$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.)

$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-$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-$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-$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

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 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 (4096 bytes).

$D000-$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, 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

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 #2 (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).

$D400-$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).

$D800-$DBE7

55296-56295

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

$DBE8-$DBFF

56296-56319

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

$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

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, 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, 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 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.

$FF81

65409

SCINIT
Initialize VIC; restore default input/output to keyboard/screen; clear screen; set PAL/NTSC switch and interrupt timer.
Input: –
Output: –
Used registers: A, X, Y.
Real address: $FF5B.

$FF84

65412

IOINIT
Initialize CIA's, SID volume; setup memory configuration; set and start interrupt timer.
Input: –
Output: –
Used registers: A, X.
Real address: $FDA3.

$FF87

65415

RAMTAS
Clear memory addresses $0002-$0101 and $0200-$03FF; run memory test and set start and end address of BASIC work area accordingly; set screen memory to $0400 and datasette buffer to $033C.
Input: –
Output: –
Used registers: A, X, Y.
Real address: $FD50.

$FF8A

65418

RESTOR
Fill vector table at memory addresses $0314-$0333 with default values.
Input: –
Output: –
Used registers: –
Real address: $FD15.

$FF8D

65421

VECTOR
Copy vector table at memory addresses $0314-$0333 from or into user table.
Input: Carry: 0 = Copy user table into vector table, 1 = Copy vector table into user table; X/Y = Pointer to user table.
Output: –
Used registers: A, Y.
Real address: $FD1A.

$FF90

65424

SETMSG
Set system error display switch at memory address $009D.
Input: A = Switch value.
Output: –
Used registers: –
Real address: $FE18.

$FF93

65427

LSTNSA
Send LISTEN secondary address to serial bus. (Must call LISTEN beforehands.)
Input: A = Secondary address.
Output: –
Used registers: A.
Real address: $EDB9.

$FF96

65430

TALKSA
Send TALK secondary address to serial bus. (Must call TALK beforehands.)
Input: A = Secondary address.
Output: –
Used registers: A.
Real address: $EDC7.

$FF99

65433

MEMBOT
Save or restore start address of BASIC work area.
Input: Carry: 0 = Restore from input, 1 = Save to output; X/Y = Address (if Carry = 0).
Output: X/Y = Address (if Carry = 1).
Used registers: X, Y.
Real address: $FE25.

$FF9C

65436

MEMTOP
Save or restore end address of BASIC work area.
Input: Carry: 0 = Restore from input, 1 = Save to output; X/Y = Address (if Carry = 0).
Output: X/Y = Address (if Carry = 1).
Used registers: X, Y.
Real address: $FE34.

$FF9F

65439

SCNKEY
Query keyboard; put current matrix code into memory address $00CB, current status of shift keys into memory address $028D and PETSCII code into keyboard buffer.
Input: –
Output: –
Used registers: A, X, Y.
Real address: $EA87.

$FFA2

65442

SETTMO
Unknown. (Set serial bus timeout.)
Input: A = Timeout value.
Output: –
Used registers: –
Real address: $FE21.

$FFA5

65445

IECIN
Read byte from serial bus. (Must call TALK and TALKSA beforehands.)
Input: –
Output: A = Byte read.
Used registers: A.
Real address: $EE13.

$FFA8

65448

IECOUT
Write byte to serial bus. (Must call LISTEN and LSTNSA beforehands.)
Input: A = Byte to write.
Output: –
Used registers: –
Real address: $EDDD.

$FFAB

65451

UNTALK
Send UNTALK command to serial bus.
Input: –
Output: –
Used registers: A.
Real address: $EDEF.

$FFAE

65454

UNLSTN
Send UNLISTEN command to serial bus.
Input: –
Output: –
Used registers: A.
Real address: $EDFE.

$FFB1

65457

LISTEN
Send LISTEN command to serial bus.
Input: A = Device number.
Output: –
Used registers: A.
Real address: $ED0C.

$FFB4

65460

TALK
Send TALK command to serial bus.
Input: A = Device number.
Output: –
Used registers: A.
Real address: $ED09.

$FFB7

65463

READST
Fetch status of current input/output device, value of ST variable. (For RS232, status is cleared.)
Input: –
Output: A = Device status.
Used registers: A.
Real address: $FE07.

$FFBA

65466

SETLFS
Set file parameters.
Input: A = Logical number; X = Device number; Y = Secondary address.
Output: –
Used registers: –
Real address: $FE00.

$FFBD

65469

SETNAM
Set file name parameters.
Input: A = File name length; X/Y = Pointer to file name.
Output: –
Used registers: –
Real address: $FDF9.

$FFC0

65472

OPEN
Open file. (Must call SETLFS and SETNAM beforehands.)
Input: –
Output: –
Used registers: A, X, Y.
Real address: ($031A), $F34A.

$FFC3

65475

CLOSE
Close file.
Input: A = Logical number.
Output: –
Used registers: A, X, Y.
Real address: ($031C), $F291.

$FFC6

65478

CHKIN
Define file as default input. (Must call OPEN beforehands.)
Input: X = Logical number.
Output: –
Used registers: A, X.
Real address: ($031E), $F20E.

$FFC9

65481

CHKOUT
Define file as default output. (Must call OPEN beforehands.)
Input: X = Logical number.
Output: –
Used registers: A, X.
Real address: ($0320), $F250.

$FFCC

65484

CLRCHN
Close default input/output files (for serial bus, send UNTALK and/or UNLISTEN); restore default input/output to keyboard/screen.
Input: –
Output: –
Used registers: A, X.
Real address: ($0322), $F333.

$FFCF

65487

CHRIN
Read byte from default input (for keyboard, read a line from the screen). (If not keyboard, must call OPEN and CHKIN beforehands.)
Input: –
Output: A = Byte read.
Used registers: A, Y.
Real address: ($0324), $F157.

$FFD2

65490

CHROUT
Write byte to default output. (If not screen, must call OPEN and CHKOUT beforehands.)
Input: A = Byte to write.
Output: –
Used registers: –
Real address: ($0326), $F1CA.

$FFD5

65493

LOAD
Load or verify file. (Must call SETLFS and SETNAM beforehands.)
Input: A: 0 = Load, 1-255 = Verify; X/Y = Load address (if secondary address = 0).
Output: Carry: 0 = No errors, 1 = Error; A = KERNAL error code (if Carry = 1); X/Y = Address of last byte loaded/verified (if Carry = 0).
Used registers: A, X, Y.
Real address: $F49E.

$FFD8

65496

SAVE
Save file. (Must call SETLFS and SETNAM beforehands.)
Input: A = Address of zero page register holding start address of memory area to save; X/Y = End address of memory area plus 1.
Output: Carry: 0 = No errors, 1 = Error; A = KERNAL error code (if Carry = 1).
Used registers: A, X, Y.
Real address: $F5DD.

$FFDB

65499

SETTIM
Set Time of Day, at memory address $00A0-$00A2.
Input: A/X/Y = New TOD value.
Output: –
Used registers: –
Real address: $F6E4.

$FFDE

65502

RDTIM
Read Time of Day, at memory address $00A0-$00A2.
Input: –
Output: A/X/Y = Current TOD value.
Used registers: A, X, Y.
Real address: $F6DD.

$FFE1

65505

STOP
Query Stop key indicator, at memory address $0091; if pressed, call CLRCHN and clear keyboard buffer.
Input: –
Output: Zero: 0 = Not pressed, 1 = Pressed; Carry: 1 = Pressed.
Used registers: A, X.
Real address: ($0328), $F6ED.

$FFE4

65508

GETIN
Read byte from default input. (If not keyboard, must call OPEN and CHKIN beforehands.)
Input: –
Output: A = Byte read.
Used registers: A, X, Y.
Real address: ($032A), $F13E.

$FFE7

65511

CLALL
Clear file table; call CLRCHN.
Input: –
Output: –
Used registers: A, X.
Real address: ($032C), $F32F.

$FFEA

65514

UDTIM
Update Time of Day, at memory address $00A0-$00A2, and Stop key indicator, at memory address $0091.
Input: –
Output: –
Used registers: A, X.
Real address: $F69B.

$FFED

65517

SCREEN
Fetch number of screen rows and columns.
Input: –
Output: X = Number of columns (40); Y = Number of rows (25).
Used registers: X, Y.
Real address: $E505.

$FFF0

65520

PLOT
Save or restore cursor position.
Input: Carry: 0 = Restore from input, 1 = Save to output; X = Cursor column (if Carry = 0); Y = Cursor row (if Carry = 0).
Output: X = Cursor column (if Carry = 1); Y = Cursor row (if Carry = 1).
Used registers: X, Y.
Real address: $E50A.

$FFF3

65523

IOBASE
Fetch CIA #1 base address.
Input: –
Output: X/Y = CIA #1 base address ($DC00).
Used registers: X, Y.
Real address: $E500.

$FFFA-$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.