| 2000 | waitOnDraw | Cleared by alien-draw and set by next-alien. This ensures no alien gets missed while drawing. |
| 2001 | | |
| 2002 | alienIsExploding | Not-0 if an alien is exploding, 0 if not exploting |
| 2003 | expAlienTimer | Time (ISR ticks) left in alien-explosion |
| 2004 | alienRow | Row number of current alien (cursor) |
| 2005 | alienFrame | Animation frame number (0 or 1) for current alien (cursor) |
| 2006 | alienCurIndex | Alien cursor index (from 0 to 54) |
| 2007 | refAlienDYr | Reference alien delta Yr |
| 2008 | refAlienDXr | Reference alien deltaXr |
| 2009 | refAlienYr | Reference alien Yr coordinate |
| 200A | refAlienXr | Reference alien Xr coordinate |
| 200B | alienPosLSB | Alien cursor bit pos (LSB) |
| 200C | alienPosMSB | Alien cursor bit pos (MSB) |
| 200D | rackDirection | Value 0 if rack is moving right or 1 if rack is moving left |
| 200E | rackDownDelta | Constant value of alien rack dropping after bumping screen edge |
| 200F | | |
| 2010 | obj0TimerMSB | |
| 2011 | obj0TimerLSB | Wait 128 interrupts (about 2 secs) before player task starts |
| 2013 | obj0HanlderLSB | |
| 2014 | oBJ0HanlderMSB | Player handler code at 028E |
| 2015 | playerAlive | Player is alive (FF=alive). Toggles between 0 and 1 for blow-up images. |
| 2016 | expAnimateTimer | Time till next blow-up sprite change (reloaded to 5) |
| 2017 | expAnimateCnt | Number of changes left in blow-up sequence |
| 2018 | plyrSprPicL | Player sprite descriptor ... picture LSB |
| 2019 | plyrSprPicM | Player sprite descriptor ... picture MSB |
| 201A | playerYr | Player sprite descriptor ... location LSB |
| 201B | playerXr | Player sprite descriptor ... location MSB |
| 201C | plyrSprSiz | Player sprite descriptor ... size of sprite |
| 201D | nextDemoCmd | Next movement command for demo |
| 201E | hidMessSeq | Set to 1 after 1st of 2 sequences are entered for hidden-message display |
| 201F | | Appears to be unused |
| 2020 | obj1TimerMSB | |
| 2021 | obj1TimerLSB | |
| 2023 | obj1HandlerLSB | |
| 2024 | obj1HandlerMSB | Shot handler code at 03BB |
| 2025 | plyrShotStatus | 0 if available, 1 if just initiated, 2 moving normally, 3 hit something besides alien, 5 if alien explosion is in progress, 4 if alien has exploded (remove from active duty) |
| 2026 | blowUpTimer | Sprite blow-up timer |
| 2027 | obj1ImageLSB | |
| 2028 | obj1ImageMSB | Sprite image at 1C90 (just one byte) |
| 2029 | obj1CoorYr | Player shot Y coordinate |
| 202A | obj1CoorXr | Player shot X coordinate |
| 202B | obj1ImageSize | Size of shot image (just one byte) |
| 202C | shotDeltaX | Shot's delta X |
| 202D | fireBounce | 1 if button has been handled but remains down |
| 202E | | |
| 202F | | |
| 2030 | obj2TimerMSB | |
| 2031 | obj2TimerLSB | |
| 2033 | obj2HandlerLSB | |
| 2034 | obj2HandlerMSB | Handler code at 0476 |
| 2035 | rolShotStatus | |
| 2036 | rolShotStepCnt | |
| 2037 | rolShotTrack | A 0 means this shot tracks the player |
| 2038 | rolShotCFirLSB | Pointer to column-firing table LSB (not used for targeting) |
| 2039 | rolShotCFirMSB | Pointer to column-firing table MSB (not used for MSB counter |
| 203A | rolShotBlowCnt | |
| 203B | rolShotImageLSB | |
| 203C | rolShotImageMSB | |
| 203D | rolShotYr | |
| 203E | rolShotXr | |
| 203F | rolShotSize | |
| 2040 | obj3TimerMSB | |
| 2041 | obj3TimerLSB | |
| 2043 | obj3HandlerLSB | |
| 2044 | obj3HandlerMSB | Handler code at 04B6 |
| 2045 | pluShotStatus | |
| 2046 | pluShotStepCnt | |
| 2047 | pluShotTrack | A 1 means this shot does not track the player |
| 2048 | pluShotCFirLSB | Pointer to column-firing table LSB |
| 2049 | pluShotCFirMSB | Pointer to column-firing table MSB |
| 204A | pluShotBlowCnt | |
| 204B | pluShotImageLSB | |
| 204C | pluShotImageMSB | |
| 204D | pluShotYr | |
| 204E | pluSHotXr | |
| 204F | pluShotSize | |
| 2050 | obj4TimerMSB | |
| 2051 | obj4TimerLSB | |
| 2053 | obj4HandlerLSB | |
| 2054 | obj4HandlerMSB | Handler code at 0682 |
| 2055 | squShotStatus | |
| 2056 | squShotStepCnt | |
| 2057 | squShotTrack | A 1 means this shot does not track the player |
| 2058 | squShotCFirLSB | Pointer to column-firing table LSB |
| 2059 | squShotCFirMSB | Pointer to column-firing table MSB |
| 205A | squSHotBlowCnt | |
| 205B | squShotImageLSB | |
| 205C | squShotImageMSB | |
| 205D | squShotYr | |
| 205E | squShotXr | |
| 205F | squShotSize | |
| 2060 | endOfTasks | FF marks the end of the tasks list |
| 2061 | collision | Set to 1 if sprite-draw detects collision |
| 2062 | expAlienLSB | |
| 2063 | expAlienMSB | Exploding alien picture 1CC0 |
| 2064 | expAlienYr | Y coordinate of exploding alien |
| 2065 | expAlienXr | X coordinate of exploding alien |
| 2066 | expAlienSize | Size of exploding alien sprite (16 bytes) |
| 2067 | playerDataMSB | Current player's data-pointer MSB (21xx or 22xx) |
| 2068 | playerOK | 1 means OK, 0 means blowing up |
| 2069 | enableAlienFire | 1 means aliens can fire, 0 means not |
| 206A | alienFireDelay | Count down till aliens can fire (2069 flag is then set) |
| 206B | oneAlien | 1 when only one alien is on screen |
| 206C | temp206C | Holds the value ten ... number of characters in each "=xx POINTS" string but gets set to 18 in mem copy before game. |
| 206D | invaded | Set to 1 when player blows up because rack has reached bottom |
| 206E | skipPlunger | When there is only one alien left this goes to 1 to disable the plunger-shot when it ends |
| 206F | | |
| 2070 | otherShot1 | When processing a shot, this holds one of the other shot's info |
| 2071 | otherShot2 | When processing a shot, this holds one of the other shot's info |
| 2072 | vblankStatus | 80=screen is being drawn (don't touch), 0=blanking in progress (ok to change) |
| 2073 | aShotStatus | Bit 0 set if shot is blowing up, bit 7 set if active |
| 2074 | aShotStepCnt | Count of steps made by shot (used for fire reload rate) |
| 2075 | aShotTrack | 0 if shot tracks player or 1 if it uses the column-fire table |
| 2076 | aShotCFirLSB | Pointer to column-firing table LSB |
| 2077 | aShotCFirMSB | Pointer to column-firing table MSB |
| 2078 | aShotBlowCnt | Alen shot blow up counter. At 3 the explosion is drawn. At 0 it is done. |
| 2079 | aShotImageLSB | Alien shot image LSB |
| 207A | aShotImageMSB | Alien shot image MSB |
| 207B | alienShotYr | Alien shot delta Y |
| 207C | alienShotXr | Alien shot delta X |
| 207D | alienShotSize | Alien shot size |
| 207E | alienShotDelta | Alien shot speed. Normally -1 but set to -4 with less than 9 aliens |
| 207F | shotPicEnd | the last picture in the current alien shot animation |
| 2080 | shotSync | All 3 shots are synchronized to the GO-2 timer. This is copied from timer in the game loop |
| 2081 | tmp2081 | Used to hold the remember/restore flag in shield-copy routine |
| 2082 | numAliens | Number of aliens on screen |
| 2083 | saucerStart | Flag to start saucer (set to 1 when 2091:2092 counts down to 0) |
| 2084 | saucerActive | Saucer is on screen (1 means yes) |
| 2085 | saucerHit | Saucer has been hit (1 means draw it but don't move it) |
| 2086 | saucerHitTime | Hit-sequence timer (explosion drawn at 1F, score drawn at 18) |
| 2087 | saucerPriLocLSB | Mystery ship print descriptor ... coordinate LSB |
| 2088 | saucerPriLocMSB | Mystery ship print descriptor ... coordinate MSB |
| 2089 | saucerPriPicLSB | Mystery ship print descriptor ... message LSB |
| 208A | saucerPriPicMSB | Mystery ship print descriptor ... message MSB |
| 208B | saucerPriSize | Mystery ship print descriptor ... number of characters |
| 208C | saucerDeltaY | Mystery ship delta Y |
| 208D | sauScoreLSB | Pointer into mystery-ship score table (MSB) |
| 208E | sauScoreMSB | Pointer into mystery-ship score table (LSB) |
| 208F | shotCountLSB | Bumped every shot-removal. Saucer's direction is bit 0. (0=2/29, 1=-2/E0) |
| 2090 | shotCountMSB | Read as two-bytes with 208F, but never used as such. |
| 2091 | tillSaucerLSB | |
| 2092 | tillSaucerMSB | Count down every game loop. When it reaches 0 saucer is triggerd. Reset to 600. |
| 2093 | waitStartLoop | 1=in wait-for-start loop, 0=in splash screens |
| 2094 | soundPort3 | Current status of sound port (out $03) |
| 2095 | changeFleetSnd | Set to 1 in ISR if time to change the fleet sound |
| 2096 | fleetSndCnt | Delay until next fleet movement tone |
| 2097 | fleetSndReload | Reload value for fleet sound counter |
| 2098 | soundPort5 | Current status of sound port (out $05) |
| 209A | tilt | 1 if tilt handling is in progress |
| 209B | fleetSndHold | Time to hold fleet-sound at each change |
| 209C | | |
| 209D | | |
| 209E | | |
| 209F | | |
| 20A0 | | |
| 20A1 | | |
| 20A2 | | |
| 20A3 | | |
| 20A4 | | |
| 20A5 | | |
| 20A6 | | |
| 20A7 | | |
| 20A8 | | |
| 20A9 | | |
| 20AA | | |
| 20AB | | |
| 20AC | | |
| 20AD | | |
| 20AE | | |
| 20AF | | |
| 20B0 | | |
| 20B1 | | |
| 20B2 | | |
| 20B3 | | |
| 20B4 | | |
| 20B5 | | |
| 20B6 | | |
| 20B7 | | |
| 20B8 | | |
| 20B9 | | |
| 20BA | | |
| 20BB | | |
| 20BC | | |
| 20BD | | |
| 20BE | | |
| 20BF | | |
| 20C0 | isrDelay | Delay counter decremented in ISR |
| 20C1 | isrSplashTask | 1=In demo, 2=Little-alien and Y, 4=shooting extra 'C' |
| 20C2 | splashAnForm | Image form (increments each draw) |
| 20C3 | splashDeltaX | Delta X |
| 20C4 | splashDeltaY | Delta Y |
| 20C5 | splashYr | Y coordinate |
| 20C6 | splashXr | X coordinate |
| 20C7 | splashImageLSB | |
| 20C8 | splashImageMSB | Base image 1BA0 (small alien with upside down Y) |
| 20C9 | splashImageSize | Size of image (16 bytes) |
| 20CA | splashTargetY | Target Y coordinate |
| 20CB | splashReached | Reached target Y flag (1 when reached) |
| 20CC | splashImRestLSB | Base image for restore 1BA0 is small alien with upside down Y |
| 20CD | splashImRestMSB | |
| 20CE | twoPlayers | 1 for yes, 0 means 1 player |
| 20CF | aShotReloadRate | Based on the MSB of the player's score ... how fast the aliens reload their shots |
| 20D0 | | ; This is where the alien-sprite-carying-the-Y ... |
| 20D1 | | ; ... lives in ROM |
| 20D2 | | |
| 20D3 | | |
| 20D4 | | |
| 20D5 | | |
| 20D6 | | |
| 20D7 | | |
| 20D8 | | |
| 20D9 | | |
| 20DA | | |
| 20DB | | |
| 20DC | | |
| 20DD | | |
| 20DE | | |
| 20DF | | |
| 20E0 | | |
| 20E1 | | |
| 20E2 | | |
| 20E3 | | |
| 20E4 | | |
| 20E5 | player1Ex | Extra ship has been awarded = 0 |
| 20E6 | player2Ex | Extra ship has been awarded = 0 |
| 20E7 | player1Alive | 1 if player is alive, 0 if dead (after last man) |
| 20E8 | player2Alive | 1 if player is alive, 0 if dead (after last man) |
| 20E9 | suspendPlay | 1=game things are moving, 0=game things are suspended |
| 20EA | coinSwitch | 1=switch down, 0=switch up (used to debounce coin switch) |
| 20EB | numCoins | number of coin credits in BCD format (99 max) |
| 20EC | splashAnimate | 0 for animation during splash and 1 for not. This alternates after every cycle. |
| 20ED | demoCmdPtrLSB | pointer to demo commands LSB 1663 |
| 20EE | demoCmdPtrMSB | pointer to demo commands MSB |
| 20EF | gameMode | 1=game running, 0=demo or splash screens |
| 20F0 | | |
| 20F1 | adjustScore | Set to 1 if score needs adjusting |
| 20F2 | scoreDeltaLSB | Score adjustment (LSB) |
| 20F3 | scoreDeltaMSB | Score adjustment (MSB) |
| 20F4 | HiScorL | Hi-score descriptor ... value LSB |
| 20F5 | HiScorM | Hi-score descriptor ... value MSB |
| 20F6 | HiScorLoL | Hi-score descriptor ... location LSB |
| 20F7 | HiScorLoM | Hi-score descriptor ... location MSB |
| 20F8 | P1ScorL | Hi-score descriptor ... value LSB |
| 20F9 | P1ScorM | Hi-score descriptor ... value MSB |
| 20FA | P1ScorLoL | Hi-score descriptor ... location LSB |
| 20FB | P1ScorLoM | Hi-score descriptor ... location MSB |
| 20FC | P2ScorL | Hi-score descriptor ... value LSB |
| 20FD | P2ScorM | Hi-score descriptor ... value MSB |
| 20FE | P2ScorLoL | Hi-score descriptor ... location LSB |
| 20FF | P2ScorLoM | Hi-score descriptor ... location MSB |
