APPENDIX TWO
A Graphics Memory Map
This diagram is not to scale; it is merely meant to give you a visual idea of the structure of the Atari memory. The numhers on the right are the memory pointers: these locations point to the addresses shown. The numhers on the left are the actual locations in memory. Location Contents Pointers +-------------------------------------------------------------+ 65535 _____ | Top of memory _____________________________________________ | | Operating System ROM | | | 60906-65535 | Device handler routines 794-831 HATABS | 59716-60905 | Serial Input/Output (SIO) utilities | 59093-59715 | Interrupt handler 512,513 VDSLST | | 514-527 Vectors | 58534-59092 | Central Input/Output (CIO) utilities | | | | | 58533 ____ | Operating System vectors __________________________________ | 58496-58533 | Initial RAM vectors on powerup | 58448-58495 | JMP vectors | 58432-58447 | Cassette | 58416-58431 | Printer | 58400-58415 | Keyboard | 58384-58399 | Screen | 58368-58383 | Editor | | | | | 58367 _____ | ROM Character set _________________ 756 CHBAS _____________ | | | | | 57344 | | | | | | 57343 _____ | Floating Point ROM package | | | | | 55295 _____ | I/O chips _________________________________________________ | | | | | 54784-55295 | Unused | 54272-54783 | ANTIC 756 CHBAS | | 755 CH1 | | 564-565 LPEN | | 560-561 SDLSTL | | 559 SDMCTL | 54016-54271 | PIA 636-639 PTRIG# | | 632-635 STICK# | 53760-54015 | POKEY 624-631 PADDL# | | 562 SSKCTL | | 16 POKMSK | 53504-53759 | unused | 53248-53503 | GTIA or CTIA 704-707 PCOLR# | | 708-712 COLOR# | | 644-647 STRIG# | | 623 GPRIOR | | | | | 53247 _____ | Unused 4K ROM block _______________________________________ | | | | | 49151 _____ | 8K BASIC ROM | | or Left cartridge (A) | | | | | 40959 _____ | Top of BASIC RAM or 106 RAMTOP | ____________|_____________________________________________________________| | 740 RAMSIZ | | | | Right cartridge (B) ROM if present | | (Atari 800 only) | | | | | Size and | | location | | vary with | | GRAPHICS | | mode | | | Text window screen RAM 60,661 TXTMSC | | 40800 for GR.0 | | | | Bottom of screen RAM 88,89 SAVMSC | | 40000 for GR.0 | | | | Display List: 560,561 SDLSTL | | 39968 for GR.0 | | | | Top of BASIC RAM 741,742 MEMTOP | (OS) | | | | | | | | 32768 | | | | | | 32767 _____ | User-program RAM __________________________________________ | | | | The amount of RAM can be ascertained by: | | PRINT FRE(0) | | | | Bottom varies: see note below | (13062) | Depends on buffer area allocated. | | | | | | RAM used by DOS and File System Manager | | | | 144,145 MEMTOP | | Stack for FOR-NEXT & GOSUB 142,143 RUNSTK | | 14,15 APPMHI | Size and | | location | | vary with | | program | | size | | | String & array table & | | end of BASIC program 140,141 STARP | | | | | | BASIC program | | area | | | | | | Statement table: 136,137 STMTAB | | Beginning of BASIC program | | Variable variable table 134,135 VVTP | | | | VNTP + 1 132,133 VNTD | | | | Variable name table 130,131 VNTP | | | (7420) | BASIC bottom of memory 743,744 MEMLO | | 128,129 LOMEM | | | | Sector buffers 4921,4937 SABUFL/H | 6781 | Drive & sector buffers 4905,4913 DBUFA1/H | 6047 | DOS vector 10,11 DOSVEC | 5440 | DUP.SYS start | | | 5377 | VTOC buffer | | DOS initialization 12,13 DOSINI | | or BASIC RAM without (743,744 MEMLO) | | DOS resident (128,129 LOMEM) | | FMSRAM | 1792 | DUP.SYS beginning | | | | | 1791 ______ | RAM used by OS and cartridge. | | (to bottom of RAM) | | | | Page six RAM | | | | +-------------------------------------------------+ | 1535 ____ | RAM used by BASIC _____________________________ | | | (to bottom of RAM) | | | | | 1406 | Floating Point RAM | | 1405 | BASIC RAM | | | | | | +-----------------------------------------+ | | 1151 | Operating System RAM | | | | | | | | | | | | Cassette buffer | | | | | | | | Printer buffer | | | | | | | | IOCB's | | | | | | | 512 | | | | | ______________________________________ | | | 511 | Stack | | | | | | | | | | | | | | | 256 | | | | | ______________________________________ | | | 255 | BASIC zero page RAM | | | | | | | | Floating Point pg. 0 | | | | | | | | Assembler Cart. pg. 0 | | | | | | | | | | | | | | | | | | | 128 | | | | | ______________________________________ | | | 127 | OS page zero RAM | | | | | | | | | | | | Zero page IOCB | | | | | | | | | | | 0 | Bottom of memory | +-----------+-------+-----------------------------------------+Notes
The bottom of the BASIC RAM depends on whether or not you have DOS files loaded in. Without DOS, LOMEM should be 1792, with DOS 7420. If you increase or decrease the number of disk and sector buffers by modifying DOS, this value will change again. See locations 743, 744 and 1801, 1802. The size and location of the variable, string and array tables depend on the program use and size. The more variables and arrays, the larger the memory the tables use. The size and address of the Display List and screen memory depend on the GRAPHICS mode in use. The first 256 bytes pointed to by LOMEM are the token output buffer. The actual BASIC program starts at the address pointed to by VNTP.
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