
54300

Voice #3 ADSR output.
Read-only.

$D41D-$D41F
54301-54303

Unusable (3 bytes).

$D420-$D7FF
54304-55295

SID register images (repeated every $20, 32 bytes).

$D800-$DBFF, 55296-56319
Color RAM
$D800-$DBE7
55296-56295

Color RAM (1000 bytes, only bits #0-#3).

$DBE8-$DBFF
56296-56319

Unused (24 bytes, only bits #0-#3).

$DC00-$DCFF, 56320-56575
CIA#1; inputs (keyboard, joystick, mouse), datasette, IRQ control
$DC00
56320

Port A, keyboard matrix columns and joystick #2. Read bits:

  • Bit #0: 0 = Port 2 joystick up pressed.

  • Bit #1: 0 = Port 2 joystick down pressed.

  • Bit #2: 0 = Port 2 joystick left pressed.

  • Bit #3: 0 = Port 2 joystick right pressed.

  • Bit #4: 0 = Port 2 joystick fire pressed.

Write bits:

  • Bit #x: 0 = Select keyboard matrix column #x.

  • Bits #6-#7: Paddle selection; %01 = Paddle #1; %10 = Paddle #2.

$DC01
56321

Port B, keyboard matrix rows and joystick #1. Bits:

  • Bit #x: 0 = A key is currently being pressed in keyboard matrix row #x, in the column selected at memory address $DC00.

  • Bit #0: 0 = Port 1 joystick up pressed.

  • Bit #1: 0 = Port 1 joystick down pressed.

  • Bit #2: 0 = Port 1 joystick left pressed.

  • Bit #3: 0 = Port 1 joystick right pressed.

  • Bit #4: 0 = Port 1 joystick fire pressed.

$DC02
56322

Port A data direction register.

  • Bit #x: 0 = Bit #x in port A can only be read; 1 = Bit #x in port A can be read and written.

$DC03
56323

Port B data direction register.

  • Bit #x: 0 = Bit #x in port B can only be read; 1 = Bit #x in port B can be read and written.

$DC04-$DC05
56324-56325

Timer A. Read: Current timer value.
Write: Set timer start value.

$DC06-$DC07
56326-56327

Timer B. Read: Current timer value.
Write: Set timer start value.

$DC08
56328

Time of Day, tenth seconds (in BCD). Values: $00-$09. Read: Current TOD value.
Write: Set TOD or alarm time.

$DC09
56329

Time of Day, seconds (in BCD). Values: $00-$59. Read: Current TOD value.
Write: Set TOD or alarm time.

$DC0A
56330

Time of Day, minutes (in BCD). Values: $00-$59. Read: Current TOD value.
Write: Set TOD or alarm time.

$DC0B
56331

Time of Day, hours (in BCD). Read bits:

  • Bits #0-#5: Hours.

  • Bit #7: 0 = AM; 1 = PM.

Write: Set TOD or alarm time.

$DC0C
56332

Serial shift register. (Bits are read and written upon every positive edge of the CNT pin.)

$DC0D
56333

Interrupt control and status register. Read bits:

  • Bit #0: 1 = Timer A underflow occurred.

  • Bit #1: 1 = Timer B underflow occurred.

  • Bit #2: 1 = TOD is equal to alarm time.

  • Bit #3: 1 = A complete byte has been received into or sent from serial shift register.

  • Bit #4: Signal level on FLAG pin, datasette input.

  • Bit #7: An interrupt has been generated.

Write bits:

  • Bit #0: 1 = Enable interrupts generated by timer A underflow.

  • Bit #1: 1 = Enable interrupts generated by timer B underflow.

  • Bit #2: 1 = Enable TOD alarm interrupt.

  • Bit #3: 1 = Enable interrupts generated by a byte having been received/sent via serial shift register.

  • Bit #4: 1 = Enable interrupts generated by positive edge on FLAG pin.

  • Bit #7: Fill bit; bits #0-#6, that are set to 1, get their values from this bit; bits #0-#6, that are set to 0, are left unchanged.

$DC0E
56334

Timer A control register. Bits:

  • Bit #0: 0 = Stop timer; 1 = Start timer.

  • Bit #1: 1 = Indicate timer underflow on port B bit #6.

  • Bit #2: 0 = Upon timer underflow, invert port B bit #6; 1 = upon timer underflow, generate a positive edge on port B bit #6 for 1 system cycle.

  • Bit #3: 0 = Timer restarts upon underflow; 1 = Timer stops upon underflow.

  • Bit #4: 1 = Load start value into timer.

  • Bit #5: 0 = Timer counts system cycles; 1 = Timer counts positive edges on CNT pin.

  • Bit #6: Serial shift register direction; 0 = Input, read; 1 = Output, write.

  • Bit #7: TOD speed; 0 = 60 Hz; 1 = 50 Hz.

$DC0F
56335

Timer B control register. Bits:

  • Bit #0: 0 = Stop timer; 1 = Start timer.

  • Bit #1: 1 = Indicate timer underflow on port B bit #7.

  • Bit #2: 0 = Upon timer underflow, invert port B bit #7; 1 = upon timer underflow, generate a positive edge on port B bit #7 for 1 system cycle.

  • Bit #3: 0 = Timer restarts upon underflow; 1 = Timer stops upon underflow.

  • Bit #4: 1 = Load start value into timer.

  • Bits #5-#6: %00 = Timer counts system cycles; %01 = Timer counts positive edges on CNT pin; %10 = Timer counts underflows of timer A; %11 = Timer counts underflows of timer A occurring along with a positive edge on CNT pin.

  • Bit #7: 0 = Writing into TOD registers sets TOD; 1 = Writing into TOD registers sets alarm time.

$DC10-$DCFF
56336-56575

CIA#1 register images (repeated every $10, 16 bytes).

$DD00-$DDFF, 56576-56831
CIA#2; serial bus, RS232, NMI control
$DD00
56576

Port A, serial bus access. Bits:

  • Bits #0-#1: VIC bank. Values:

    • %00, 0: Bank #3, $C000-$FFFF, 49152-65535.

    • %01, 1: Bank #2, $8000-$BFFF, 32768-49151.

    • %10, 2: Bank #1, $4000-$7FFF, 16384-32767.

    • %11, 3: Bank #0, $0000-$3FFF, 0-16383.

  • Bit #2: RS232 TXD line, output bit.

  • Bit #3: Serial bus ATN OUT; 0 = High; 1 = Low.

  • Bit #4: Serial bus CLOCK OUT; 0 = High; 1 = Low.

  • Bit #5: Serial bus DATA OUT; 0 = High; 1 = Low.

  • Bit #6: Serial bus CLOCK IN; 0 = Low; 1 = High.

  • Bit #7: Serial bus DATA IN; 0 = Low; 1 = High.

$DD01
56577

Port B, RS232 access. Read bits:

  • Bit #0: RS232 RXD line, input bit.

  • Bit #3: RS232 RI line.

  • Bit #4: RS232 DCD line.

  • Bit #5: User port H pin.

  • Bit #6: RS232 CTS line; 1 = Sender is ready to send.

  • Bit #7: RS232 DSR line; 1 = Receiver is ready to receive.

Write bits:

  • Bit #1: RS232 RTS line. 1 = Sender is ready to send.

  • Bit #2: RS232 DTR line. 1 = Receiver is ready to receive.

  • Bit #3: RS232 RI line.

  • Bit #4: RS232 DCD line.

  • Bit #5: User port H pin.

$DD02
56578

Port A data direction register.

  • Bit #x: 0 = Bit #x in port A can only be read; 1 = Bit #x in port A can be read and written.

$DD03
56579

Port B data direction register.

  • Bit #x: 0 = Bit #x in port B can only be read; 1 = Bit #x in port B can be read and written.

$DD04-$DD05
56580-56581

Timer A. Read: Current timer value.
Write: Set timer start value.

$DD06-$DD07
56582-56583

Timer B. Read: Current timer value.
Write: Set timer start value.

$DD08
56584

Time of Day, tenth seconds (in BCD). Values: $00-$09. Read: Current TOD value.
Write: Set TOD or alarm time.

$DD09
56585

Time of Day, seconds (in BCD). Values: $00-$59. Read: Current TOD value.
Write: Set TOD or alarm time.

$DD0A
56586

Time of Day, minutes (in BCD). Values: $00-$59. Read: Current TOD value.
Write: Set TOD or alarm time.

$DD0B
56587

Time of Day, hours (in BCD). Read bits:

  • Bits #0-#5: Hours.

  • Bit #7: 0 = AM; 1 = PM.

Write: Set TOD or alarm time.

$DD0C
56588

Serial shift register. (Bits are read and written upon every positive edge of the CNT pin.)

$DD0D
56589

Interrupt control and status register. Read bits:

  • Bit #0: 1 = Timer A underflow occurred.

  • Bit #1: 1 = Timer B underflow occurred.

  • Bit #2: 1 = TOD is equal to alarm time.

  • Bit #3: 1 = A complete byte has been received into or sent from serial shift register.

  • Bit #4: Signal level on FLAG pin.

  • Bit #7: A non-maskable interrupt has been generated.

Write bits:

  • Bit #0: 1 = Enable non-maskable interrupts generated by timer A underflow.

  • Bit #1: 1 = Enable non-maskable interrupts generated by timer B underflow.

  • Bit #2: 1 = Enable TOD alarm non-maskable interrupt.

  • Bit #3: 1 = Enable non-maskable interrupts generated by a byte having been received/sent via serial shift register.

  • Bit #4: 1 = Enable non-maskable interrupts generated by positive edge on FLAG pin.

  • Bit #7: Fill bit; bits #0-#6, that are set to 1, get their values from this bit; bits #0-#6, that are set to 0, are left unchanged.

$DD0E
56590

Timer A control register. Bits:

  • Bit #0: 0 = Stop timer; 1 = Start timer.

  • Bit #1: 1 = Indicate timer underflow on port B bit #6.

  • Bit #2: 0 = Upon timer underflow, invert port B bit #6; 1 = upon timer underflow, generate a positive edge on port B bit #6 for 1 system cycle.

  • Bit #3: 0 = Timer restarts upon underflow; 1 = Timer stops upon underflow.

  • Bit #4: 1 = Load start value into timer.

  • Bit #5: 0 = Timer counts system cycles; 1 = Timer counts positive edges on CNT pin.

  • Bit #6: Serial shift register direction; 0 = Input, read; 1 = Output, write.

  • Bit #7: TOD speed; 0 = 60 Hz; 1 = 50 Hz.

$DD0F
56591

Timer B control register. Bits:

  • Bit #0: 0 = Stop timer; 1 = Start timer.

  • Bit #1: 1 = Indicate timer underflow on port B bit #7.

  • Bit #2: 0 = Upon timer underflow, invert port B bit #7; 1 = upon timer underflow, generate a positive edge on port B bit #7 for 1 system cycle.

  • Bit #3: 0 = Timer restarts upon underflow; 1 = Timer stops upon underflow.

  • Bit #4: 1 = Load start value into timer.

  • Bits #5-#6: %00 = Timer counts system cycles; %01 = Timer counts positive edges on CNT pin; %10 = Timer counts underflows of timer A; %11 = Timer counts underflows of timer A occurring along with a positive edge on CNT pin.

  • Bit #7: 0 = Writing into TOD registers sets TOD; 1 = Writing into TOD registers sets alarm time.

$DD10-$DDFF
56592-56831

CIA#2 register images (repeated every $10, 16 bytes).

$DE00-$DEFF, 56832-57087
I/O Area #1
$DE00-$DEFF
56832-57087

I/O Area #1, memory mapped registers or machine code routines of optional external devices (256 bytes). Layout and contents depend on the actual device.

$DF00-$DFFF, 57088-57343
I/O Area #2
$DF00-$DFFF
57088-57343

I/O Area #2, memory mapped registers or machine code routines of optional external devices (256 bytes). Layout and contents depend on the actual device.

$E000-$FFFF, 57344-65535
KERNAL ROM
$E000-$FFFF
57344-65535

KERNAL ROM or RAM area (8192 bytes); depends on the value of bits #0-#2 of the processor port at memory address $0001:

  • %x0x: RAM area.

  • %x1x: KERNAL ROM.

$FFFA-$FFFF, 65530-65535
Hardware vectors
$FFFA-$FFFB
65530-65531

Execution address of non-maskable interrupt service routine.
Default: $FE43.

$FFFC-$FFFD
65532-65533

Execution address of cold reset.
Default: $FCE2.

$FFFE-$FFFF
65534-65535

Execution address of interrupt service routine.
Default: $FF48.