Commodore 64 memory map

Address Hex Address Dec Description

$0000-$00FF, 0-256

Zero page

$0000 0 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. Processor port data direction register. Bits:Default: $2F, %00101111.

$0001 1 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. Processor port. Bits: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 $00: LOAD.

$01-$FF: VERIFY. LOAD/VERIFY switch. Values:

$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 $00: Operation was not called by DIM.

$40-$7F: Operation was called by DIM. Switch for array operations. Values:

$000D 13 $00: Numerical.

$FF: String. Current expression type. Values:

$000E 14 Bit #7: 0 = Floating point; 1 = Integer. Current numerical expression type. Bits:

$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 $00: Integer variables are accepted.

$01-$FF: Integer variables are not accepted. Switch during fetch of variable name. Values:

$0011 17 $00: INPUT.

$40: GET.

$98: READ. GET/INPUT/READ switch. Values:

$0012 18 $00: Positive.

$FF: Negative. Sign during SIN() and TAN(). Values:

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

$FF00-$FFFF: Direct mode, no BASIC program is being executed. Current BASIC line number. Values:

$003B-$003C 59-60 Current BASIC line number for CONT.

$003D-$003E 61-62 $0000-$00FF: CONT'ing is not possible.

$0100-$FFFF: Pointer to next BASIC instruction. Pointer to next BASIC instruction for CONT. Values:

$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 $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.

Name and type of current variable. Bits:

$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 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. Comparison operator indicator. Bits:

$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 Bit #7: 0 = Positive; 1 = Negative. Sign of FAC. Bits:

$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 Bit #7: 0 = Positive; 1 = Negative. Sign of ARG. Bits:

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

$0091 145 $7F: Stop key is pressed.

$FF: Stop key is not pressed. Stop key indicator. Values:

$0092 146 Unknown. (Timing constant during datasette input.)

$0093 147 $00: LOAD.

$01-$FF: VERIFY. LOAD/VERIFY switch. Values:

$0094 148 Bit #7: 1 = Output cache dirty, must transfer cache contents upon next output to serial bus. Serial bus output cache status. Bits:

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

Bit #7: 0 = Suppress system messages; 1 = Display them. System error display switch. Bits:

$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 Bit #7: 0 = Send byte right after handshake; 1 = Do EOI delay first. Bit counter during datasette output. EOI switch during serial bus output. Bits: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 $00: Data bit.

$01-$FF: Stop bit. Stop bit switch during RS232 input. Values:

$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 Bits #0-#6: Bit count.

Bit #7: 0 = Data bit; 1 = Stop bit. Bit counter during datasette input/output. Bit counter and stop bit switch during RS232 output. Bits: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 $00: No parameter.

$01-$FF: Parameter length. Length of file name or disk command; first parameter of LOAD, SAVE and VERIFY or fourth parameter of OPEN. Values:

$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 $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. Datasette motor switch. Values:

$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 $00-$3F: Keyboard matrix code.

$40: No key was pressed at the time of previous check. Matrix code of key previously pressed. Values:

$00C6 198 $00, 0: Buffer is empty.

$01-$0A, 1-10: Buffer length. Length of keyboard buffer. Values:

$00C7 199 $00: Normal mode.

$12: Reverse mode. Reverse mode switch. Values:

$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 $00-$3F: Keyboard matrix code.

$40: No key is currently pressed. Matrix code of key currently being pressed. Values:

$00CC 204 $00: Cursor is on.

$01-$FF: Cursor is off. Cursor visibility switch. Values:

$00CD 205 $00, 0: Must change cursor phase.

$01-$14, 1-20: Delay. Delay counter for changing cursor phase. Values:

$00CE 206 Screen code of character under cursor.

$00CF 207 $00: Cursor off phase, original character visible.

$01: Cursor on phase, reverse character visible. Cursor phase switch. Values:

$00D0 208 $00: Return character reached, end of line.

$01-$FF: Still reading characters from line. End of line switch during screen input. Values:

$00D1-$00D2 209-210 Pointer to current line in screen memory.

$00D3 211 Current cursor column. Values: $00-$27, 0-39.

$00D4 212 $00: Normal mode.

$01: Quotation mode. Quotation mode switch. Values:

$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 $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. Number of insertions. Values:

$00D9-$00F1 217-241 $00-$7F: Pointer high byte.

$80-$FF: No pointer, line is an extension of previous line on screen. High byte of pointers to each line in screen memory (25 bytes). Values:

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

$0100-$FFFF: Buffer pointer. Pointer to RS232 input buffer. Values:

$00F9-$00FA 249-250 $0000-$00FF: No buffer defined, a new buffer must be allocated upon RS232 output.

$0100-$FFFF: Buffer pointer. Pointer to RS232 output buffer. Values:

$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 $00, 0: No buffer.

$01-$0F, 1-15: Buffer size. Maximum length of keyboard buffer. Values:

$028A 650 Bits #6-#7: %00 = Only cursor up/down, cursor left/right, Insert/Delete and Space repeat; %01 = No key repeats; %1x = All keys repeat. Keyboard repeat switch. Bits:

$028B 651 $00, 0: Must repeat key.

$01-$04, 1-4: Delay repetition. Delay counter during repeat sequence, for delaying between successive repeats. Values:

$028C 652 $00, 0: Must start repeat sequence.

$01-$10, 1-16: Delay repeat sequence. Repeat sequence delay counter, for delaying before first repetition. Values:

$028D 653 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. Shift key indicator. Bits:

$028E 654 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. Previous value of shift key indicator. Bits:

$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 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. Commodore-Shift switch. Bits:

$0292 658 $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. Scroll direction switch during scrolling the screen. Values:

$0293 659 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. RS232 control register. Bits:

$0294 660 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.

RS232 command register. Bits:

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

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

$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 $00: NTSC.

$01: PAL. PAL/NTSC switch, for selecting RS232 baud rate from the proper table. Values:

$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 %x00, %x01 or %x10: RAM area.

%x11: BASIC ROM. BASIC ROM or RAM area (8192 bytes); depends on the value of bits #0-#2 of the processor port at memory address $0001:

$C000-$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 %x00: RAM area.

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

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

$D000-$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 Bit #x: Sprite #x X-coordinate bit #8. Sprite #0-#7 X-coordinates (bit #8). Bits:

$D011 53265 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. Screen control register #1. Bits: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 Bit #x: 1 = Sprite #x is enabled, drawn onto the screen. Sprite enable register. Bits:

$D016 53270 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. Screen control register #2. Bits:Default: $C8, %11001000.

$D017 53271 Bit #x: 1 = Sprite #x is stretched to double height. Sprite double height register. Bits:

$D018 53272 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.

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: 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.

Memory setup register. Bits:

$D019 53273 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. Interrupt status register. Read bits:Write bits:

$D01A 53274 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. Interrupt control register. Bits:

$D01B 53275 Bit #x: 0 = Sprite #x is drawn in front of screen contents; 1 = Sprite #x is behind screen contents. Sprite priority register. Bits:

$D01C 53276 Bit #x: 0 = Sprite #x is single color; 1 = Sprite #x is multicolor. Sprite multicolor mode register. Bits:

$D01D 53277 Bit #x: 1 = Sprite #x is stretched to double width. Sprite double width register. Bits:

$D01E 53278 Bit #x: 1 = Sprite #x collided with another sprite. Write: Enable further detection of sprite-sprite collisions. Sprite-sprite collision register. Read bits:Write: Enable further detection of sprite-sprite collisions.

$D01F 53279 Bit #x: 1 = Sprite #x collided with background. Write: Enable further detection of sprite-background collisions. Sprite-background collision register. Read bits: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).

$D400-$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 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. Voice #1 control register. Bits:Write-only.

$D405 54277 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. Voice #1 Attack and Decay length. Bits:Write-only.

$D406 54278 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. Voice #1 Sustain volume and Release length. Bits: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 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. Filter control. Bits:Write-only.

$D418 54296 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. Volume and filter modes. Bits: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 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. Port A, keyboard matrix columns and joystick #2. Read bits:Write bits:

$DC01 56321 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. Port B, keyboard matrix rows and joystick #1. Bits:

$DC02 56322 Bit #x: 0 = Bit #x in port A can only be read; 1 = Bit #x in port A can be read and written. Port A data direction register.

$DC03 56323 Bit #x: 0 = Bit #x in port B can only be read; 1 = Bit #x in port B can be read and written. Port B data direction register.

$DC04-$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 Bits #0-#5: Hours.

Bit #7: 0 = AM; 1 = PM. Write: Set TOD or alarm time. Time of Day, hours (in BCD). Read bits: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 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. Interrupt control and status register. Read bits:Write bits:

$DC0E 56334 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. Timer A control register. Bits:

$DC0F 56335 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. Timer B control register. Bits:

$DC10-$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 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. Port A, serial bus access. Bits:

$DD01 56577 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. Port B, RS232 access. Read bits:Write bits:

$DD02 56578 Bit #x: 0 = Bit #x in port A can only be read; 1 = Bit #x in port A can be read and written. Port A data direction register.

$DD03 56579 Bit #x: 0 = Bit #x in port B can only be read; 1 = Bit #x in port B can be read and written. Port B data direction register.

$DD04-$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 Bits #0-#5: Hours.

Bit #7: 0 = AM; 1 = PM. Write: Set TOD or alarm time. Time of Day, hours (in BCD). Read bits: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 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. Interrupt control and status register. Read bits:Write bits:

$DD0E 56590 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. Timer A control register. Bits:

$DD0F 56591 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. Timer B control register. Bits:

$DD10-$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 %x0x: RAM area.

%x1x: KERNAL ROM. KERNAL ROM or RAM area (8192 bytes); depends on the value of bits #0-#2 of the processor port at memory address $0001:

$FF81-$FFF3, 65409-65523

Kernal functions

$FF81 65409 SCINIT

Initialize VIC; restore default input/output to keyboard/screen; clear screen; set PAL/NTSC switch and interrupt timer.

Input: â€“

Output: â€“

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: â€“

Output: â€“

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: â€“

Output: â€“

Used registers: A, X, Y.

Real address: $FD50.

$FF8A 65418 RESTOR

Fill vector table at memory addresses $0314-$0333 with default values.

Input: â€“

Output: â€“

Used registers: â€“

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: â€“

Used registers: A, Y.

Real address: $FD1A.

$FF90 65424 SETMSG

Set system error display switch at memory address $009D.

Input: A = Switch value.

Output: â€“

Used registers: â€“

Real address: $FE18.

$FF93 65427 LSTNSA

Send LISTEN secondary address to serial bus. (Must call LISTEN beforehands.)

Input: A = Secondary address.

Output: â€“

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: â€“

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: â€“

Output: â€“

Used registers: A, X, Y.

Real address: $EA87.

$FFA2 65442 SETTMO

Unknown. (Set serial bus timeout.)

Input: A = Timeout value.

Output: â€“

Used registers: â€“

Real address: $FE21.

$FFA5 65445 IECIN

Read byte from serial bus. (Must call TALK and TALKSA beforehands.)

Input: â€“

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: â€“

Used registers: â€“

Real address: $EDDD.

$FFAB 65451 UNTALK

Send UNTALK command to serial bus.

Input: â€“

Output: â€“

Used registers: A.

Real address: $EDEF.

$FFAE 65454 UNLSTN

Send UNLISTEN command to serial bus.

Input: â€“

Output: â€“

Used registers: A.

Real address: $EDFE.

$FFB1 65457 LISTEN

Send LISTEN command to serial bus.

Input: A = Device number.

Output: â€“

Used registers: A.

Real address: $ED0C.

$FFB4 65460 TALK

Send TALK command to serial bus.

Input: A = Device number.

Output: â€“

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: â€“

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: â€“

Used registers: â€“

Real address: $FE00.

$FFBD 65469 SETNAM

Set file name parameters.

Input: A = File name length; X/Y = Pointer to file name.

Output: â€“

Used registers: â€“

Real address: $FDF9.

$FFC0 65472 OPEN

Open file. (Must call SETLFS and SETNAM beforehands.)

Input: â€“

Output: â€“

Used registers: A, X, Y.

Real address: ($031A), $F34A.

$FFC3 65475 CLOSE

Close file.

Input: A = Logical number.

Output: â€“

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: â€“

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: â€“

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: â€“

Output: â€“

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: â€“

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: â€“

Used registers: â€“

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: â€“

Used registers: â€“

Real address: $F6E4.

$FFDE 65502 RDTIM

Read Time of Day, at memory address $00A0-$00A2.

Input: â€“

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: â€“

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: â€“

Output: A = Byte read.

Used registers: A, X, Y.

Real address: ($032A), $F13E.

$FFE7 65511 CLALL

Clear file table; call CLRCHN.

Input: â€“

Output: â€“

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: â€“

Output: â€“

Used registers: A, X.

Real address: $F69B.

$FFED 65517 SCREEN

Fetch number of screen rows and columns.

Input: â€“

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: â€“

Output: X/Y = CIA #1 base address ($DC00).

Used registers: X, Y.

Real address: $E500.

$FFFA-$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.