Apple II Zero Page (by Andy McFadden; I don't remember the reference sources) LOCATION | USE DESCRIPTION -----------+----------------------------------------------------------------+ $00 - $02 | Jump instructions for Applesoft soft entry (ctrl-C) $03 - $05 | Jump instructions for Applesoft hard entry (ctrl-B) $06 - $09 | Used for sweet-16 registers $0A - $0C | Holds location for USR function's jump $0D - $1F | Temporary Applesoft/DOS 3.3 locations $20 | Left column of scroll window (def=$00) $21 | Width of scroll window (def=$28) $22 | Top line of scroll window (def=$00) $23 | Bottom line of scroll window (def=$18) $24 | Horizontal cursor displacement (from top) $25 | Vertical cursor position (abs) $26 - $27 | Hires byte position, lores left end point, DOS scratch $28 - $29 | Pointer to current text line $2A | Used as scratch during scrolling; DOS scratch $2B | Boot slot X 16 (after boot) $2C - $2F | RWTS storage for checksum, sector, track, volume $30 | Hires temporary bit mask; lores color value X 17 $31 | Used by monitor command processing $32 | Video format control: $FF=norm, $7F=flash, $3F=inverse $33 | Prompt character for input line $34 - $35 | Used by monitor command processing to save Y-reg $36 - $37 | Character output pointer $38 - $39 | Character input pointer $3A - $3B | Save area for program counter; set by L)ist and G)oto $3C - $3D | General use by monitor; source pointer for memory move $3E - $3F | General use by monitor $40 - $47 | General scratch for DOS $48 - $49 | RWTS IOB block pointer $4A - $4B | LOMEM address (INT) $4C - $4D | HIMEM address (INT) $4E - $4F | Random number field (seeded by RDKEY) $50 - $53 | 32-bit accumulator for use with Applesoft mult & divide $54 - $61 | Applesoft scratch locations $62 - $66 | Result of last multiply/divide $67 - $68 | Start of program address (Applesoft) $69 - $6A | Start of variable space address (Applesoft) $6B - $6C | Start of array space address (Applesoft) $6D - $6E | End of numeric storage address (Applesoft) $6F - $70 | Start of string storage address (Applesoft) $71 - $72 | Temporary pointer (string storage routines - Applesoft) $73 - $74 | HIMEM address (Applesoft) $75 - $76 | Line number being executed (Applesoft) $77 - $78 | Line where program stopped (Applesoft) $79 - $7A | Line being executed (Applesoft) $7B - $7C | Line where DATA is being read (Applesoft) $7D - $7E | Pointer to absolute memory location where DATA is (App) $7F - $80 | Pointer to source of input ($201 for INPUT statement) $81 - $82 | Last used variable name (Applesoft) $83 - $84 | Last used variable address $85 - $9C | General Applesoft usage $9D - $A3 | Main floating point accumulator $A4 | General use in Applesoft math routines $A5 - $AB | Secondary floating point accumulator $AC - $AE | General use Applesoft flags & pointers $AF - $B0 | Pointer to end of Applesoft program $B1 - $C8 | CHRGET routine: Applesoft calls whenever needs char $C9 | Applesoft scratch $CA - $CB | APRND random number; start of program address (INT) $CC - $CD | End of variable storage (INT) $CE - $CF | Math accumulator (INT) $D0 - $D5 | Applesoft hires scratch $D6 | Applesoft RUN flag (auto-run if >$80) $D7 | Scratch flag for Integer $D8 | Applesoft ONERR flag (active if >$80) $D9 | Used by DOS to test for Applesoft Def/Imm mode $DA - $DB | Line number where ONERR error occured $DC - $DD | TXTPTR save location for HNDLERR routine $DE | ONERR error code $DF | Applesoft stack pointer before error occured $E0 - $E1 | X-coordinate of last HPLOT $E2 | Y-coordinate of last HPLOT $E4 | HCOLOR value $E5 | Hires map byte for horizontal bit position $E6 | Hires plotting page $E7 | Scale value $E8 - $E9 | Start of shape table address $EA | Hires collision counter $EB - $EF | Totally, completely, unreasoningly unused $F0 | Applesoft lores scratch pointer $F1 | 256 minus SPEED value $F2 | Applesoft trace flag $F3 | FLASH mask ($40=flash, with $32 set to $7F) $F4 - $F8 | Applesoft ONERR pointers $F9 | Applesoft shape table ROT value $FA - $FE | Applesoft math temporary storage $FF | Unused (Integer scratch?) -----------+----------------------------------------------------------------+