A.N.A.L.O.G. ISSUE 24 / NOVEMBER 1984 / PAGE 72

Race in Space

16K Cassette or 24K Disk

by Charles Bachand

This month’s assembly language game, Race in Space, is a two-player game with options that allow 128 different variations.

You and a friend (or enemy) must race your spaceships through a densely-packed asteroid field if your ship makes contact with any other object, it will be damaged and must return to its launch point. Race in Space is a semi-violent game where no one gets killed.

Typing it in.

Before typing anything, look at the listings accompanying this article.

Listing 1 is the BASIC data and data checking routine. This listing is used to create both cassette and disk versions of Race in Space. The data statements are listed in hexadecimal (base 16), so the program will fit in 16K cassette system.

Listing 2 is the assembly language source code for the game of Race in Space, created with the OSS MAC/65 assembler. You don’t have to type this listing to play the game! It is included for those readers interested in assembly language.

Follow the instructions below to make either a cassette or disk version of Race in Space.

Cassette instructions.

1. Type Listing 1 into your computer using the BASIC cartridge and verify your typing with Unicheck (see page 90).

2. Type RUN and press RETURN. The program will begin and ask:


Type 0 and press RETURN. The program will begin checking the DATA statements, printing the line number of each as it goes. It will alert you if it finds any problems. Fix any incorrect lines and re-RUN the program, if necessary, until all errors are eliminated.

3. When all of your DATA lines are correct, the computer will beep twice and prompt you to READY CASSETTE AND PRESS RETURN. Now, insert a blank cassette in your recorder, press the RECORD and PLAY buttons simultaneously and hit RETURN. The message WRITING FILE will appear, and the program will create a machine language boot tape version of Race in Space, printing each DATA line number as it goes. When the READY prompt appears, the game is recorded and ready to play. CSAVE the BASIC program onto a separate tape before continuing.

4. To play the game, rewind the tape created by the BASIC program to the beginning. Turn your computer OFF and remove all cartridges. Press the PLAY button on your recorder and turn ON your computer while holding down your START key. If you have a 600 or 800XL computer, you must hold the START and OPTION keys when you turn on the power. The computer will “beep” once. Hit the RETURN key, and Race in Space will load and run automatically.

Disk instructions.

1. Type Listing 1 into your computer, using the BASIC cartridge and verify your typing with Unicheck (see page 90).

2. Type RUN and press RETURN. The program will ask:


Type 1 and press RETURN. The program will begin checking the DATA lines, printing the line number of each statement as it goes. It will alert you if it finds any problems. Fix incorrect lines and re-RUN the program, if necessary, until ali errors are eliminated.

3. When all DATA lines are correct, you will be prompted to INSERT DISK WITH DOS, PRESS RETURN. Put a disk containing DOS 2.0S into drive #1 and press RETURN. The message WRITING FILE will appear, and the program will create an AUTORUN.SYS file on the disk, displaying each DATA line number as it goes. When the READY prompt appears, the game is ready to play. Be sure the BASIC program is SAVEd before continuing.

4. To play the game, insert the disk containing the AUTORUN.SYS file into drive #1. Turn your computer OFF, remove all cartridges and turn the computer back ON. Race in Space will load and run automatically.

Playing the game.

Race in Space requires the use of two joysticks plugged into ports 1 and 2. When the game starts, you are presented with a scrolling title screen. Td enter the game options screen from either the intro screen or the game play screen, simply press OPTION.

When in the options menu, use the OPTION key to select which option to change, and then use the SELECT key to change it. Use the START key to begin game play. While in the options menu, you may also press one of the number keys from I to 9 to change the time limit for the game from the default of three minutes. All selected options will remain in effect for subsequent game plays.

Game options.

Race in Space has five options that can be changed within the options menu to suit your own personal tastes. These options have been broken down for you here:

1. Trigger — NO EFFECT renders the trigger button completely useless.

SHIELDS will put up a protective barrier around your ship that will allow objects to pass through it without harm. Unfortunately, all the power from your engines will be used to run the shields, thus leaving you dead in space.

MISSILES allow both you and your opponent to fight it out in outer space using mega-menace Boomerang missiles, which automatically lock onto your enemy’s coordinates when fired. To save yourself, you must move your ship out of the path of the oncoming missile. Only one missile per ship is allowed on the screen at any one time. You may fire a missile when the top of your ship has a “knob” on it (this is your missile). Every time your missile hits your opponent’s ship, or is absorbed by a comet (see COMETS), you will receive one point.

WARP DRIVE allows your ship to travel at twice its normal cruising speed, using its wave-motion engine. At this speed, you must be twice as careful.

2. Density — This varies the number of asteroids present on the game screen. Choosing from STANDARD, DOUBLE, TRIPLE or SUPER will increase the number of asteroids, thereby increasing their density on the playfield and the game difficulty.

3. Comets — Comets can either be ENABLED or DISABLED and roar across the screen at random intervals. You can hear a comet as it approaches, and as it travels across the screen.

4. Universe — You will normally fly through a POSITIVE universe, one that is very stable. This is the default setting and the one that you will, most likely, use. Adventurous people can explore the dangers of a NEGATIVE universe, where space itself will flash at random intervals.

Every time your ship reaches the top of the screen, a new one will reappear at the bottom — at your launch site — and you will be awarded one point. The winner is simply the player with the most points at the end of the game. Race in Space will end when either player reaches 99 points, or you run out of time. Good luck; you’ll need it!

Listing 1.
BASIC listing.

10 REM *** RACE IN SPACE ***
30 TRAP 40000:DATA 0,1,2,3,4,5,6,7,8,9,0,0,0,0,0,0,0,10,11,12,13,14,15
70 FOR X=1 TO 89 STEP 2:D1=ASC(DAT$(X,X))-48:D2=ASC(DAT$(X+1,X+1))-48:BYTE=HEX(D1)*16+HEX(D2)
110 GOTO 220
120 IF PEEK(195)<>6 THEN 220
130 IF PASS=0 THEN 170
140 IF  NOT DSK THEN 160
150 PUT #1,224:PUT #1,2:PUT #1,225:PUT #1,2:PUT #1,187:PUT #1,47:CLOSE #1:END 
160 FOR X=1 TO 89:PUT #1,0:NEXT X:CLOSE #1:END 
170 IF  NOT DSK THEN 200
190 PUT #1,255:PUT #1,255:PUT #1,0:PUT #1,32:PUT #1,254:PUT #1,47:GOTO 210
210 ? :? "WRITING FILE":PASS=2:LINE=990:RESTORE 1000:TRAP 120:GOTO 50
230 DATA 0,33,216,31,255,31,169,0,141,47,2,169,60,141,2,211,169,0,141,231,2,133,14,169,56,141,232,2
240 DATA 133,15,169,187,133,10,169,47,133,11,24,96
1000 DATA 0000000000000000000000007B3232320000000060A0A020007E42427E424200007E404040407E00007C464646,79
1010 DATA 467C00007E407C40407E00007E407C40404000007E40404E427E000042427E42424200007E181818187E000040,739
1020 DATA 404040407E00007E424242424200007E42427E404000007E42427E4C4600007E181818181800004242425A5A7E,369
1030 DATA 000042427E181818007E81BDA1A1BD817E007E424242427E000008080808080800007E027E40407E00007E027E,235
1040 DATA 02027E000042427E02020200007E407E02027E00007E407E42427E00007E020202020200007E427E42427E0000,361
1050 DATA 7E427E02027E00000000000000000018245A00000000000000183C3C1800000000003C7E7E7E3C000000007EFF,6
1060 DATA FFFF00000000003C7E7E000000000000183C000000000000001800000000000000000000000000000000000000,936
1070 DATA 00000000003C00000000000000FFFFFF7E000000007E7E3C00000000003C180000000000001800000000000000,307
1080 DATA 00181818183C7E5A1818183C7EFFDB0000000000000000000042424242427E0000001818001818000042424242,227
1090 DATA 241800007E5A5A4242420000464C78584C4600FFFFFFFFFFFFFFFF7E42420042427E0002020200020202003E02,923
1100 DATA 023C40407C003E02023C02023E004242423C020202007C40403C02023E007C40403C42427E003E020200020202,713
1110 DATA 007E42423C42427E007E42423C02023E00706700202727272727272727272727272707C1001270707046911307,222
1120 DATA 462F1446B0130606462F1446DF13463E14462F1446EF13467A14462F1446FF1346B614462F14460F1446D41446,281
1130 DATA 2F14461F1446F214462F144691134115127070704F0020000F000F000F000F000F000F000F000F000F000F000F,888
1140 DATA 000F000F000F000F000F000F000F000F000F000F000F000F000F000F000F000F000F000F000F000F000F000F00,218
1150 DATA 0F000F000F000F000F000F000F000F000F000F000F000F000F000F000F000F000F000F000F000F000F000F000F,563
1160 DATA 000F000F000F000F000F000F000F000F000F000F000F000F000F000F000F000F000F000F000F7030C700083042,329
1170 DATA 1115415A12187E7EFFFF7E7E18000000555500000015030C030B1308FF2433030803150A0C06FF444D4E465846,960
1180 DATA 4C4F58FF618E838486808A8C80988D8384860102FF83504E4A4F4F464C405B51FFA0C4C9C3CECBC6D8C0C0DBC3,107
1190 DATA C4C9C3CCC5FFC51200141C1B17FFE6AD8080ADFFF66E40406EFF000000000000000000CDCEC6D8D8C0D3CDCFCA,917
1200 DATA D3CCC0C0000000000000000000757575757575757575757575757575757500130D0F0A130C18C0C0CFF1968075,44
1210 DATA 00534D4F4A534C71408B86878F8075750058464B46444F71CECAC8C9CFC0757500584F434E4F7100000D0B0311,159
1220 DATA 0075000F0E0A0808060E31000000000075750085868C988A8F91B1808000000075750098898A8D98B100000000,183
1230 DATA 0000007575008493B3868F98B1000000000000757500B08C8AB2868E9886B10000000075750000000000000000,320
1240 DATA 0000000000007500000000CCD3C0C6C7C7C6C4CFC075000000000000D8C9CAC6CBC5D8C0750000000000F3CAD8,953
1250 DATA D8CACBC6D8C075000000D0C3CECDC0C5CECAF2C6C0750000000000D8CFC3CCC5C3CEC5C07500000000000000C5,780
1260 DATA D3F0DBCBC6C07500000000000000CFCECACDCBC6C0750000000000000000D8F0CDC6CEC075000000000000CED3,481
1270 DATA C4F4C6CFD8C075000000000000D8C3F0C4C6CED8C0750000000000C5CAD8C3DBCBC6C5C075000000000000C6CC,965
1280 DATA C3DBCBC6C5C0750000000000CDD3D8CACFCAF2C6C0750000000000CCC6C8C3CFCAF2C600750000000004130D11,94
1290 DATA 0E0A08090F001200030C030B13080033030803150A0C0600141C1B170000000000001313000000F9F1F6F6E4F6,930
1300 DATA 0000001313000003000000001F1E1A181D1B333530FCF303000301010101030003020302020302000000000E0D,842
1310 DATA 34123D1246124F122B123E144D145C146B147A1489149814A714B614C514D414E314F214011503030101010004,508
1320 DATA 04020200183C3C185A7E5A4200187EDB7E0000000000B66DDBB61020010258A003115030C434003C7E7EFFFFFF,15
1330 DATA FFFFFF7E7E3C00C646F666266CA251404848E683A5140A29CE8DC2026840AD1FD0A8458225828482C904608D02,265
1340 DATA D2A9A48D03D2A0C0CAD0FD864D88D0F88C03D260A200A9A48D01D28D03D2A912C583D0FC20EB15D00568684CA4,554
1350 DATA 17A9008583E88A8D03D029FC8D02D04A4A4AA8B971139939218A0A0A0A0A0A49F08D00D21869028D02D28AD0C4,204
1360 DATA 8D03D2858560A207A9009D00D0CA10FA60A9008D01D28D03D28D05D28D07D260A93C8D02D3A92B8580A9128581,377
1370 DATA A9008D08D2A2559582CA10FBA9298D2F02A9038D0FD2A9398D07D4A9028D1DD0A9DE8D0002A9158D0102A9C08D,343
1380 DATA 0ED4A9108DF402A9C68DC502A9948DC602A9048DC302A9018D0AD08D0BD08D6F02205A1685A18586206516AA9D,347
1390 DATA 00209D00219D00229D003BCAD0F1A207BD0A139D283BBD02139DA83BCA10F1E8BD1213F010A8E8BD1213C9FFF0,359
1400 DATA F1990021C84C0117A9008D3002A9128D3102A9208D0312A9008D0212854D8585A9102483F0FC20EB15D0034CA4,577
1410 DATA 17A9008583E684A584186D021245868D00D2A584290769DD8D06228D092269088D16228D1922A584C910D03BA9,895
1420 DATA 0085848D05D4E685A586458509808D01D2AD02121869108D0212901EEE0312A922CD0312D0034C8D16200E16A9,919
1430 DATA 208D00D2A98F8D01D2A90F8586A5848D05D44C2817A583C583F0FCA9218D2F02A9158D3002A9128D310220281F,582
1440 DATA 205A16854D8D1DD020651685A085A1A9948DC602A9048592A692BDD4158DC502BDD91520F815C69210EEADFC02,993
1450 DATA 293FA209DD5115F005CAD0F8F01D8A8D4D151869938DAE138A69F68D4015A9FF8DFC028A0A0A493F20F81520EB,146
1460 DATA 154A90034CA01D4A9024A93020F815A687F689B5893D99159589058E0AAAA000BD7D159180C8BD7E1591804CE6,158
1470 DATA 174A909FA91020F815A2018688A5870A0A0A0AAAA00DA9805DE0139DE013E88810F4A588D0034CE617E687A587,327
1480 DATA 0AAABD71158580BD72158581A687BD9E15658E858EA200A587C905D0C18687868E4C4E18A9008593A8A92C8594,767
1490 DATA A906859160A902858FEC0AD22690069006900690C68FD0F1A5909193602094180691A68A20A218C8D0FAE694C6,449
1500 DATA 91D0F4C694A906859188B1934A919398D0F7C694C691D0F160A00A99000A99800A8810F7BDBE1595D49D00D08A,799
1510 DATA 48BDC015AAFE0008BD0008C91D9008A9139D0008FEFF0768AABDC2158D04D2A9AE8D05D2A90385B5D6AED004A9,140
1520 DATA 0085ADA9FF8D1ED0608A48A5836AB02EC6B41004A90285B4A6B4BDB6158DAF15293C8DA515BDB715293C8DA615,386
1530 DATA A583290EAABD5D158D6E15BD5E158D6F1568AA60CE1808105BA9058D1808A5B5F005C6B54C7B198D05D2CE0C08,897
1540 DATA CE17081042A9FF8D0C08A9098D1708A5B5D00AA9A48D05D2A9408D04D2CE0A08CE16081022A9FF8D0A08A9098D,404
1550 DATA 1608CE0908CE15081010A9FB8D0908A9058D1508CE0708CE140808A5B505CB05CCD01BA5A825A9F015A5B705B8,644
1560 DATA F00FA9288D05D2A5834A290709088D04D22860AD09D02901D010AD04D029040D0CD0F00AA5B0C901F004A90085,48
1570 DATA A8AD08D02902D010AD05D029040D0DD0F00AA5B1C901F004A90085A960B5B7D0FBB5B0C902F00395B260D5B2F0,822
1580 DATA EE95B295B718B5D4690285CF95C7B5D685D0E6D095BFF6BF8AF00BA5D4690285CDA5D64C601AA5D5690285CDA5,658
1590 DATA D785CEE6CEA90195C195C938A5CEE5D095BBB00AA9FF95C155BB95BBF6BB38A5CDE5CF95C5B00AA9FF95C955C5,153
1600 DATA 95C5F6C5A90095C395B9B5C595BDA90F95CBB5BBD5BD900695BD4A95C360B5BD4A95B9604820EB19202D19E683,514
1610 DATA 18A5AC693085AC8D02D2A5ADD0034C611CA9088D17D08A48A20FA5A8D0038E7802A5A9D0038E7902AD78022D79,451
1620 DATA 02C90FA981B00CA5B005B1C903A988B002A9848D07D2A918B002A9208D06D2A20086B6E8AD08D085D2AD09D085,918
1630 DATA D3A5B005B1C901D00FAD0AD2291F09208D06D2A9A68D07D220E11CB5A8F034B5B0C901F02E20221AA5836A9006,48
1640 DATA B5B0C903D0205E7802B002D6D65E7802B002F6D6A58BF00E5E7802B002D6D45E7802B002F6D4B5D4C930B002A9,744
1650 DATA 30C9C89002A9C795D49D00D08492B5A83024A5836AB01D0A29F69DC002A5B5D013A583290709C88D05D2AD0AD2,274
1660 DATA 291F09208D04D2F6D6B5D6D00320E318C9C0902BB5A8D025B5D4DDBE15F00AF6D4901AD6D4D6D4D014A9FF95A8,789
1670 DATA 8D1ED0BDC4159DC002A5B5D0038D05D2A9BF95D6E0016A859B9007A5B61DBA1585B68A4818B5A8F019AD0AD229,511
1680 DATA 0F1DC4159DC002B5B0C90138F00718BDC4159DC002A009A209A58BF002A212BDA31590032D0AD2919BCA8810F2,513
1690 DATA 68AAB5B7F006A001A900919BA492CA30034C2B1BA5B68D1CD0A5ADF013206519101CA9F68D07088D09088D0A08,147
1700 DATA 8D0C08A979854DA90085AD8D05D28D07D268AAA5A42583F0026840A5AAF0FA98488A48A5A225A7D009A5A51865,640
1710 DATA A6297F85A5A00DA6A5AD0AD239C6159D000BAD0AD239C6159D800BE88A297FAA8810E6AD0AD229F009048DC202,692
1720 DATA AD0AD229F009088DC30218A5A265A385A28D02D08D03D085AAE6ABA5ADF011A5ABC97DB00E4A4A8D00D2C91890,353
1730 DATA 05499F8D01D268AA68A86840BD84024AB002A58935A8D5B0F0038D1ED095B0B5B7F006B5BFD00395B76018B5BB,103
1740 DATA 75B995B9D5BD900BF5BD95B918B5C175BF95BF18B5C575C395C3D5BD900BF5BD95C318B5C975C795C7B5CBF012,215
1750 DATA 4A09888D05D2B5CB490F0A0A0A8D04D2D6CBB5C79D04D0B5BF4A900948A5B61DBC1585B6680980859DB5D23D71,480
1760 DATA 15D022B5C7F01E9848A003B19D3D5B1585D1B96D15E001D0020A0A05D1919D8810E968A860A90095B79848A003,556
1770 DATA B19D3D5B15919D8810F6B5D23D7115F00320F61868A8602065168D1ED0A9FF85A885A9A9408D0ED4A90C8591A9,51
1780 DATA 008593A9208594A909859EA9218D6F028D06D2A9018D0AD08D0BD085ADA96385AE85AFA218BD39159D0008CA10,9
1790 DATA F7A90A859C20281FA9058D0CD0A90085A285A085AA854D85B585B785B8A89193C8D0FBE694C691D0F5A9BF85D6,579
1800 DATA 85D79899800999000A99000BC8D0F420BA18A201BDBE159D00D095D4CA10F5E88EC6028690A92E8D2F028DC502,939
1810 DATA A9088D07D4A9038D1DD0A9C48DC002A9348DC102A9B08D0002A91A8D0102A95A8D3002A9128D3102A9C08D0ED4,667
1820 DATA 20941866909007B1930980189002B1936A9193C8D0F8E694C691D0F2A9068591A9008593A937859488B1932A91,502
1830 DATA 9398D0F7C694C691D0F12690859585978593A9328596A92C8598A9208594A9EC8599A91F859AA24CA013B19511,842
1840 DATA 97919391998810F5A595186914859585979004E696E69818A593692885939002E69418A599692885999002E69A,507
1850 DATA CAD0CB20EB1590034CA4176A90034CA01DA58DF04EA5A0F033202D1FC69FA5ADF005A59F4A09A08D03D2A59FF0,109
1860 DATA 300A0A0A49FF85ACD02CA5A16A900FA204A90F5DC4029DC402CA10F5C6A160AD0AD2293FD010202D1FA91F859F,898
1870 DATA 85A0D00585A08D03D2A58CF004A5AAF0034C6A1EAD0AD2293FD0F685A4AA9D000BCAD0FA8D02D08D03D085ABAD,816
1880 DATA 0AD22903C903B0F785A6C6A6AD0AD22903AAA91F4ACA10FC85A7A5ADF002A9888D01D2AD0AD2293F691085A5A2,336
1890 DATA FE86AAAD0AD21002A20286A3AD0AD210A6E6A44C6A1EA9208596A9108598AAA90085958597A8B195919788D0F9,189
1900 DATA E696E698CAD0F24C74160000000000000000000000000000000000000000000000000000000000000000000000,817

(see page 90)

10 DATA 551,351,496,811,423,729,200,603,555,573,694,613,29,205,227,7060
160 DATA 773,198,962,638,491,30,155,105,309,55,181,206,334,77,966,5480
1060 DATA 760,927,68,666,80,109,432,216,301,300,274,480,171,97,546,5427
1210 DATA 698,173,54,544,895,622,754,16,149,907,268,802,994,991,727,8594
1360 DATA 966,902,865,957,640,603,511,762,944,24,809,859,907,684,806,11239
1510 DATA 46,984,937,909,847,4,921,240,546,122,58,873,948,912,843,9190
1660 DATA 104,69,785,912,950,11,983,913,244,72,771,121,924,234,9,7102
1810 DATA 946,608,910,613,58,50,961,29,909,773,5857

Listing 2.
BASIC listing.

;   +---------------+
;   +---------------+
; Written by Charles Bachand
ORIGIN	=	$1000
; Game Playfield Area
; -------------------
MRAM	=	DRAM+$1900
; Player/Missile Area
; -------------------
	*=	$0800
PM	*=	*+$0180	;blank space
PMM	*=	*+$80	;missiles
PM0	*=	*+$80	;player 0
PM1	*=	*+$80	;player 1
PM2	*=	*+$80	;player 2
PM3	*=	*+$80	;player 3
; System Equates
; --------------
TRAM	=	PM	;PM blank space
CHBAS	=	$02F4	;char base reg
CH	=	$02FC	;last key press
VSCROL	=	$D405	;vertical scroll
NMIEN	=	$D40E	;interrupt ctrl
VDSLST	=	$0200	;DLI vector
SDMCTL	=	$022F	;DMA enable
SDLSTL	=	$0230	;display list
COLOR0	=	$02C4	;color reg 0
COLOR1	=	$02C5	;color reg 1
COLOR2	=	$02C6	;color reg 2
COLPF1	=	$D017	;color playfld 1
DLI	=	$80	;DLI flag
ATRACT	=	77	;attract mode
RTCLOK	=	20	;real time clock
PCOLR0	=	$02C0	;player color 0
PCOLR1	=	$02C1	;player color 1
PCOLR2	=	$02C2	;player color 2
PCOLR3	=	$02C3	;player color 3
GPRIOR	=	$026F	;priority
SIZEP2	=	$D00A	;size player 2
SIZEP3	=	$D00B	;size player 3
HPOSP0	=	$D000	;pos player 0
HPOSP2	=	$D002	;pos player 2
HPOSP3	=	$D003	;pos player 3
HPOSM0	=	$D004	;pos missile 0
SIZEM	=	$D00C	;missile size
VDELAY	=	$D01C	;vertical delay
GRACTL	=	$D01D	;graphics ctrl
CONSOL	=	$D01F	;console keys
PMBASE	=	$D407	;P/M base addr
AUDF1	=	$D200	;audio freq 1
AUDF2	=	$D202	;audio freq 2
AUDF3	=	$D204	;audio freq 3
AUDF4	=	$D206	;audio freq 4
AUDC1	=	$D201	;audio volume 1
AUDC2	=	$D203	;audio volume 2
AUDC3	=	$D205	;audio volume 3
AUDC4	=	$D207	;audio volume 4
AUDCTL	=	$D208	;audio control
SKCTL	=	$D20F	;serial ctrl
RANDOM	=	$D20A	;random number
STRIG	=	$0284	;joystick trig 0
STICK	=	$0278	;joystick 0
PAGES	=	$06	;scrn block size
P0PF	=	$D004	;P0/PF collision
P1PF	=	$D005	;P1/PF collision
M0PL	=	$D008	;M0/PL collision
M1PL	=	$D009	;M1/PL collision
P0PL	=	$D00C	;P0/PL collision
P1PL	=	$D00D	;P1/PL collision
HITCLR	=	$D01E	;collision clear
PACTL	=	$D302	;port A control
; Page Zero equates
; -----------------
	*=	$80
SELPNT	*=	*+2	;menu select pnt
CONSAV	*=	*+1	;console save
CLOCK	*=	*+1	;local clock
SLINE	*=	*+1	;scroll line cnt
VOLUME	*=	*+1	;intro volume
DIRSW	*=	*+1	;vol direction
OPTION	*=	*+1	;OPTION key indx
OPTSW	*=	*+1	;OPTION switch
TRIG	*=	*+1	;Trigger option
DENS	*=	*+1	;starfield dens
SHIP	*=	*+1	;ship type
COME	*=	*+1	;comet enabled
UNIV	*=	*+1	;inverse univ
SOFSET	*=	*+1	;SELECT offset
TEMP	*=	*+4	;temp registers
GRPAGE	*=	*+2	;screen pointer 
GRP1	*=	*+2	;asteroid left
GRP2	*=	*+2	;asteroid right
GRP20P	*=	*+2	;scrn pntr -20
GRPX	*=	*+2	;player gr pntr
GRPM	*=	*+2	;missile gr pntr
FLASHC	*=	*+1	;univ flash cntr
FLASHF	*=	*+1	;univ flash flag
REVF	*=	*+1	;inv univ flag
HPOS	*=	*+1	;comet H pos
HDIR	*=	*+1	;comet H dir
HINC	*=	*+1	;comet H speed
VPOS	*=	*+1	;comet V pos
VDIR	*=	*+1	;comet V dir
VINC	*=	*+1	;comet V speed
DEAD	*=	*+2	;dead ship flg
COMETF	*=	*+1	;comet set flag
CSOUND	*=	*+1	;comet snd cntr
UNIVS	*=	*+1	;universe sound
ENDGAM	*=	*+1	;game over flag
SCORES	*=	*+2	;game scores
TRIGN	*=	*+2	;processed trigs
TRIGS	*=	*+2	;last triggers
ROTATE	*=	*+1	;rotate index
SCLOCK	*=	*+1	;score snd timer
VDEL	*=	*+1	;vert delay
MISSLE	*=	*+2	;shot flags
ROWAC	*=	*+2	;shot row acc
DELTAR	*=	*+2	;shot delta row
ENDPT	*=	*+2	;shot end point
ROWCRS	*=	*+2	;shot row cursor
ROWINC	*=	*+2	;shot row inc
COLAC	*=	*+2	;shot column acc
DELTAC	*=	*+2	;delta column
COLCRS	*=	*+2	;column cursor
COLINC	*=	*+2	;shot column inc
COUNTR	*=	*+2	;shot delta cnt
NEWCOL	*=	*+1	;shot end column
NEWROW	*=	*+1	;shot end row
OLDCOL	*=	*+1	;shot old column
OLDROW	*=	*+1	;shot old row
TEMPM	*=	*+1	;shot temporary
M0PLS	*=	*+2	;M0 col shadow
XPLR	*=	*+2	;ship X coords
YPLR	*=	*+2	;ship Y coords
; Redefined Character Set Data
; ----------------------------
CHARS	.BYTE	0,0,0,0,0,0,0,0
	.BYTE	0,0,0,0,$7B,50,50,50
	.BYTE	0,0,0,0,$60,$A0,$A0,32
	.BYTE	0,$7E,66,66,$7E,66,66,0
	.BYTE	0,$7E,64,64,64,64,$7E,0
	.BYTE	0,$7C,70,70,70,70,$7C,0
	.BYTE	0,$7E,64,$7C,64,64,$7E,0
	.BYTE	0,$7E,64,$7C,64,64,64,0
	.BYTE	0,$7E,64,64,78,66,$7E,0
	.BYTE	0,66,66,$7E,66,66,66,0
	.BYTE	0,$7E,24,24,24,24,$7E,0
	.BYTE	0,64,64,64,64,64,$7E,0
	.BYTE	0,$7E,66,66,66,66,66,0
	.BYTE	0,$7E,66,66,$7E,64,64,0
	.BYTE	0,$7E,66,66,$7E,76,70,0
	.BYTE	0,$7E,24,24,24,24,24,0
	.BYTE	0,66,66,66,90,90,$7E,0
	.BYTE	0,66,66,$7E,24,24,24,0
	.BYTE	$7E,$81,$BD,$A1
	.BYTE	$A1,$BD,$81,$7E
	.BYTE	0,$7E,66,66,66,66,$7E,0
	.BYTE	0,8,8,8,8,8,8,0
	.BYTE	0,$7E,2,$7E,64,64,$7E,0
	.BYTE	0,$7E,2,$7E,2,2,$7E,0
	.BYTE	0,66,66,$7E,2,2,2,0
	.BYTE	0,$7E,64,$7E,2,2,$7E,0
	.BYTE	0,$7E,64,$7E,66,66,$7E,0
	.BYTE	0,$7E,2,2,2,2,2,0
	.BYTE	0,$7E,66,$7E,66,66,$7E,0
	.BYTE	0,$7E,66,$7E,2,2,$7E,0
	.BYTE	0,0,0,0,0,0,0,0
	.BYTE	24,36,90,0,0,0,0,0
	.BYTE	0,0,24,60,60,24,0,0
	.BYTE	0,0,0,60,$7E,$7E,$7E,60
	.BYTE	0,0,0,0,$7E,$FF,$FF,$FF
	.BYTE	0,0,0,0,0,60,$7E,$7E
	.BYTE	0,0,0,0,0,0,24,60
	.BYTE	0,0,0,0,0,0,0,24
	.BYTE	0,0,0,0,0,0,0,0
	.BYTE	0,0,0,0,0,0,0,0
	.BYTE	0,0,0,0,0,0,0,0
	.BYTE	60,0,0,0,0,0,0,0
	.BYTE	$FF,$FF,$FF,$7E,0,0,0,0
	.BYTE	$7E,$7E,60,0,0,0,0,0
	.BYTE	60,24,0,0,0,0,0,0
	.BYTE	24,0,0,0,0,0,0,0
	.BYTE	0,24,24,24,24,60,$7E,90
	.BYTE	24,24,24,60
	.BYTE	$7E,$FF,$DB,0
	.BYTE	0,0,0,0,0,0,0,0
	.BYTE	0,66,66,66,66,66,$7E,0
	.BYTE	0,0,24,24,0,24,24,0
	.BYTE	0,66,66,66,66,36,24,0
	.BYTE	0,$7E,90,90,66,66,66,0
	.BYTE	0,70,76,$78,88,76,70,0
	.BYTE	$7E,66,66,0,66,66,$7E,0
	.BYTE	2,2,2,0,2,2,2,0
	.BYTE	62,2,2,60,64,64,$7C,0
	.BYTE	62,2,2,60,2,2,62,0
	.BYTE	66,66,66,60,2,2,2,0
	.BYTE	$7C,64,64,60,2,2,62,0
	.BYTE	$7C,64,64,60,66,66,$7E,0
	.BYTE	62,2,2,0,2,2,2,0
	.BYTE	$7E,66,66,60,66,66,$7E,0
	.BYTE	$7E,66,66,60,2,2,62,0
; Introduction Display List
; -------------------------
DISPI	.BYTE	$70,$67
	.BYTE	$27,$27,$27,$27
	.BYTE	$27,$27,$27,$27
	.BYTE	$27,$27,$27,$27
	.BYTE	$27,$07,$41+DLI
; Game Options Display List
; -------------------------
DISPO	.BYTE	$70,$70,$70,$46
	.BYTE	$07,$46
	.BYTE	$46
	.BYTE	$06,$06,$46
	.BYTE	$46
	.BYTE	$46
	.BYTE	$46
	.BYTE	$46
	.BYTE	$46
	.BYTE	$46
	.BYTE	$46
	.BYTE	$46
	.BYTE	$46
	.BYTE	$46
	.BYTE	$46
	.BYTE	$46
	.BYTE	$46
	.BYTE	$46
	.BYTE	$46
	.BYTE	$46
	.BYTE	$41
; Game Playfield Display List
; ---------------------------
DISPG	.BYTE	$70,$70,$70,$4F
	.DBYTE	15,15,15,15,15,15,15
	.DBYTE	15,15,15,15,15,15,15
	.DBYTE	15,15,15,15,15,15,15
	.DBYTE	15,15,15,15,15,15,15
	.DBYTE	15,15,15,15,15,15,15
	.DBYTE	15,15,15,15,15,15,15
	.DBYTE	15,15,15,15,15,15,15
	.DBYTE	15,15,15,15,15,15,15
	.DBYTE	15,15,15,15,15,15,15
	.DBYTE	15,15,15,15,15,15,15
	.DBYTE	15,15,15,15,15
	.BYTE	$70,$30,$47+DLI
	.BYTE	$30,$42
	.BYTE	$41
; Flying saucer in Intro Data
; ---------------------------
SAUCER	.BYTE	$18,$7E,$7E,$FF
	.BYTE	$FF,$7E,$7E,$18
WINDOW	.BYTE	$00,$00,$00,$55
	.BYTE	$55,$00,$00,$00
; Redefined Char Set Equates
; --------------------------
TMC	=	1
AC	=	3
CC	=	4
DC	=	5
EC	=	6
FC	=	7
GC	=	8
HC	=	9
IC	=	10
LC	=	11
NC	=	12
PC	=	13
RC	=	14
TC	=	15
WC	=	16
YC	=	17
CRC	=	18
N0C	=	19
BC	=	N0C+8
OC	=	N0C
SC	=	OC+5
SMK	=	N0C+10
SMK2	=	SMK+8
SHC	=	SMK2+8
MT	=	SHC+2
UC	=	MT+1
MC	=	VC+1
KC	=	MC+1
BX	=	KC+$41
N7C	=	KC+2
; Introduction Title Data
; -----------------------
	.BYTE	$FF,97
	.BYTE	+$80,RC,AC,CC,EC,0
	.BYTE	+$80,IC,NC,0,SC,PC
	.BYTE	+$80,AC,CC,EC
	.BYTE	TMC,TMC+1,$FF,131
	.BYTE	+$40,NC,0,BC,YC
	.BYTE	$FF,160
	.BYTE	+$C0,SC,0,0,BC,AC,CC
	.BYTE	$FF,197,CRC,0
	.BYTE	N0C+1,N0C+9,N0C+8
	.BYTE	N0C+4,$FF,230
	.BYTE	+$80,SHC,0,0,SHC
	.BYTE	$FF,246
	.BYTE	+$40,SHC+1,0,0,SHC+1
; PRESS OPTION Message Data
; -------------------------
PMSG	.BYTE	0,0,0,0,0,0,0,0,0
	.BYTE	+$C0,OC,NC,0,0
	.BYTE	0,0,0,0,0,0,0,0,0
; Options Screen Data
; -------------------
	.BYTE	+$C0,0,0,TC,COLC
TIMOPT	.BYTE	+$80,N0C+3,0
	.BYTE	+$40,OC,NC,COLC,0
	.BYTE	+$80,LC,EC,FC,TC,0
	.BYTE	+$40,COLC
	.BYTE	0,0,PC,LC,AC,YC,0
	.BYTE	RC,COLC,0,0,0,0,0,BX
	.BYTE	+$80,YC,COLC,0,0
	.BYTE	0,0,0,BX
	.BYTE	+$80,COLC
	.BYTE	0,0,0,0,0,0,0,BX
	.BYTE	0,0,0,0,0,0,BX
	.BYTE	0,0,0,0,BX
SB	.BYTE	BX,0,0,0,0,0,0,0
	.BYTE	0,0,0,0,0,0,0
TOPT	.BYTE	BX,0,0,0,0
	.BYTE	+$C0,EC,CC,TC,0
TOPT2	.BYTE	BX,0,0,0,0,0,0
	.BYTE	+$C0,LC,DC,SC,0
TOPT3	.BYTE	BX,0,0,0,0,0
TOPT4	.BYTE	BX,0,0,0
DOPT	.BYTE	BX,0,0,0,0,0
DOPT2	.BYTE	BX,0,0,0,0,0,0,0
	.BYTE	+$C0,EC,0
DOPT3	.BYTE	BX,0,0,0,0,0,0,0
	.BYTE	+$C0,EC,0
DOPT4	.BYTE	BX,0,0,0,0,0,0,0,0
SOPT	.BYTE	BX,0,0,0,0,0,0
	.BYTE	+$C0,EC,TC,SC,0
SOPT2	.BYTE	BX,0,0,0,0,0,0
	.BYTE	+$C0,RC,SC,0
COPT	.BYTE	BX,0,0,0,0,0
COPT2	.BYTE	BX,0,0,0,0,0,0
	.BYTE	+$C0,LC,EC,DC,0
UOPT	.BYTE	BX,0,0,0,0,0
UOPT2	.BYTE	BX,0,0,0,0,0
	.BYTE	N0C+2,IC,NC,EC,0,N0C+1
	.BYTE	N0C+9,N0C+8,N0C+4
	.BYTE	0,0,0,0
TRAMI	.BYTE	0,0,N0C,N0C,0,0,0
	.BYTE	+$C0,N7C,SMK+7,N7C
	.BYTE	0,0,0,N0C,N0C,0,0
TRAMN	.BYTE	3,0,0,0,0
NUMMSK	.BYTE	$1F,$1E,$1A,$18
	.BYTE	$1D,$1B,$33,$35,$30
MISIMA	.BYTE	3,0,3,1,1,1,1,3
	.BYTE	0,3,2,3,2,2,3,2
MIMAGE	.BYTE	0,0,0,0
SELMSK	.BYTE	3,3,1,1,1
SELMS2	.BYTE	0,4,4,2,2
SHIPS	.BYTE	0,$18,$3C,$3C,$18
	.BYTE	$5A,$7E,$5A,$42
	.BYTE	0,$18,$7E,$DB
	.BYTE	$7E,0,0,0,0,0
VDMSK	.BYTE	$10,$20,$01,$02
XSTRT	.BYTE	88,160
SCNOTE	.BYTE	$50,$30
COMETM	.BYTE	0,$3C,$7E,$7E
	.BYTE	$FF,$7E,$7E,$3C,0
CE3K	.BYTE	$C6,$46,$F6,$66,$26
CE3KN	.BYTE	$6C,$A2,$51,$40,$48
; DLI Routine
; -----------
DLIVEC	PHA		;save Acc
	INC	CLOCK	;increment clock
	LDA	RTCLOK	;system clock
	ASL	A	;times 2
	AND	#$CE	;mask color
	STA	PCOLR2	;saucer color
	PLA		;restore Acc
	RTI		;return
; Console Checker
; ---------------
CONC	LDA	CONSOL	;get console
	TAY		;to Y register
	EOR	CONSAV	;only different
	AND	CONSAV	;pressed keys
	STY	CONSAV	;save current
	CMP	#4	;OPTION test
	RTS		;return
; Beep Routine
; ------------
BUZZER	STA	AUDF2	;buzzer freq
	LDA	#$A4	;pure tone
	STA	AUDC2	;in tone 2
	LDY	#$C0	;beep counter
BZ	DEX		;decrement X
	BNE	BZ	;zero yet? No.
	STX	ATRACT	;poke attract
	DEY		;decrement Y
	BNE	BZ	;tone done? No.
	STY	AUDC2	;Yes. turn off
	RTS		;return
; Flying Saucer Routine
; ---------------------
DELAY	LDX	#0	;get zero
	LDA	#$A4	;pure tone
	STA	AUDC1	;enable tone 1
	STA	AUDC2	;enable tone 2
DL1	LDA	#$12	;1/5 sec count
DL2	CMP	CLOCK	;compare clock
	BNE	DL2	;match? No.
	JSR	CONC	;check console
	BNE	DL3	;OPTION key? No.
	PLA		;Yes. pull RTS
	PLA		;addr from stack
	JMP	STOPTS	;options menu
DL3	LDA	#0	;get zero
	STA	CLOCK	;init clock
	INX		;inc saucer pos
	TXA		;move to Acc
	STA	HPOSP3	;move saucer
	AND	#$FC	;window movement
	STA	HPOSP2	;do windows
	LSR	A	;times 2
	LSR	A	;times 4
	LSR	A	;times 8
	TAY		;index to displa
	LDA	PMSG,Y	;get text
	STA	DRAM+313,Y	;on screen
	TXA		;saucer position
	ASL	A	;times 2
	ASL	A	;times 4
	ASL	A	;times 8
	ASL	A	;times 16
	ASL	A	;times 32 whew!
	EOR	#$F0	;inverse hi bits
	STA	AUDF1	;saucer sound
	CLC		;clear carry
	ADC	#2	;weird sound
	STA	AUDF2	;with resonance
	TXA		;saucer position
	BNE	DL1	;off screen? No.
	STA	AUDC2	;sound 2 off
	STA	VOLUME	;saucer volume
	RTS		;return
; Move All P/M Off Screen
; -----------------------
CLRPM	LDX	#7	;8 objects 0-7
	LDA	#0	;zero position
	DEX		;decrement count
	BPL	CPM	;done? No.
	RTS		;return
; Turn Off All Sound
; ------------------
AUDOFF	LDA	#0	;get zero
	STA	AUDC1	;sound 1 off
	STA	AUDC2	;sound 2 off
	STA	AUDC3	;sound 3 off
	STA	AUDC4	;sound 4 off
	RTS		;return
; Program Execution Starts Here
; -----------------------------
RIS	LDA	#$3C	;cassette off
	STA	PACTL	;poke hardware
	LDA	# <DOT	;density lo
	STA	SELPNT	;select point lo
	LDA	# >DOT	;density hi
	STA	SELPNT+1	;select pnt hi
	LDA	#0	;init sound
	STA	AUDCTL	;audio control
I1	STA	CONSAV,X	;zero flags
	DEX		;decrement index
	BPL	I1	;done? No.
; System Reset Returns Here
; -------------------------
INTRO	LDA	#$29	;value to enable
	STA	SDMCTL	;narrow playfld
	LDA	#3	;value to turn
	STA	SKCTL	;off 2-tome mode
	LDA	# >MRAM	;high byte of
	STA	PMBASE	;P/M address
	LDA	#2	;value to
	STA	GRACTL	;enable players
	LDA	# <DLIVEC	;DLI addr lo
	STA	VDSLST	;DLI vector lo
	LDA	# >DLIVEC	;DLI addr hi
	STA	VDSLST+1	;DLI vector hi
	LDA	#$C0	;value to
	STA	NMIEN	;enable DLI's
	LDA	# >CHARS	;addr of
	STA	CHBAS	;character set
	LDA	#$C6	;value for
	STA	COLOR1	;medium green
	LDA	#$94	;value for
	STA	COLOR2	;dark blue
	LDA	#$04	;value for
	STA	PCOLR3	;dark grey
	LDA	#1	;value - player
	STA	SIZEP2	;double width
	STA	SIZEP3	;players set
	STA	GPRIOR	;PL has priority
	JSR	CLRPM	;remove PLayers
	STA	REVF	;rev screen flag
	STA	DIRSW	;sound direction
	JSR	AUDOFF	;sound off
	TAX		;zero index
I2	STA	DRAM,X	;clear display
	STA	DRAM+256,X	;page 2
	STA	DRAM+512,X	;page 3
	STA	MRAM+512,X	;player 2+3
	DEX		;decrement index
	BNE	I2	;done? No.
	LDX	#7	;move 8 bytes
I3	LDA	WINDOW,X	;saucer windows
	STA	MRAM+$0228,X	;player 2
	LDA	SAUCER,X	;saucer ship
	STA	MRAM+$02A8,X	;player 3
	DEX		;decrement index
	BPL	I3	;saucer done? No.
; Print Text Onto Display
; -----------------------
PTITL	INX		;increment index
	LDA	TITLE,X	;get text
	BEQ	STITL	;byte zero? Yes.
	TAY		;display index
P2	INX		;inc text index
	LDA	TITLE,X	;get text
	CMP	#$FF	;EOL flag
	STA	DRAM+256,Y	;on screen
	INY		;inc displa indx
	JMP	P2	;continue
; Scroll Text For Intro
; ---------------------
STITL	LDA	# <DISPI	;DL addr lo
	STA	SDLSTL	;DL pntr lo
	LDA	# >DISPI	;DL addr hi
	STA	SDLSTL+1	;DL pntr hi
	LDA	# >DRAM	;screen top hi
	LDA	#0	;get zero
	STA	ATRACT	;poke attract
	STA	VOLUME	;clear volume
S1	LDA	#$10	;16/60 sec count
S2	BIT	CLOCK	;check clock
	BEQ	S2	;time up? No.
	JSR	CONC	;console keys
	BNE	S2A	;OPTION key? No.
	JMP	STOPTS	;option menu
S2A	LDA	#0	;get zero
	STA	CLOCK	;reset clock
	INC	SLINE	;inc scroll cnt
	LDA	SLINE	;scroll count
	CLC		;clear carry
	ADC	DADR	;screen addr lo
	EOR	DIRSW	;sound direction
	STA	AUDF1	;rocket sound
	LDA	SLINE	;scroll count
	AND	#7	;use only 0..7
	ADC	#SMK+$C0	;smoke offset
	STA	DRAM+518	;put below both
	STA	DRAM+521	;rocket ships
	ADC	#8	;botm smk offset
	STA	DRAM+534	;put below top
	STA	DRAM+537	;smoke of ships
	LDA	SLINE	;scroll count
	CMP	#16	;check overflow?
	BNE	S3	;No. continue
	LDA	#0	;get zero
	STA	SLINE	;reset count
	STA	VSCROL	;vertical scroll
	INC	VOLUME	;raise volume
	LDA	DIRSW	;sound direction
	EOR	VOLUME	;EOR with volume
	ORA	#$80	;rough sounding
	STA	AUDC1	;rocket sound
	CLC		;clear carry
	ADC	#16	;line width
	STA	DADR	;new DL LMS lo
	BCC	S3	;overflow? No.
	INC	DADR+1	;inc LMS hi
	LDA	#2+>DRAM	;cmp scrn end
	CMP	DADR+1	;with LMS hi
	BNE	S4	;at end? No.
	JMP	INTRO	;Yes. do intro
S4	JSR	DELAY	;flying saucer
	LDA	#$20	;value for
	STA	AUDF1	;reset frequency
	LDA	#$8F	;full volume
	STA	AUDC1	;reset tone
	LDA	#$0F	;reverse sound
	STA	DIRSW	;sound direction
S3	LDA	SLINE	;scroll count
	STA	VSCROL	;vertical scroll
	JMP	S1	;continue
; Game Option Menu Routine
; ------------------------
STP	CMP	CLOCK	;period to go by
	BEQ	STP	;before start
	LDA	#$21	;value for
	STA	SDMCTL	;narrow playfld
	LDA	# <DISPO	;DL addr lo
	STA	SDLSTL	;displa list lo
	LDA	# >DISPO	;DL addr hi
	STA	SDLSTL+1	;displa list hi
	JSR	SCRCLR	;clr inv Univ
	JSR	CLRPM	;clear players
	STA	ATRACT	;poke attract
	STA	GRACTL	;no players
	JSR	AUDOFF	;sound off
	STA	FLASHF	;clr flash flag
	STA	REVF	;clr inv flag
	LDA	#$94	;color value for
	STA	COLOR2	;medium blue
	LDA	#4	;five notes 0-4
	STA	TEMP+3	;same index
STS	LDX	TEMP+3	;get index
	LDA	CE3K,X	;get color
	STA	COLOR1	;change color
	LDA	CE3KN,X	;get note
	JSR	BUZZER	;play note
	DEC	TEMP+3	;dec index
	BPL	STS	;done? No.
ST1	LDA	CH	;check keyboard
	AND	#$3F	;mask CTRL/SHIFT
	LDX	#9	;check for 0-9
ST1A	CMP	NUMMSK-1,X	;cmp keycode
	BEQ	ST1B	;numeric? Yes.
	DEX		;decrement index
	BNE	ST1A	;done? No.
	BEQ	ST1C	;Yes. continue
ST1B	TXA		;index is number
	STA	TRAMN	;store time
	CLC		;clear carry
	ADC	#N0C+$80	;display offset
	STA	TIMOPT	;show time opt
	TXA		;number again
	ADC	#N7C+$C0	;2nd char set
	STA	TRAMC	;game score line
	LDA	#$FF	;clear the
	STA	CH	;keyboard buffer
	TXA		;number again
	ASL	A	;times 2
	ASL	A	;times 4
	EOR	#$3F	;inverse here to
	JSR	BUZZER	;number sound
ST1C	JSR	CONC	;check console
	LSR	A	;check START key
	BCC	ST2	;START key? No.
	JMP	PLAYGM	;Yes. play game
; SELECT Key Handler
; ------------------
	BCC	ST3	;SELECT key? No.
	LDA	#$30	;Yes. do SELECT
	JSR	BUZZER	;key noise
	LDX	OPTION	;opt to change
	INC	TRIG,X	;inc option byte
	LDA	TRIG,X	;get option byte
	AND	SELMSK,X	;mask overflow
	STA	TRIG,X	;save opt byte
	ASL	A	;times 2
	TAX		;use as X index
	LDY	#0	;zero Y index
	LDA	MADR,X	;text addr lo
	STA	(SELPNT),Y	;LMS byte lo
	INY		;inc Y index
	LDA	MADR+1,X	;text addr hi
	STA	(SELPNT),Y	;LMS byte hi
	JMP	ST1	;continue
; OPTION Key Handler
; ------------------
	BCC	ST1	;OPTION key? No.
	LDA	#$10	;Yes. do OPTION
	JSR	BUZZER	;key sound
	LDX	#1	;reset text flag
ST4	STX	OPTSW	;option switch
	LDA	OPTION	;option counter
	ASL	A	;times 2
	ASL	A	;times 4
	ASL	A	;times 8
	ASL	A	;times 16
	TAX		;use as index
	LDY	#13	;do 14 bytes
ST4A	LDA	#$80	;get sign bit
	EOR	OL2+1,X	;flip sign
	STA	OL2+1,X	;save byte
	INX		;increment index
	DEY		;decrement count
	BPL	ST4A	;done? No.
	LDA	OPTSW	;option switch
	BNE	ST4B	;flipping done?
	JMP	ST1	;Yes. continue
ST4B	INC	OPTION	;inc option cntr
	LDA	OPTION	;option counter
	ASL	A	;times 2
	TAX		;use as index
	LDA	LADR-2,X	;DL LMS addr lo
	STA	SELPNT	;select pntr lo
	LDA	LADR-1,X	;DL LMS addr hi
	STA	SELPNT+1	;select pntr hi
	LDX	OPTION	;option counter
	LDA	SELMS2,X	;offset table
	ADC	SOFSET	;present offset
	STA	SOFSET	;new offset
	LDX	#0	;get zero
	LDA	OPTION	;option counter
	CMP	#5	;range: 0..4
	BNE	ST4	;overflow? No.
	STX	OPTION	;reset counter
	STX	SOFSET	;reset offset
	JMP	ST4	;continue
; Asteroid Field Initializer
; --------------------------
; Initialize pointers
; -------------------
LDGRRT	LDA	# <ASTR	;asteroid right
	STA	GRPAGE	;field addr lo
	TAY		;use as index
	LDA	# >ASTR	;asteroid right
	STA	GRPAGE+1	;field addr hi
	LDA	#PAGES	;# of 256 byte
	STA	TEMP+2	;blocks to move
	RTS		;return
; Generate Asteroid Field Bytes
; -----------------------------
RANWRD	LDA	#2	;# 4-bit nibbles
	STA	TEMP	;save counter
RANW0	CPX	RANDOM	;with density
	ROL	TEMP+1	;carry to bit 0
	ASL	TEMP+1	;to bit 1
	ASL	TEMP+1	;to bit 2
	ASL	TEMP+1	;to bit 3
	DEC	TEMP	;nibble count
	BNE	RANW0	;byte done? No.
	LDA	TEMP+1	;move byte to
	STA	(GRPAGE),Y	;graphic area
	RTS		;return
; Fill Workspace With Graphics
; ----------------------------
RANFIL	JSR	LDGRRT	;init pointers
	ASL	TEMP+2	;blocks times 2
	LDX	DENS	;get density
RANF0	JSR	RANWRD	;make starfield
	INY		;inc block index
	BNE	RANF0	;block done? No.
	INC	GRPAGE+1	;inc page pntr
	DEC	TEMP+2	;dec block cntr
	BNE	RANF0	;done? No.
; Shift ASTR Space To Right
; -------------------------
	DEC	GRPAGE+1	;dec page pntr
	LDA	#PAGES	;get block count
	STA	TEMP+2	;store count
RANF1	DEY		;dec index
	LDA	(GRPAGE),Y	;asteroid byte
	LSR	A	;force to odd
	STA	(GRPAGE),Y	;replace byte
	TYA		;exam index
	BNE	RANF1	;index=0? No.
	DEC	GRPAGE+1	;back up pntr
	DEC	TEMP+2	;decrement count
	BNE	RANF1	;Done? No.
	RTS		;return
; Ship Scoring Routine
; --------------------
SCORE	LDY	#10	;clr top 16 bytes
SC0	STA	PM0,Y	;of player 0
	STA	PM1,Y	;and player 1
	DEY		;decrement index
	BPL	SC0	;done? No.
	LDA	XSTRT,X	;start position
	STA	XPLR,X	;to player pos
	STA	HPOSP0,X	;set hardware
SCOREM	TXA		;save X to Acc
	PHA		;push Acc
	LDA	SCPNT,X	;score Y pos
	TAX		;use as index
	INC	TRAM,X	;increment score
	LDA	TRAM,X	;get score byte
	CMP	#N0C+10	;value over 9?
	BCC	SC1	;No. skip
	LDA	#N0C	;get zero char
	STA	TRAM,X	;to 1's position
	INC	TRAM-1,X	;inc 10's pos
SC1	PLA		;pull Acc
	TAX		;get X indx back
	LDA	SCNOTE,X	;score sound
	STA	AUDF3	;set frequency
	LDA	#$AE	;loud sound
	STA	AUDC3	;set volume
	LDA	#3	;value for
	STA	SCLOCK	;sound duration
	DEC	SCORES,X	;dec max score
	BNE	SC2	;from 99 to zero
	LDA	#0	;99 points so
	STA	ENDGAM	;end the game
SC2	LDA	#$FF	;value to return
	STA	HITCLR	;clear collision
	RTS		;return
; Ship Graphics Rotation
; ----------------------
ROTOR	TXA		;move X to Acc
	PHA		;save X
	LDA	CLOCK	;get clock
	ROR	A	;test bit 0
	BCS	RT2	;bit=1? Yes.
	DEC	ROTATE	;rotation index
	BPL	RT1	;rotate<0? No.
	LDA	#2	;reset value for
	STA	ROTATE	;rotation index
RT1	LDX	ROTATE	;get index
	LDA	ROTMSK,X	;spinner graphic
	STA	SHIPS+12	;saucer section
	AND	#$3C	;mask for rocket
	STA	SHIPS+2	;rocket upper
	LDA	ROTMSK+1,X	;next seq
	AND	#$3C	;mask for rocket
	STA	SHIPS+3	;rocket lower
	LDA	CLOCK	;get clock again
	AND	#$0E	;missile mask
	TAX		;use as index
	LDA	MISIMA,X	;missile image
	STA	MIMAGE+1	;image buffer
	LDA	MISIMA+1,X	;missile pic+1
	STA	MIMAGE+2	;image buffer+1
RT2	PLA		;pull Acc
	TAX		;restore X
	RTS		;return
; Countdown Timer Handler
; -----------------------
TIMER	DEC	TRAM+24	;1/10 sec timer
	BPL	TMX	;time up? No.
	LDA	#5	;Yes. value to
	STA	TRAM+24	;reset timer
	LDA	SCLOCK	;tic sound clock
	BEQ	RT3	;tic done? Yes.
	DEC	SCLOCK	;dec tic clock
	JMP	RT4	;continue
RT3	STA	AUDC3	;tic sound off
RT4	DEC	TRAM+12	;1/10 sec displa
	DEC	TRAM+23	;1/10 sec cntr
	BPL	TMX	;1 sec done? No.
	LDA	#N7C+$C9	;value to reset
	STA	TRAM+12	;1/10 sec displa
	LDA	#9	;value to reset
	STA	TRAM+23	;1/10 sec cntr
	LDA	SCLOCK	;sound clock
	BNE	RT5	;in use? Yes.
	LDA	#$A4	;value for
	STA	AUDC3	;pure tone
	LDA	#$40	;value for
	STA	AUDF3	;medium freq
RT5	DEC	TRAM+10	;one's display
	DEC	TRAM+22	;one's counter
	BPL	TMX	;10 sec up? No.
	LDA	#N7C+$C9	;value to reset
	STA	TRAM+10	;one's display
	LDA	#9	;value to reset
	STA	TRAM+22	;one's counter
	DEC	TRAM+9	;ten's display
	DEC	TRAM+21	;ten's counter
	BPL	TMX	;minute up? No.
	LDA	#N7C+$C5	;value to reset
	STA	TRAM+9	;ten's display
	LDA	#5	;value to reset
	STA	TRAM+21	;ten's counter
	DEC	TRAM+7	;minute display
	DEC	TRAM+20	;minute counter
TMX	PHP		;save flags
	LDA	SCLOCK	;if score sound
	ORA	COUNTR	;or missile 0/1
	ORA	COUNTR+1	;active?
	BNE	TMXX	;Yes. skip next
	LDA	DEAD	;either ship 0
	AND	DEAD+1	;or ship 1
	BEQ	TMXX	;dead? Yes.
	LDA	MISSLE	;OR flags for
	ORA	MISSLE+1	;projectiles
	BEQ	TMXX	;any active? No.
	LDA	#$28	;projectile snd
	STA	AUDC3	;to hardware
	LDA	CLOCK	;60 cycle clock
	LSR	A	;make 30 cycles
	AND	#$07	;only 0..7
	ORA	#8	;8..15
	STA	AUDF3	;boomerang sound
TMXX	PLP		;restore flags
	RTS		;return
; Collision Handler
; -----------------
SMASH	LDA	M1PL	;missile 1 to
	AND	#1	;player 0 ship
	BNE	HITP0	;collision? Yes.
	LDA	P0PF	;player 0 to
	AND	#4	;playfield 2 or
	ORA	P0PL	;to any player
	BEQ	PLR1	;collision? No.
	LDA	TRIGN	;trigger option
	CMP	#1	;shield in use?
	BEQ	PLR1	;Yes. ship safe
HITP0	LDA	#0	;value for ship
	STA	DEAD	;being shot down
PLR1	LDA	M0PL	;missile 0 to
	AND	#2	;player 1 ship
	BNE	HITP1	;collision? Yes.
	LDA	P1PF	;player 1 to
	AND	#4	;playfield 2 or
	ORA	P1PL	;to any player
	BEQ	HITX	;collision? No.
	LDA	TRIGN+1	;trigger option
	CMP	#1	;shield in use
	BEQ	HITX	;Yes. ship safe
HITP1	LDA	#0	;value for ship
	STA	DEAD+1	;being shot down
HITX	RTS		;return
; Space Boomerang Handler
; -----------------------
MISFLY	LDA	MISSLE,X	;missile status
	BNE	HITX	;active? Yes.
	LDA	TRIGN,X	;trigger value
	CMP	#2	;shots enabled
	BEQ	MISF	;Yes. continue
	STA	TRIGS,X	;put shadow
	RTS		;return
; Set up Launch Coordinates
; -------------------------
MISF	CMP	TRIGS,X	;compare shadow
	BEQ	HITX	;same? Yes.
	STA	TRIGS,X	;put shadow
	STA	MISSLE,X	;enable missile
	CLC		;clear carry
	LDA	XPLR,X	;ship X coord
	ADC	#2	;get ship center
	STA	OLDCOL	;X plot coord
	STA	COLCRS,X	;shot current X
	LDA	YPLR,X	;ship Y coord
	STA	OLDROW	;Y plot coord
	INC	OLDROW	;ship top
	STA	ROWCRS,X	;shot current Y
	INC	ROWCRS,X	;plot coord
	TXA		;player index
	BEQ	MIS1	;player 0? Yes.
; Player 0 is target
; ------------------
	LDA	XPLR	;enemy X coord
	ADC	#2	;ship center
	STA	NEWCOL	;destination X
	LDA	YPLR	;enemy Y coord
	JMP	MIS2	;skip next
; Player 1 is target
; ------------------
MIS1	LDA	XPLR+1	;enemy X coord
	ADC	#2	;ship center
	STA	NEWCOL	;destination X
	LDA	YPLR+1	;enemy Y coord
MIS2	STA	NEWROW	;destination Y
	INC	NEWROW	;ship top
	LDA	#1	;init value for
	STA	ROWINC,X	;Y increment
	STA	COLINC,X	;X increment
	SEC		;set carry
	LDA	NEWROW	;Y to coord
	SBC	OLDROW	;Y from coord
	STA	DELTAR,X	;delta Y
	BCS	MIS3	;shot down? Yes.
	LDA	#$FF	;value = -1
	STA	ROWINC,X	;move up
	EOR	DELTAR,X	;get absolute
	STA	DELTAR,X	;value for
	INC	DELTAR,X	;delta Y
MIS3	SEC		;set carry
	LDA	NEWCOL	;X to coord
	SBC	OLDCOL	;X from coord
	STA	DELTAC,X	;delta X
	BCS	MIS4	;to right? Yes.
	LDA	#$FF	;value = -1
	STA	COLINC,X	;move left
	EOR	DELTAC,X	;get absolute
	STA	DELTAC,X	;value for
	INC	DELTAC,X	;delta X
MIS4	LDA	#0	;init value for
	STA	COLAC,X	;X accumulator
	STA	ROWAC,X	;Y accumulator
	LDA	DELTAC,X	;get delta X
	STA	ENDPT,X	;line length
	LDA	#$0F	;init value for
	STA	COUNTR,X	;draw iteration
	LDA	DELTAR,X	;get delta Y
	CMP	ENDPT,X	;bigger than
	BCC	MIS5	;delta X? No.
	STA	ENDPT,X	;store new value
	LSR	A	;delta Y / 2
	STA	COLAC,X	;X coord Acc
	RTS		;return
MIS5	LDA	ENDPT,X	;get delta X
	LSR	A	;divide by 2
	STA	ROWAC,X	;Y coord Acc
	RTS		;return
; Game Interrupt Service Routine
; ------------------------------
GISR	PHA		;save Acc
	JSR	SMASH	;test collisions
	JSR	ROTOR	;animate ships
	INC	CLOCK	;increment clock
	CLC		;clear carry
	LDA	UNIVS	;universe sound
	ADC	#$30	;change sound
	STA	UNIVS	;replace sound
	STA	AUDF2	;make sound
	LDA	ENDGAM	;game end flag
	BNE	GI7	;game over? No.
	JMP	GI99	;end it now!
; Ship Noise Generation
; ---------------------
GI7	LDA	#8	;medium grey
	STA	COLPF1	;set color
	TXA		;move X to Acc
	PHA		;save X
	LDX	#15	;neutral stick
	LDA	DEAD	;player 0 status
	BNE	GI70	;dead? No.
	STX	STICK	;stick to center
GI70	LDA	DEAD+1	;player 1 status
	BNE	GI71	;dead? No.
	STX	STICK+1	;stick to center
GI71	LDA	STICK	;check if either
	AND	STICK+1	;stick pushed by
	CMP	#15	;comparing w/15
	LDA	#$81	;rumble noise
	BCS	GI03	;both 15? Yes.
	LDA	TRIGN	;trigger opt 0
	ORA	TRIGN+1	;trigger opt 1
	CMP	#3	;warp speed test
	LDA	#$88	;loud warp sound
	BCS	GI03	;warp? Yes.
	LDA	#$84	;med engine roar
GI03	STA	AUDC4	;make engine snd
	LDA	#24	;warp frequency
	BCS	GI30	;warp? Yes.
	LDA	#32	;normal rockets
GI30	STA	AUDF4	;set frequency
	LDX	#0	;init value for
	STX	VDEL	;vertical delay
	INX		;make X = 1
	LDA	M0PL	;missile 0 to
	STA	M0PLS	;PL collisions
	LDA	M0PL+1	;missile 1 to
	STA	M0PLS+1	;PL collisions
	LDA	TRIGN	;trigger opt 0
	ORA	TRIGN+1	;trigger opt 1
	CMP	#1	;check shields
	BNE	MOVE2	;shields on? No.
	LDA	RANDOM	;random number
	AND	#$1F	;only 0..31
	ORA	#$20	;only 32..63
	STA	AUDF4	;shield sound
	LDA	#$A6	;value for
	STA	AUDC4	;shield volume
MOVE2	JSR	TRIGR	;read trigger
	LDA	DEAD,X	;player status
	BEQ	MOVEX	;dead? Yes.
	LDA	TRIGN,X	;trigger value
	CMP	#1	;shields in use?
	BEQ	MOVEX	;Yes. skip next
	JSR	MISFLY	;move missile
	LDA	CLOCK	;get clock value
	ROR	A	;bit 0 to carry
	BCC	MOVE2X	;even? Yes.
	LDA	TRIGN,X	;trigger value
	CMP	#3	;warp drive?
	BNE	MOVEX	;No. skip next
; Joystick Handler
; ----------------
MOVE2X	LSR	STICK,X	;check joystick
	BCS	MOVED	;stick up? No.
	DEC	YPLR,X	;move ship up
MOVED	LSR	STICK,X	;check joystick
	BCS	MOVEL	;stick down? No.
	INC	YPLR,X	;move ship down
MOVEL	LDA	SHIP	;get ship type
	BEQ	MOVEX	;U/D rocket? Yes.
	LSR	STICK,X	;check joystick
	BCS	MOVER	;stick left? No.
	DEC	XPLR,X	;move ship left
MOVER	LSR	STICK,X	;check joystick
	BCS	MOVEX	;stick right? No.
	INC	XPLR,X	;move ship right
MOVEX	LDA	XPLR,X	;ship X coord
	CMP	#$30	;past left
	BCS	MOVEX3	;border? No.
	LDA	#$30	;set to border
MOVEX3	CMP	#$C8	;past right
	BCC	MOVEX4	;border? No.
	LDA	#$C7	;set to border
MOVEX4	STA	XPLR,X	;save X coord
	STA	HPOSP0,X	;position ship
	STY	TEMP+3	;save Y
	LDA	DEAD,X	;ship status
	BMI	MOVX4	;alive? Yes.
	LDA	CLOCK	;get clock value
	ROR	A	;test bit 0
	BCS	MOV4	;clock odd? Yes.
	ASL	A	;restore clock
	AND	#$F6	;max 7 brightness
	STA	PCOLR0,X	;make ship color
	LDA	SCLOCK	;score snd count
	BNE	MOV4	;sound on? Yes.
	LDA	CLOCK	;get clock value
	AND	#$07	;make 0..7
	ORA	#$C8	;make $C8..$CF
	STA	AUDC3	;sound volume
	LDA	RANDOM	;random number
	AND	#$1F	;make 0..31
	ORA	#$20	;make 32..63
	STA	AUDF3	;weird sound
MOV4	INC	YPLR,X	;move ship down
MOVX4	LDA	YPLR,X	;ship Y coord
	BNE	MOVEX6	;screen top? No.
	JSR	SCORE	;increment score
MOVEX6	CMP	#192	;screen bottom?
	BCC	MOVEX5	;No. skip next
	LDA	DEAD,X	;ship status
	BNE	MOVX6	;ship dead? No.
	LDA	XPLR,X	;ship X coord
	CMP	XSTRT,X	;compare w/start
	BEQ	MOVX6A	;equal? Yes.
	INC	XPLR,X	;move ship right
	BCC	MOVX6	;ok? Yes. else
	DEC	XPLR,X	;move ship left
	DEC	XPLR,X	;move ship left
	BNE	MOVX6	;skip next
MOVX6A	LDA	#$FF	;value for
	STA	DEAD,X	;working ship
	STA	HITCLR	;clr collisions
	LDA	PCOLRS,X	;value for
	STA	PCOLR0,X	;ship color
	LDA	SCLOCK	;score snd clock
	BNE	MOVX6	;sound on? Yes.
	STA	AUDC3	;zero sound
MOVX6	LDA	#191	;value for
MOVEX5	STA	YPLR,X	;init Y coord
	CPX	#1	;ship 1?
	ROR	A	;carry=1 if Yes.
	STA	GRPX	;PM graphic pntr
	BCC	MOVEX7	;coord even? Yes.
	LDA	VDEL	;vertical delay
	ORA	VDMSK,X	;delay mask
	STA	VDEL	;new V.delay
MOVEX7	TXA		;move X to Acc
	PHA		;save X
	CLC		;clear carry
	LDA	DEAD,X	;ship status
	BEQ	MOVX7A	;ship dead? Yes.
	LDA	RANDOM	;random number
	AND	#$0F	;make 0..15
	ORA	PCOLRS,X	;add ship color
	STA	PCOLR0,X	;new ship color
	LDA	TRIGN,X	;check trigger
	CMP	#1	;for shields
	SEC		;set carry
	BEQ	MOVX7A	;shields? Yes.
	CLC		;clear carry
	LDA	PCOLRS,X	;ship color
	STA	PCOLR0,X	;set color
MOVX7A	LDY	#9	;do 10 bytes
	LDX	#9	;rocket offset
	LDA	SHIP	;get ship type
	BEQ	MOVEXD	;rocket? Yes.
	LDX	#18	;saucer offset
MOVEXD	LDA	SHIPS,X	;ship graphic
	BCC	MVXD	;shields on? No.
	AND	RANDOM	;shield effect
MVXD	STA	(GRPX),Y	;put ship
	DEX		;graphic index
	DEY		;PM index
	BPL	MOVEXD	;done? No.
	PLA		;pull X
	TAX		;move Acc to X
	LDA	MISSLE,X	;missile status
	BEQ	MVXDM	;active? No.
	LDY	#1	;missile launcher
	LDA	#0	;no shot graphic
	STA	(GRPX),Y	;put ship
MVXDM	LDY	TEMP+3	;restore Y index
	DEX		;next ship
	BMI	MOVEX0	;done? Yes.
	JMP	MOVE2	;No. continue
MOVEX0	LDA	VDEL	;V.delay shadow
	STA	VDELAY	;vertical delay
	LDA	ENDGAM	;game status
	BEQ	MOVXE2	;game over? Yes.
	JSR	TIMER	;decrement time
	BPL	GI9	;time up? No.
	LDA	#N7C+$C0	;zero graphic
	STA	TRAM+7	;minutes display
	STA	TRAM+9	;10 sec display
	STA	TRAM+10	;seconds display
	STA	TRAM+12	;.1 sec display
MOVXE2	LDA	#121	;goto attract
	STA	ATRACT	;in 30 seconds
	LDA	#0	;get zero
	STA	ENDGAM	;end game
	STA	AUDC3	;sound off
	STA	AUDC4	;sound off
; Comet Mover Routine
; -------------------
GI9	PLA		;pull X
	TAX		;move Acc to X
GI99	LDA	HINC	;comet H speed
	AND	CLOCK	;mask with clock
	BEQ	GI91	;move comet? Yes.
GI90	PLA		;restore Acc
	RTI		;return
GI91	LDA	COMETF	;comet status
	BEQ	GI90	;active? No.
	TYA		;move Y to Acc
	PHA		;save Y
	TXA		;move X to Acc
	PHA		;save X
	LDA	HPOS	;comet H coord
	AND	VINC	;and w/V speed
	BNE	GI5	;move vert? No.
	LDA	VPOS	;comet V coord
	CLC		;clear carry
	ADC	VDIR	;add V direction
	AND	#$7F	;make 0..127 only
	STA	VPOS	;replace V coord
; Draw Comet Graphics
; -------------------
GI5	LDY	#13	;do 14 bytes
	LDX	VPOS	;comet V coord
GI0	LDA	RANDOM	;random number
	AND	COMETM,Y	;mask w/comet
	STA	PM2,X	;put player 2
	LDA	RANDOM	;random number
	AND	COMETM,Y	;do same thing
	STA	PM3,X	;put player 3
	INX		;inc player addr
	TXA		;move X to Acc
	AND	#$7F	;make 0..127
	TAX		;replace X
	DEY		;dec byte count
	BPL	GI0	;pic done? No.
	LDA	RANDOM	;random number
	AND	#$F0	;color only
	ORA	#$04	;brightness 4
	STA	PCOLR2	;player 2 color
	LDA	RANDOM	;random number
	AND	#$F0	;color only
	ORA	#$08	;brightness 8
	STA	PCOLR3	;player 3 color
	CLC		;clear carry
	LDA	HPOS	;comet H coord
	ADC	HDIR	;add H direction
	STA	HPOS	;new H coord
	STA	HPOSP2	;player 2 H pos
	STA	HPOSP3	;player 3 H pos
	STA	COMETF	;non 0 = enabled
; Generate Comet Sound
; --------------------
	INC	CSOUND	;comet snd freq
	LDA	ENDGAM	;game status
	BEQ	GIS	;game over? Yes.
	LDA	CSOUND	;comet snd freq
	CMP	#125	;value < 125
	BCS	GI2	;No. skip next
	LSR	A	;freq/2
	LSR	A	;freq/4
	STA	AUDF1	;set frequency
	CMP	#$18	;past peak?
	BCC	GI2	;No. skip next
	EOR	#$9F	;reverse volume
GIS	STA	AUDC1	;set volume
GI2	PLA		;pull X
	TAX		;move Acc to X
	PLA		;pull Y
	TAY		;move Acc to Y
	PLA		;pull Acc
	RTI		;return
; Joystick Trigger Processor
; --------------------------
TRIGR	LDA	STRIG,X	;get trigger
	LSR	A	;move to carry
	BCS	TRIGX	;pressed? No.
	LDA	TRIG	;trigger option
TRIGX	AND	DEAD,X	;ship status
	CMP	TRIGN,X	;same as last?
	BEQ	TRIG2	;Yes. skip next
	STA	HITCLR	;clr collisions
TRIG2	STA	TRIGN,X	;trig option
; Missile Mover Routine
; ---------------------
	LDA	MISSLE,X	;missile status
	BEQ	MMX	;fired? No.
	LDA	ROWCRS,X	;missile Y coord
	BNE	MM0	;zero? No.
	STA	MISSLE,X	;disable missile
MMX	RTS		;return
MM0	CLC		;clear carry
	LDA	DELTAR,X	;add delta Y
	ADC	ROWAC,X	;to Y Acc
	STA	ROWAC,X	;new Y Acc
	CMP	ENDPT,X	;cmp w/endpoint
	BCC	MM1	;change Y? No.
	SBC	ENDPT,X	;sub endpoint
	STA	ROWAC,X	;new Y Acc value
	CLC		;clear carry
	LDA	ROWINC,X	;add shot Y inc
	ADC	ROWCRS,X	;to Y coord
	STA	ROWCRS,X	;new Y coord
MM1	CLC		;clear carry
	LDA	DELTAC,X	;add delta X
	ADC	COLAC,X	;to X Acc
	STA	COLAC,X	;new X Acc
	CMP	ENDPT,X	;cmp w/endpoint
	BCC	MMP	;change X? No.
	SBC	ENDPT,X	;sub endpoint
	STA	COLAC,X	;new X Acc value
	CLC		;clear carry
	LDA	COLINC,X	;add shot X inc
	ADC	COLCRS,X	;to X coord
	STA	COLCRS,X	;new X coord
MMP	LDA	COUNTR,X	;iteration cnt
	BEQ	MMP1	;cnt done? Yes.
	LSR	A	;cnt div 2
	ORA	#$88	;weird sound
	STA	AUDC3	;make sound FX
	LDA	COUNTR,X	;get cnt again
	EOR	#$0F	;very weird FX
	ASL	A	;times 2
	ASL	A	;times 4
	ASL	A	;times 8
	STA	AUDF3	;set frequency
	DEC	COUNTR,X	;decrement cnt
MMP1	LDA	COLCRS,X	;shot X coord
	STA	HPOSM0,X	;PM horiz pos
	LDA	ROWCRS,X	;shot Y coord
	LSR	A	;2 line res
	BCC	MM00	;even line? Yes.
	PHA		;save PM Y coord
	ORA	VDMSK+2,X	;odd scan line
	STA	VDEL	;new shadow val
	PLA		;restore Y coord
MM00	ORA	# <PMM	;missiles start
	STA	GRPM	;set pointer lo
	LDA	M0PLS,X	;test if shot hit
	AND	MCMSK,X	;comet or other
	BNE	MME	;ship? Yes.
	LDA	COLCRS,X	;shot Y coord
	BEQ	MME	;off scrn? Yes.
	TYA		;move Y to Acc
	PHA		;save Y
	LDY	#3	;4 pic bytes
MM01	LDA	(GRPM),Y	;current pic
	AND	MISMSK,X	;erase old pic
	STA	TEMPM	;save temp
	LDA	MIMAGE,Y	;new pic data
	CPX	#1	;player 1 shot?
	BNE	MM03	;No. skip next
	ASL	A	;shift byte two
	ASL	A	;bits to left
MM03	ORA	TEMPM	;add saved data
	STA	(GRPM),Y	;new shot pic
	DEY		;dec pic index
	BPL	MM01	;pic done? No.
	PLA		;restore Y
	TAY		;move Acc to Y
	RTS		;return
; Erase Current Shot
; ------------------
MME	LDA	#0	;get zero value
	STA	MISSLE,X	;kill shot
	TYA		;move Y to Acc
	PHA		;save Y
	LDY	#3	;do 4 bytes
MME2	LDA	(GRPM),Y	;old shot pic
	AND	MISMSK,X	;erase shot
	STA	(GRPM),Y	;replace pic
	DEY		;next byte
	BPL	MME2	;done? No.
	LDA	M0PLS,X	;cmp collisions
	AND	MCMSK,X	;w/all but own
	BEQ	MME3	;score point? No.
	JSR	SCOREM	;inc score
MME3	PLA		;pull Y
	TAY		;move Acc to Y
	RTS		;return
; Initialize Playfield
; --------------------
PLAYGM	JSR	AUDOFF	;turn snd off
	STA	HITCLR	;clr collisions
	LDA	#$FF	;value for
	STA	DEAD	;ship 1 alive
	STA	DEAD+1	;ship 2 alive
	LDA	#$40	;value to
	STA	NMIEN	;enable VBI's
	LDA	#PAGES*2	;pages to zero
	STA	TEMP+2	;save in counter
	LDA	# <DRAM	;display addr lo
	STA	GRPAGE	;display pntr lo
	LDA	# >DRAM	;display addr hi
	STA	GRPAGE+1	;displa pntr hi
	LDA	# >PMM	;PM addr hi
	STA	GRPM+1	;PM pointer hi
	LDA	#$21	;value for
	STA	GPRIOR	;mulit-color PL
	STA	AUDF4	;engine sound
	LDA	#1	;value for
	STA	SIZEP2	;double width
	STA	SIZEP3	;comets enabled
	STA	ENDGAM	;game on
	LDA	#99	;max score value
	STA	SCORES	;player 1
	STA	SCORES+1	;player 2
	LDX	#24	;move 25 bytes
	DEX		;dec index
	BPL	PLA3	;done? No.
	LDA	# >PM0	;player addr hi
	STA	GRPX+1	;pntr hi byte
	JSR	SCRCLR	;clear inverse
	LDA	#$05	;value for
	STA	SIZEM	;missile sizes
	LDA	#0	;get zero
	STA	HPOS	;comet X coord
	STA	FLASHF	;inverse flag
	STA	COMETF	;comet flag
	STA	ATRACT	;attract mode
	STA	SCLOCK	;score sound
	STA	MISSLE	;missile 0 flag
	STA	MISSLE+1	;missile 1 flag
	TAY		;zero Y index
PLA0	STA	(GRPAGE),Y	;scrn byte=0
	INY		;inc Y index
	BNE	PLA0	;page done? No.
	INC	GRPAGE+1	;do next page
	DEC	TEMP+2	;page count
	BNE	PLA0	;all done? No.
	LDA	#191	;init Y coord of
	STA	YPLR	;ship 1
	STA	YPLR+1	;ship 2
	TYA		;get zero
PLA1	STA	PMM,Y	;zero missiles
	STA	PM0,Y	;player 0+1
	STA	PM2,Y	;player 2+3
	INY		;next byte
	BNE	PLA1	;page done? No.
	JSR	RANFIL	;put asteroids
	LDX	#1	;do 2 players
PLA11	LDA	XSTRT,X	;ship X start
	STA	HPOSP0,X	;set hardware
	STA	XPLR,X	;and shadow
	DEX		;next ship
	BPL	PLA11	;done? No.
	INX		;make it a one
	STX	COLOR2	;black
	STX	TEMP+1	;zero temporary
	LDA	#$2E	;value for
	STA	SDMCTL	;P/M enable
	STA	COLOR1	;bright orange
	LDA	# >PM	;set up P/M
	STA	PMBASE	;base address
	LDA	#3	;value to
	STA	GRACTL	;enable P/M
	LDA	#$C4	;green for
	STA	PCOLR0	;first ship
	LDA	#$34	;red/orange for
	STA	PCOLR1	;second ship
	LDA	# <GISR	;DLI addr lo
	STA	VDSLST	;DLI pntr lo
	LDA	# >GISR	;DLI addr hi
	STA	VDSLST+1	;DLI pntr hi
	LDA	# <DISPG	;DL addr lo
	STA	SDLSTL	;DL pntr lo
	LDA	# >DISPG	;DL addr hi
	STA	SDLSTL+1	;DL pntr hi
	LDA	#$C0	;value to
	STA	NMIEN	;enable DLI's
; Game Loops Here, Loops Here...
; ------------------------------
ASHIFT	JSR	LDGRRT	;set up pointers
	ROR	TEMP+1	;get saved carry
	BCC	ART0	;bit #1=0? Yes.
	LDA	(GRPAGE),Y	;get byte
	ORA	#$80	;set high bit
	CLC		;clear carry
	BCC	ART2	;skip next
ART0	LDA	(GRPAGE),Y	;get byte
ART2	ROR	A	;rotate right
	STA	(GRPAGE),Y	;replace byte
	INY		;next byte
	BNE	ART0	;page done? No.
	INC	GRPAGE+1	;inc page addr
	DEC	TEMP+2	;dec page count
	BNE	ART0	;pages done? No.
	LDA	#PAGES	;pages to rotate
	STA	TEMP+2	;put someplace
	LDA	# <ASTL	;area to shift
	STA	GRPAGE	;gr pntr lo
	LDA	#PAGES-1+>ASTL	;hi addr
	STA	GRPAGE+1	;gr pntr hi
ALF1	DEY		;dec Y index
	LDA	(GRPAGE),Y	;get graphic
	ROL	A	;move to left
	STA	(GRPAGE),Y	;replace byte
	TYA		;test Y index
	BNE	ALF1	;Zero? No.
	DEC	GRPAGE+1	;dec hi addr
	DEC	TEMP+2	;dec page count
	BNE	ALF1	;pages done? No.
	ROL	TEMP+1	;save carry bit
	STA	GRP1	;zero low bytes
	STA	GRP2	;of these three
	STA	GRPAGE	;page zero pntrs
	LDA	# >ASTL	;scrn lf addr hi
	STA	GRP1+1	;scrn fl pntr hi
	LDA	# >ASTR	;scrn rt addr hi
	STA	GRP2+1	;scrn rt pntr hi
	LDA	# >DRAM	;display addr hi
	STA	GRPAGE+1	;displa pntr hi
	LDA	# <DRAM-20	;w/offset lo
	STA	GRP20P	;offset pntr lo
	LDA	# >DRAM-20	;w/offset hi
	STA	GRP20P+1	;offset pntr hi
	LDX	#76	;76 scan lines
ORA0	LDY	#19	;do 20 bytes
ORA1	LDA	(GRP1),Y	;to left field
	ORA	(GRP2),Y	;to right field
	STA	(GRPAGE),Y	;lf half scrn
	STA	(GRP20P),Y	;rt half scrn
	DEY		;dec index
	BPL	ORA1	;line done? No.
	LDA	GRP1	;lf field lo
	CLC		;clear carry
	ADC	#20	;20 byte offset
	STA	GRP1	;do next line of
	STA	GRP2	;asteroid fields
	BCC	ORA2	;overflow? No.
	INC	GRP1+1	;inc left, right
	INC	GRP2+1	;asteroid pntrs
ORA2	CLC		;clear carry
	LDA	GRPAGE	;graphic addr lo
	ADC	#40	;line offset
	STA	GRPAGE	;new lo addr
	BCC	ORA3	;overflow? No.
	INC	GRPAGE+1	;inc hi addr
ORA3	CLC		;clear carry
	LDA	GRP20P	;gr addr2 lo
	ADC	#40	;line offset
	STA	GRP20P	;new lo addr2
	BCC	ORA4	;overflow? No.
	INC	GRP20P+1	;inc high addr2
ORA4	DEX		;decrement index
	BNE	ORA0	;done? No.
	JSR	CONC	;check console
	JMP	STOPTS	;run option menu
; Inverse Universe Handler
; ------------------------
	BCC	FL0	;START pressed?
	JMP	PLAYGM	;Yes. restart
FL0	LDA	UNIV	;univ flag
	BEQ	COMET	;inverse? No.
	LDA	FLASHF	;flash flag
	BEQ	TRYFLA	;flash on? No.
	JSR	REVSCR	;flash screen
	DEC	FLASHC	;decrement count
	LDA	ENDGAM	;game over flag
	BEQ	FL1	;game over? Yes.
	LDA	FLASHC	;flash count
	LSR	A	;make volume
	ORA	#$A0	;make pure tone
FL1	STA	AUDC2	;universe sound
	LDA	FLASHC	;flash count
	BEQ	FLAEND	;done? Yes.
	ASL	A	;times 2
	ASL	A	;times 4
	ASL	A	;times 8
	EOR	#$FF	;flip bits
	STA	UNIVS	;save univ sound
	BNE	COMET	;continue
SCRCLR	LDA	REVF	;reverse flag
	ROR	A	;check bit 0
	BCC	SC9	;zero? Yes.
REVSCR	LDX	#4	;do colors 0..4
REV0	LDA	#$0F	;flip brightness
	EOR	COLOR0,X	;of colors
	STA	COLOR0,X	;replace values
	DEX		;decrement index
	BPL	REV0	;done? No.
	DEC	REVF	;clear flag
SC9	RTS		;return
TRYFLA	LDA	RANDOM	;random number
	AND	#$3F	;make 0..63
	BNE	COMET	;do flash? No.
	JSR	REVSCR	;Yes. flash scrn
	LDA	#$1F	;value for
	STA	FLASHC	;flash count
	STA	FLASHF	;flash flag
	BNE	COMET	;continue
FLAEND	STA	FLASHF	;flash univ off
	STA	AUDC2	;flash sound off
; Comet Mover
; -----------
COMET	LDA	COME	;comet flag
	BEQ	COMETX	;comets? No.
	LDA	COMETF	;comet on flag
	BEQ	TRYCOM	;on? No.
TRYCOM	LDA	RANDOM	;random number
	AND	#$3F	;make 0..63
	BNE	COMETX	;enable? No.
	STA	HINC	;comet H speed=0
	TAX		;initialize X=0
TRY0	STA	PM2,X	;clr players 2+3
	DEX		;decrement index
	BNE	TRY0	;done? No.
	STA	HPOSP2	;zero players 23
	STA	HPOSP3	;horizontal pos
	STA	CSOUND	;zero comet snd
TRY5	LDA	RANDOM	;random number
	AND	#3	;make 0..3
	CMP	#3	;allow only 0..2
	BCS	TRY5	;3? Yes, repeat
	STA	VDIR	;save 0..2
	DEC	VDIR	;make -1..1
	LDA	RANDOM	;random number
	AND	#3	;make 0..3
	TAX		;use as index
	LDA	#$1F	;init increment
TRY6	LSR	A	;divide by 2
	DEX		;decrement index
	BPL	TRY6	;done? No.
	STA	VINC	;vert increment
	LDA	ENDGAM	;end game flag
	BEQ	TRY7	;game over? Yes.
	LDA	#$88	;No. make sound
TRY7	STA	AUDC1	;comet sound
	LDA	RANDOM	;random number
	AND	#$3F	;make 0..63
	ADC	#16	;sorta 16..79
	STA	VPOS	;vert start pos
	LDX	#$FE	;value -2
	STX	COMETF	;comet on flag
	LDA	RANDOM	;random number
	BPL	TRY1	;flip a coin!
	LDX	#$02	;value +2
TRY1	STX	HDIR	;horiz direction
	LDA	RANDOM	;random number
	BPL	COMETX	;another coin!
	INC	HINC	;change speed
	JMP	ASHIFT	;continue
; Relocate program
; ----------------
RELOC	LDA	#$20	;$2000 load addr
	STA	GRP1+1	;from pntr hi
	LDA	#$10	;to $1000 addr
	STA	GRP2+1	;to pntr hi
	TAX		;move 16 pages
	LDA	#0	;value for
	STA	GRP1	;from pntr lo
	STA	GRP2	;to pntr lo
	TAY		;zero index
REL0	LDA	(GRP1),Y	;from byte
	STA	(GRP2),Y	;to byte
	DEY		;dec index
	BNE	REL0	;page done? No.
	INC	GRP1+1	;inc from hi
	INC	GRP2+1	;inc to hi
	DEX		;page count
	BNE	REL0	;done? No.
	JMP	RIS	;run program
	*=	$02E0	;RUN address
	.WORD	RELOC+$1000