COMPUTE! ISSUE 16 / SEPTEMBER 1981 / PAGE 86
Editor’s Note: We present in the following article, the most comprehensive Atari information ever published in a magazine. Because of its length, we had to make a tradeoff between source code size and magazine fit. Though small, it’s quite readable and is arranged for your ease of use. Enjoy it. — RCL.
Editor’s Note: This article provides a good game, a way to create cassette Boot tapes, and extensive material for study on the Atari’s machine language techniques. RM
Shoot is a machine language arcade style game that must be initialized on a 16K or greater Atari with or without DOS, but will run on ANY Atari, even an Atari 400 with 8K of RAM!
O.K. Before I tell you everything you ever wanted to know about how you too can write machine language video games for your Atari, I’m going to let you see just such a game. Stop reading this paragraph for a moment, and go and look at program 1. Program 1 is a Basic program that lakes about 6K to run. It will take the machine language program that I’ve encoded in the data statements and write it out onto a cassette tape. But this cassette tape is no ordinary cassette tape — it’s a Boot Tape.
What, you may ask, is a Boot Tape? It is the name of a tape that has a machine language program on it, along with information to tell the Atari how to load it into memory and where to jump to begin execution. Space Invaders is an example of a program that Atari offers in boot tape form. You can think of a boot tape as a do-it-yourself ROM Pac, since you need not have Basic (or any other cartridge) installed in your Atari at the time you ‘boot’ (short for boot-strap as in “to pull oneself up by one’s bool-straps”) the boot tape.
So what I want you to do now is warm up the Atari, type in the program in program 1, and run it. To those of you with only 8K: sorry, you’ll have to type this in on a friend’s machine. Be careful with those DATA statements! When you run the program, one of four things will happen:
In case 1, you can smile and move on to the next paragraph. In case two, check the line number mentioned in the error statement against the same line in program 1. They won’t be identical, so fix your mistake. In case 3, make sure that line 200 is entered correctly and also check that you’ve not forgotten to type in any of the data statements. In case 4, make sure that the string on line 300 is: ‘hhh’, reverse-video-asterisk, ‘LV’, reverse-video-d. If it is, then that’s not the problem which means you’ve come up with a totally new error, so congratulate yourself and try again.
Now, take the boot tape you just wrote and go over to ANY Atari computer. Open the lid and remove the ROM pack. Turn off all the peripherals (especially all 815’s, 810’s, and 850’s) except for the cassette recorder. Put the boot tape in the cassette recorder, rewind it, and press ‘Play’. Turn off the Atari 400/800, press down on the START Button, and turn the 400/800 back on. It should beep once, which is your signal to press the return key and wait. The boot tape will load into the RAM of your Atari. Once there, the cassette will stop and the game will begin!
First you will see a copyright message — must to make sure everybody knows that I wrote it — which will last for about 8 to 12 seconds. Then the message will disappear and three zeros will appear. The left (green) one is your score. The middle (red) one is your high score. The right (yellow) one is time remaining. Plug a joystick into controller jack 1 (far left) and press the start button.
Shazam! Eight rows of assorted sizes and colors of airplaned, helicopters and saucers will start flying hither and yon across the screen. Push the joystick left and right to aim the gun, press the button to fire the missile, then use the joystick to guide the missile into one of the planes. If you miss, try again. If you hit the plane it will explode and you will score some points: Helicopter — 5 points. Plane — 10 points, Saucer — 25 points. Clearing a rack of planes within 30 seconds gives you a bonus of 50 points. If you take more than 30 seconds to clear a rack of planes, the game will give you another full rack of planes immediately. For every 15 points you score you get an additional second of play time. When the timer goes to zero, your game ends, the high score is adjusted, and the program waits for you to press on the console buttons: Press START to restart the game. Press OPTION and SELECT down simultaneously to have the program make a copy of itself. If you do this, it will beep twice, wait until you’ve pressed return, and write a copy of itself to the cassette recorder. (THIS type of copying can be done on ANY size Atari, but first you have to have a working Boot Tape … which is why you’ve spent so much time typing in those data statements!).
Well, if you are afraid of machine language, or don’t want to program, you can stop reading this article at this point and go back to playing my game. But if you want to know how it works, read on …
I’ve included a listing of the “source code” [assembler input, usually documented, as here — Ed.] for SHOOT, but I bet that there won’t be enough free room to print it in its entirely. It IS commented very well, and all you assembly language freaks can take it and modify it as much as you like…. You might run into some size problems, since I wrote it on a much larger computer and just transferred the assembled object code over to the Atari, but with a bit of luck, you should be able to cut it down to size. One hint, most of the Atari equates aren’t used, so you needn’t bother to type them…. I’d bet that you’d need a disk and at least 32K to be able to start changing the code.
In general (and here I start using slang that no one who hasn’t read the Atari OS manuals will understand) there are three parts to a video game on the Atari — the setup, the main loop, and the end. In addition to these three parts are two other parts — the Vertical Blank Interrupt (VBI) and the Display List Interrupt (DLI).
The VBI occurs every sixtieth of a second and is used by the Atari to keep the realtime clock, do attract mode, update all sorts of counters, and so forth. The video game maker uses this time to move the players, update the scores, fire the shots, decrement the time left, and do sound effects.
The DLI occurs whenever the ANTIC chip reads a display list instruction that has the high bit set. The Atari OS doesn’t use the DLI, but the video game maker can use it to change character sets, playfield colors, and player positioning/width on the fly. In the Super Breakout cartridge, for example, all of the bricks are ‘really’ the same color, but carefully placed DLI’s in the display list change the hue of that color between rows of bricks. The octave bands in the Music Composer cartridge are also DLI generated.
In any event, here’s the poop on SHOOT: All the flying objects, AND the gun, are the same player, Player 0. Eleven display list interrupts are used to change the color of the sky/ground, the position of the planes/gun, the color of the planes/gun, and to check if the missile hit the previous plane. Since the sky/ground has no information in it, it need not take up any memory space, so the playfield display uses only the 20 characters in the score line at the top of the screen.
The vertical blank interrupt updates the score, awards bonus time, moves the gun, and fires and moves the missile. When the user runs out of time, a flag called STOP is set to tell the main program that the game is over. If a missile is in flight or the player is scoring points, this routine will also generate the appropriate sound effects.
The main body of the program actually has very little to do. First it draws the playfield, sets up the player missile graphics, knits the VBI and DLI handlers into the operating system, displays the copyright message and zeroes the scores. Then it waits for the user to press some console buttons. START starts the game and OPTION and SELECT save a copy to tape.
When the game is started, the main loop draws a set of planes, sets Count Down Timer #3 for thirty seconds, and waits for either the user to shoot down all the planes in the current rack, or the count down timer to expire, or the game to end. If the user shoots down all the planes within thirty seconds, 50 points are added to the value of the last plane shot down. When either 30 seconds are up, or all the planes are shot down, the main loop draws a whole new set of planes. This goes on until the user runs out of time.
When the user runs out of time (and, if he can shoot a whole rack off the screen in less than ten seconds, he, or she can play forever) the final score is compared with the high score, if the final score is higher than the high score it becomes the new high score. In either event, the program loops to the wait for user input section and the user may play another game.
Well, that’s SHOOT in a nutshell. I’ve hidden most of the gritty details in the comments to the code. Feel free to use any part of my code for a game of your own, with the provision that you don’t try to sell it! I’d bet that the VBI and the DLI handlers could be used in conjunction with Basic programs that take care of the slower details. For example, you might want to use the VBI to move a Pong ball and Paddle set while the Basic program took care of the scoring, playfield generation, instructions, and so forth. Best of Luck!
0 DIM H$(1),B$(2),AD$(4),A$(60),BUF$(1148)
1 POKOFF=4*1024-1
2 GOTO 100
10 IF H$>="0" AND H$<="9" THEN D=ASC(H$)-48:RETURN
12 D=ASC(H$)-55:RETURN
20 H$=B$(1,2):GOSUB 10:B=D:H$=B$(2,2):GOSUB 10:B=B*16+D:CHECK=CHECK+B:RETURN
30 B$=AD$(1,2):GOSUB 20:AD=B:B$=AD$(3,4):GOSUB 20:AD=AD*256+B:RETURN
100 GRAPHICS 0
110 TRAP 900:LINE=1000:LSUM=0
120 READ A$:IF A$="END" THEN 200
130 ? LINE:CHECK=0:B$=A$(1,2):GOSUB 20:NOB=B
140 AD$=A$(3,6):GOSUB 30:FAD=AD
150 FOR I=1 TO NOB:B$=A$(5+2*I,6+2*I):GOSUB 20
160 M=FAD+I-1-POKOFF:BUF$(M,M)=CHR$(B):NEXT I
165 SUM=CHECK-65536*INT(CHECK/65536)
170 AD$=A$(LEN(A$)-3,LEN(A$)):GOSUB 30
180 IF SUM<>AD THEN 900
185 LSUM=LSUM+SUM:LINE=LINE+10:GOTO 120
200 IF LSUM<>125120 THEN ? "Too many/few lines": END
205 CLOSE #1
210 OPEN #1,8,128,"C:"
220 IOCB=832+16
230 POKE IOCB+2,11
240 BUF=ADR(BUF$)
250 POKE IOCB+4,BUF-(INT(BUF/256)*256)
260 POKE IOCB+5,INT(BUF/256)
270 BUFLEN=LEN(BUF$)
280 POKE IOCB+8,BUFLEN-(INT(BUFLEN/256)*256)
290 POKE IOCB+9,INT(BUFLEN/256)
300 DUMMY=USR(ADR("hhh*LVd"),16)
310 CLOSE #1
320 END
900 ? "ERROR IN#";LINE:END
1000 DATA 1810000009001008101860A93C8D02D3A916850AA910850B604C4E06A9
1010 DATA 18101812707070460018F070F070F070F070F070F070F070F070F00DF0
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1230 DATA 18122886B4A5B7D016AD8402D011A5B4D00DA96285B4A5B30A0A180BE0
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1250 DATA 181258A9008D00D2A9308D02D2A280A9009DFF199D7F19CAD0F7A90CB3
1260 DATA 18127000A2089DFFCFCAD0FAA92E8D2F02A9188D07D4A9038D1DD00C27
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1350 DATA 181348B185B685B5A218A00020C513C8C008D0F8A207A0D0A9038D0C95
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1470 DATA 101468032056E4A90C9D42032056E460433A9B0652
1480 DATA END
1 ;-*-MIDAS-*-
2 .ENABLE LC
.NLIST SEQ
.TITLE SHOOT
.SBTTL by John H. Palevich
;
;
; "Shoot" -- inspired by the Atari VCS "Air Sea Battle" cartridge.
;
; Feel free to modify & give away. Don't even think of selling this.
; O.K. If you want to assemble this on your Atari, you'll have to
; change some things around. Most changes can be inferred from looking
; at the code that this assembler produced and figuring out what you'd
; have to type to get the Atari to do the same thing.
;
; Some hints, though:
; ^ means /256
; .= means *=
; .ASCII means .BYTE
; (in expressions) means the value of the program counter
;
; Lables shouldn't have ':'s.
;
; Colleen Operating System Equate File
;
E000 CHRORG = $E000 ;CHARACTER SET
E400 VECTBL = $E400 ;VECTOR TABLE
E4B0 VCTABL = $E480 ;RAM VECTOR INITIAL VALUE TABLE
E4A8 CIOORG = $E4A6 ;CENTRAL I/O HANDLER
E0D5 INTORG = $EC05 ;INTERRUPT HANDLER
E344 SIOORG = $E344 ;SERIAL I/O HANDLER
E0EA DSKORG = $E0FA ;DISK HANDLER
EE76 PRNORG = $EE7B ;PRINTER HANDLER
EF41 CASORG = $EF41 ;CASSETTE HANDLER
F0E3 MONORG = $F0E3 ;MONITOR/POWER UP MODULE
F3E4 KBDORG = $F3E4 ;KEYBOARD/DISPLAY HANDLER
;
;
;
;
; VECTOR TABLE
;
; HANLDER ENTRY POINTS ARE CALLED OUT IS THE FOLLOWING VECTOR
; TABLE. THESE ARE THE ADDRESSES MINUS ONE.
;
; Example for Editor
;
; E400 Open
; 2 Close
; 4 Get
; 8 Put
; B Status
; A Special
; C Jump to Power on initialization routine
;
;
;
E400 EDITRV = $E400 ;EDITOR
E410 SCRENV = $E410 ;TELEVISION SCREEN
E420 KEYBDV = $F420 ;KEYBOARD
E430 PRINTV = $E430 ;PRINTER
E440 CASETV = $E440 ;CASSETTE
;
; JUMP VECTOR TABLE
;
;THE FOLLOWING IS A TABLE OF JUMP INSTRUCTIONS
;TO VARIOUS ENTRY POINTS IN THE OPERATING SYSTEM
;
E450 DISKIV = $E450 ;disk initialization
E453 DSKINV = $E453 ;disk interface
E456 CIOV = $E456 ;central input output routine
0000 ICZERO = $0 ;proper values for X
0010 ICONE = $10 ;when calling CIOV for each
0020 ICTWO = $20 ;of the IO control Blocks
0030 ICTHRE = $30
0040 ICFOUR = $40
0060 ICFIVE = $50
0060 ICSIX = $60
0073 ICSEVE = $70
E459 SIOV = $E459 ;serial input output routine
E46C SETVBV = $E45C ;set system timers routine
; With respect to SETVBV. the call sequence is
; X = MSB of vector/timer
; Y = LSB of vector/timer
; A = # of vector to hack
0001 SETMR1 = 1 ;Timer 1
0002 SETMR2 = 2 ; 2
0003 SETMR3 = 3 ; 3
0004 SETMR4 = 4 ; 4
0005 SETMR5 = 5 ; 5
0006 SETIMM = 6 ;Immediate VBLANK
0007 SETDEF = 7 ;Deffered VBLANK
E45F SYSVBV = $E45F ;SYSTEM VERTICAL BLANK CALCULATIONS
F462 XITVBL = $E462 ;EXIT VERTICAL BLANK CALCULATIONS
E465 SIOINV = $E465 ;SERIAL INPUT OUTPUT INITIALIZATION
E468 SENDEV = $E468 ;SEND ENABLE ROUTINE
E46B INTINV = $E46B ;INTERRUPT HANDLER INITIALIZATION
E46E CIOINV = $E46E ;CENTRAL INPUT OUTPUT INITIALIZATION
E471 BLKBDV = $E471 ;BLACKBOARD MODE
E474 VARMSV = $E474 ;WARM START ENTRY POINT
E477 COLDSV = $E477 ;COLD START ENTRY POINT
E47A RBLOKV = $E47A ;CASSETTE READ BLOCK ENTRY POINT VECTOR
E47D CSOPIV = $E470 ;CASSETTE OPEN TOR INPUT VECTOR
;VCTABL = $E480
;
;
; OPERATING SYSTEM EQUATES
;
; COMMAND CODES FOR IOCBS
0003 OPEN = 3 ;OPEN FOR INPUT/OUTPUT
0005 GETREC = 5 ;GET RECORD (TEXT)
0007 GETCHR = 7 ;GET CHARACTER(S)
0009 PUTREC = 9 ;PUT RECORD (TEXT)
000B PUTCHR = $B ;PUT CHARACTER(S)
000C CLOSE = $C ;CLOSE DEVICE
000D STATIS = $D ;STATUS REQUEST
000E SPECIL = $E ;BEGINNING OF SPECIAL ENTRY COMMANDS
;
; SPECIAL ENTRY COMMANDS
0011 DRAWLN = $11 ;DRAW LINE
0012 FILLIN = $12 ;DRAW LINE WITH RIGHT FILL
0020 RENAME = $20 ;RENAME DISK FILE
0021 DELETE = $21 ;DELETE DISK FILE
0022 FORMAT = $22 ;FORMAT
0023 LOCKFL = $23 ;LOCK FILE TO READ ONLY
0024 UNLOCK = $24 ;UNLOCK LOCKED FILE
0025 POINT = $25 ;POINT SECTOR
0026 NOTE = $26 ;NOTE SECTOR
00FF IOCFRE = $FF ;IOCB "FREE"
;
; AUX1 EQUATES
; () INDICATES WHICH DEVICES USE BIT
0001 APPEND = $1 ;OPEN FOR WRITE APPEND (D). OR SCREEN READ (E)
0002 DIRECT = $2 ;OPEN FOR DIRECTORY ACCESS (D)
0004 OPNIN = $4 ;OPEN FOR INPUT (ALL DEVICES)
0008 OPNOT = $8 ;GPEN FOR OUTPUT (ALL DEVICES)
000C OPNINO = OPNIN+OPNOT ;OPEN FOR INPUT AND OUTPUT (ALL DEVICES)
0010 MXDMOD = $10 ;OPEN FOR MIXED MODE (E,S)
0020 INSCLR = $20 ;OPEN WITHOUT CLEARING SCREEN (E,S)
;
; DEVICE NAMES
;
0045 SCREDT = 'E ;SCREEN EDITOR (R/W)
004B KBD = 'K ;KEYBOARD (R ONLY)
0053 DISPLY = 'S ;SCREEN DISPIAY (R/W)
0050 PRINTR = 'P ;PRINTER (W ONLY)
0043 CASSET = 'C ;CASSETTE
004D MODEM = 'M ;MODEM
0044 DISK = 'D ;DISK
;
;
;
;
; OPERATING SYSTEM STATUS CODES
;
0001 SUCCES = $01 ;SUCCESSFUL OPERATION
;
0080 BRKABT = $80 ;BREAK KEY ABORT
0081 PRVOPN = $81 ;IOCB ALREADY OPEN
0082 NONDEV = $82 ;NON-EXISTANT DEVICE
0083 VRONLY = $83 ;IOCB OPENED FOR WRITE ONLY
0084 NVALID = $84 ;INVALID COMMAND
0085 NOIOPN = $85 ;DEVICE OR FILE NOT OPEN
0086 BADIOC = $86 ;INVALID IOCB NUMBER
0087 RDONLY = $87 ;IOCB OPENED FOR READ ONLY
0088 EOFERR = $88 ;END OF FILE
0089 TRNRCD = $89 ;TRUNCATED RECORD
008A TIMOUT = $8A ;PERIPHERAL TIME OUT
008B DNACK = $8B ;DEVICE DOES NOT ACKNOWLEDGE COMMAND
008C FRMERR = $8C ;SERIAL BUS FRAMING ERROR
008D CRSROR = $8D ;CURSOR OVERRANGE
008E OVRRUN = $8E ;SERIAL BUS DATA OVERRUN
008F CHKERR = $8F ;SERIAL BUS CHECKSUM ERROR
;
0090 DERRER = $90 ;PERIPHERAL DEVICE ERROR (OPERATION NOT COMPLETED)
0091 BADMOD = $91 ;BAD SCREEN MODE NUMBER
0092 FNCNOT = $92 ;FUNCTION NOT IMPLEMENTED IN HANDLER
0093 SCRMEM = $93 ;INSUFICIENT MEMORY FOR SCREEN MODE
;
;
;
;
;
; PAGE ZERO RAM ASSIGNMENTS
;
0000 LINZBS = $0000 ;LINBUG RAM (WILL BE REPLACED BY MONITOR RAM)
;
; THESE LOCATIONS ARE NOT CLEARED
0002 CASINI = $0002 ;CASSETTE INIT LOCATION
0004 RAMLO = $0004 ;RAM POINTER FOR MEMORY TEST
0006 TRAMSZ = $0006 ;TEMPORARY REGISTER FOR RAM SIZE
0007 TSTDAT = $0007 ;RAM TEST DATA REGISTER
;
; CLEARED ON COLD START ONLY
0008 WARMST = $0008 ;WARM START FLAG
0009 BOOTQ = $0009 ;SUCCESSFUL BOOT FLAG <WAS BOOT?>
000A DOSVEC = $000A ;DISK SOFTWARE START FLAG
000C DOSINI = $000C ;DISK SOFTWARE INIT ADDRESS
000E APPMHI = $000E ;APPLICATIONS MEMORY HI LIMIT
;
; CLEARED ON A COLD OR WARM START
0010 INTZBS = $0010 ;INTERRUPT HANDLER
0010 POKMSK = $0010 ;SYSTEM MASK FOR POKEY IRQ HANDLER
0011 BRKKEY = $0011 ;BREAK KEY FLAG
0012 RTCLOCK = $0012 ;REAL TIME CLOCK (IN 16 MSEC UNITS)
;
0015 BUFADR = $0015 ;INDIRECT BUFFER ADDRESS REGISTER
;
0017 ICCOMT = $0017 ;COMMAND FOR VECTOR
;
0018 DSKFMS = $0018 ;DISK FILE MANAGER POINTER
;
001A DSKUTL = $001A ;DISK UTILITIES POINTER
;
001C PTIMOT = $001C ;PRINTER TIME OUT REGISTER
0010 PBPNT = $001D ;PRINTER BUFFER POINTER
001E PBUFSZ = $001E ;PRINT BUFFER SIZE
001F PTEMP = $001F ;TEMPORARY REGISTER
;
0020 ZIOCB = $0020 ;ZERO PAGE I/O CONIROL BLOCK
0010 IOCBSZ = 16 ;NUMBER OF BYTES PER IOCB
0080 MAXIOC = 8*IOCBSZ ;LENGTH OF THE IOCB AREA
0020 IOCBAS = $0020
0020 ICHIDZ = $0020 ;HANDLER INDEX NUMBER (FF == IOCB FREE)
0021 ICDNOZ = $0021 ;DEVICE NUMBER (DRIVE NUMBER)
0022 ICCOMZ = $0022 ;COMMAND CODE
0023 ICSTAZ = $0023 ;STATUS OF LAST IOCB ACTION
0024 ICBALZ = $0024 ;BUFFER ADDRESS LOW BYTE
0025 ICBAHZ = $0025 ;BUFFER ADDRESS HIGH BYTE
0026 ICPTLZ = $0026 ;PUT BYTE ROUTINE ADDRESS - 1
0027 ICPTHZ = $0027 ;
0028 ICBLLZ = $0028 ;BUFFER LENGTH LOW BYTE
0029 ICBLHZ = $0029
002A ICAX1Z = $002A ;AUXILIARY INFORMATION FIRST BYTE
002B ICAX2Z = $002B
002C ICSPRZ = $002C ;TWO SPARE BYTES (CIO LOCAL USE)
002E ICIDNO = ICSPRZ+2 ;IOCB NUMBER X 16
002F CIOCHR = ICSPRZ+3 ;CHARACTER BYTE FOR CURRENT OPERATION
;
0030 STATUS = $0030 ;INTERNAL STATUS STORAGE
0031 CHKSUM = $0031 ;CHECKSUM (SINGLE BYTE SUM WITH CARRY)
0032 BUFRLO = $0032 ;POINTER TO DATA BUFFER (LO BYTE)
0033 BUFRHI = $0033 ;POINTER TO DATA BUFFER (HI BYTE)
0034 BFENLO = $0034 ;NEXT BYTE PAST END OF DATA BUFFER (LO BYTE)
0035 BFENHI = $0035 ;NEXT BYTE PAST EHD OF DATA BUFFER (HI BYIE)
0036 CRETRY = $0036 ;NUMBER OF COMMAND FRAME RETRIES
0037 ORETRY = $0037 ;NUMBER OF DEVICE RETRIES
0038 BUFRFL = $0038 ;DATA BUFFER FULL FLAG
0039 RECVDN = $0039 ;RECIEVE DONE FLAG
003A XMTDON = $003A ;TRANSMISSION DONE FLAG
003B CHKSNT = $003B ;CHECKSUM SENT FLAG
003C NOCKSM = $003C ;NO CHECKSUM FOLLOWS DATA FLAG
;
;
003D BPTR = $003D
003E FTYPE = $003E
003F FEOF = $003F
0040 FREQ = $0040
0041 SOUNDR = $0041 ;NOISY I/O FLAG (ZERO IS QUIET)
0042 CRITIC = $0042 ;DEFINES CRITICAL SECTION (CRITICAL IF NON-ZERO)
;
0043 FMSZPG = $0043 ;TOTAL OF 7 BYTES FOR DISK FILE MANAGER ZERO PAGE
;
;
004A CKEY = $004A ;FLAG SET WHEN GAME START PRESSED
004B CASSBT = $0048 ;CASSETTE BOOT FLAG
004C DSTAT = $004C ;DISPLAY STATUS
;
004D ATRACT = $004D ;ATRACT FLAG
004E DRKMSK = $004E ;DARK ATRACT FLAG
004F COLRSH = $004F ;ATRACT COLOR SHIFTER (EOR'D WITH PLAYFIELD COLORS)
;
;LEDGE = 2 ;LMARGN'S VALUE AT COLD START
;REDGE = 39 ;
0050 TMPCHR = $0050
0051 HOLD1 = $0051
0052 LMARGN = $0052 ;LEFT MARGIN (SET TO ONE AT POWER ON)
0053 RMARGN = $0053 ;RIGHT MARGIN (SET TO ONE AT POWER ON)
0054 ROWCRS = $0054 ;CURSOR COUNTERS
0055 COLCRS = $0055
0057 DINDEX = $0057
0058 SAVMSC = $0056
005A OLDROW = $005A
005B OLDCOL = $005B
005D OLDCHR = $005D ;DATA UNDER CURSOR
005E OLDADR = $005E
0060 NEWROW = $0060 ;POINT DRAW GOES TO
0061 NEWCOL = $0061
0063 LOGCOL = $0063 ;POINTS AT COLUMN IN LOGICAL LINE
0004 AORESS = $0064
0066 MLTTMP = $0066
0068 SAVADR = $0068
006A RAMTOP = $006A ;RAM SIZE DEFINED BY POWER ON LOGIC
006B BUFCNT = $006B ;BUFFER COUNT
006C BUFSTR = $006C ;EDITOR GETCH POINTER
006E BITMSK = $006E ;BIT MASK
; LOTS OF RANDOM TEMPS
007B SWPFLG = $007B ;NON-0 IF TXT AND REGULAR RAM IS SWAPPED
007C HOLDCH = $007C ;CH IS MOVED HERE IF KGETCH BEfore CNTL & SHIFT PROC
;
;
;
; 80 - FF ARE FOR FP, USER, FMS AND DOS
;
;
; PAGE 1 -- STACK
;
;
; PAGE TWO RAM ASSIGNMENTS
;
0200 INTABS = $0200 ;INTERRUPT RAM
0200 VDBLST = $0200 ;DISPLAY LIST NMI VECTOR
0202 VPRCED = $0202 ;PROCEED LINE IRQ VECTOR
0204 VINTER = $0204 ;INTERRUPT LINE IRQ VECTOR
0206 VBREAK = $0206 ;SOFTWARE BREAK (00) INSTRUCTION IRQ VECTOR
0208 VKEYBD = $0208 ;POKEY KEYBOARD IRQ VECTOR
020A VSERIN = $020A ;POKEY SERIAL INPUT READY IRQ
020C VSEROR = $020C ;POKEY SERIAL OUTPUT READY IRQ
020E VSEROC = $020E ;POKEY SERIAL OUTPUT COMPLETE IRQ
0210 VTIMR1 = $0210 ;POKEY TIMER 1 IRQ
0212 VTIMR2 = $0212 ;POKEY TIMER 2 IRQ
0214 VTIMR4 = $0214 ;POKEY TIMER 4 IRQ
0216 VIMIRQ = $0216 ;IMMEDIATE IRQ VECTOR
0218 CDTMV1 = $0218 ;COUNT DOWN TIMER 1
021A CDTMV2 = $021A ;COUNT DOWN TIMER 2
021C CDTMV3 = $021C ;COUNT DOWN TIMER 3
021E CDTMV4 = $021E ;COUNT DOWN TIMER 4
0220 CDTMV6 = $0220 ;COUNT DOWN TIMER 5
0222 VVBLKI = $0222 ;IMMEDIATE VERTICAL BLANK NMI VECTOR
0224 VVBLKD = $0224 ;DEFERRED VERTICAL BLANK NMI VECTOR
0226 CDTMA1 = $0226 ;COUNT DOWN TIMER 1 JSR ADDRESS
0228 CDTMA2 = $0228 ;COUNT DOWN TIMER 2 JSR ADDRESS
022A CDTMF3 = $022A ;COUNT DOWN TIMER 3 FLAG
022B SRTIMR = $022B ;SOFTWARE REPEAT TIMER
022C CDTMF4 = $022C ;COUNT DOWN TIMER 4 FLAG
022E CDTMF5 = $022E ;COUNT DOWN TIMER 5 FLAG
022F SDMCTL = $022F ;SAVE DMACTL REGISTER
0230 SDLSTL = $0230 ;SAVE DISPLAY LIST LOW BYTE
0231 SDLSTH = $0231 ;SAVE DISPLAY LIST HIGH BYTE
0232 SSKCTL = $0232 ;SKCTL REGISTER RAM
;
0234 LPENH = $0234 ;LIGHT PEN HORIZONTAL VALUE
0235 LPENV = $0235 ;LIGHT PEN VERTICAL VALUE
026F GPRIOR = $26F ;Global priority call
;
;
; POTENTIOMETERS
;
;
0270 PADDL0 = $0270
0271 PADDL1 = $0271
0272 PADDL2 = $0272
0273 PADDL3 = $0273
0274 PADDL4 = $0274
0275 PADDL5 = $0275
0276 PADDL6 = $0276
0277 PADDL7 = $0277
;
;
; JOYSTICKS
;
;
0278 STICK0 = $0278
0279 STICK1 = $0279
027A STICK2 = $027A
027B STICK3 = $027B
;
;
; PADDLE TRIGGER
;
;
027C PTRIG0 = $027C
027D PTRIG1 = $027D
027E PTR1G2 = $027E
027F PTRIG3 = $027F
0280 PTRIG4 = $0280
0281 PTRIG5 = $0281
0282 PTRIG6 = $0282
0283 PTRIG7 = $0283
;
;
; JOYSTICK TRIGGER
;
;
0284 STRIG0 = $0284
0285 STRIG1 = $0285
0286 STRIG2 = $0286
0287 STRIG3 = $0287
;
; Many random OS variables, the following were commented
;
0290 TXTROW = $0290 ;Text rowcrs
0291 TXTCOL = $0291 ;Text colcrs
0293 TINDEX = $0293 ;text index
0294 TXTMSC = $0294 ;fools convert into new msc
0296 TXTOLD = $0296 ;oldrow and oldcol for text (etc.)
02A2 ESCFLG = $02A2 ;Escape flag
02B2 LOGMAP = $02B2 ;Logical line start bit map
02B6 INVFLAG = $02B6 ;Inverse video flag (toggled by Atari key)
02B7 FILFLG = $02B7 ;Fill flag for draw
02B6 SCRFLG = $02B8 ;Set if scroll occures
02BE SHFLOK = $02BE ;Shift lock
02BF BOTSCR = $02BF ;Bottom of screen: 24 Norm. 4 Split.
;
;
; COLORS
;
;
02C0 PCOLR0 = $02C0 ;P0 COLOR
02C1 PCOLR1 = $02C1 ;P1 COLOR
02C2 PCOLR2 = $02C2 ;P2 COLOR
02C3 PCOLR3 = $02C3 ;P3 COLOR
02C4 COLOR0 = $02C4 ;COLOR 0
02C5 COLOR1 = $02C5 ;COLOR 1
02C6 COLOR2 = $02C6 ;COLOR 2
02C7 COLOR3 = $02C7 ;COLOR 3
02C6 COLOR4 = $02C8 ;COLOR 4
;
;
; GLOBAL VARIABLES
;
;
02E4 RAMSIZ = $02E4 ;RAM SIZE (HI BYTE ONLY)
02E5 MEMIOP = $0215 ;TOP OF AVAILABLE USER MEMORY
02E7 MEMLO = $02E7 ;BOTTOM OF AVAILABLE USER MEMORY
02EA DVSTAT = $02EA ;STATUS BUFFER
;
02F0 CRSINH = $02F0 ;CURSOR INHIBIT (00 = CURSOR ON)
02F1 KEYDEL = $02F1 ;Key delay
02F3 CHACT = $02F3 ;CHACTL REGISTER RAM
02F4 CHBAS = $02F4 ;CHBAS REGISTER RAM
02FD FILDAT = $02FD ;RIGHT FILL DATA (DRAW)
02FB ATACHR = $02FB ;Atascii character
02FC CM = $02FC ;global variable for keyboard
02FE DSPFLA = $02FE ;DISPLAY FLAG: DISPLAYS CNTLS IF NON ZERO:
02FF SSFLAG = $02FF ;Start/stop flag for paging (CNTL 1). Cleared by Break
;
; Page three RAM assignments
;
; Device control blocks
; (SIO)
0300 DCB = $0300 ;Device control block
0300 DDEVIC = $0300 ;Peripheral Unit 1 bus I.D. number
0301 DUNIT = $0301 ;Unit number
0302 DCOMND = $0302 ;Bus command
0303 DSFATS = $0303 ;Command Type/status return
0304 DBUFLO = $0304 ;Data buff- points low
0305 DBUFHI = $0305
0306 DTIMLO = $0306 ;Device time out in 1 second units
0308 DBYTLO = $0308 ;Number of bytes to be transvered low byte
0309 DBYTHI = $0309
030A DAUX1 = $030A ;Command Aux byte 1
0308 DAUX2 = $0308
;
0340 IOCB = $0340
0340 ICHID = $0340 ;Handler index number (FF = IOCB free)
0341 ICDNO = $0341 ;Device number (drive number)
0342 ICCOM = $0342 ;Command code
0343 ICSTA = $0343 ;Status of last IOCB action
0344 ICBAL = $0344 ;Buffer address low byte
0345 ICBAH = $0345
0346 ICPTL = $0346 ;Put byte routine address - 1
0347 ICPTH = $0347
0348 ICBLL = $0348 ;Buffer length low byte
0349 ICBLH = $0349
034A ICAX1 = $034A ;Auxiliary information first byte
0348 ICAX2 = $034B
034C ICSPR = $034C ;four spare bytes
;
03C0 PRNBUF = $0300 ;Printer buffer (40 bytes)
; (21 spare bytes)
;
; Page Four Ram Assignnents
03FD CASBUF = $03FD ;Cassette Buffer (131 bytes)
;
0480 USAREA = $0480 ; (0480 thru 05FF for the user)
; (except for floating point...)
;
; FLOATING POINT ROM ROUTINES
;
;
; IF CARRY IS USED THEN CARRY CLEAR => NO ERROR. CARRY SET => ERROR
;
D800 AFP = $D800 ;ASCII -> FLOATING POINT (FP)
; INBUFF * CIX -> FR0, CIX, CARRY
D8E6 FASC = $D8E6 ;FP -> ASCII FR0 -> F0R,FD0-1, CARRY
D9AA IFP = $D9AA ;INTEGER -> FP
; 0-$FFFF (LSB, MSB) IN FR0,FR0+1->FR0
D92D FPI = $D92D ;FP -> INTEGER FR0 -> FR0,FR0+1, CARRY
DA60 FSUB = $DA60 ;FR0 <- FR0 - FR1, CARRY
DA66 FADD = $DA66 ;FR0 <- FR0 + FR1 ,CARRY
DADB FMUL = $DADB ;FR0 <- FR0 * FR1 ,CARRY
DB28 FDIV = $DB28 ;FR0 <- FR0 / FR1 ,CARRY
DD89 FLD0R = $DD89 ;FLOATING LOAD REG0 FR0 <- (X,Y)
DD80 FLD0P = $DD8D ; FR0 <- (FLPTR)
DD98 FLD1R = $DD9B ; FR1 <- (X,Y)
DD9C FLD1P = $DD9C ; FR1 <- (FLPTR)
DDA7 FST0R = $DDA7 ;FLOATING STORE REG0 (X,Y) <- FR0
DDAB FST0P = $DDAB ; (FLTPTR)<- FR0
DDB6 FMOVE = $DDB6 ;FR1 <- FR0
DD40 PLYEVL = $DD40 ;FR0 <- P(Z) = SUM(I = N TO 0) (A(I) *Z**I) CARRY
; INPUT: (X,Y) = A(N), A(N-I)...A(0) -> PLYARG
; ACC = # OF COEFFICIENTS = DEGREE + 1
; FR0 = Z
DDC0 EXP = $DDC0 ;FR0 <- E**FR0 = EXP10(FR0 * LOG10(E)) CARRY
DDCC EXP10 = $DDCC ;FR0 <- 10**FR0 CARRY
DECD LOG = $DECD ;FR0 <- LN(FR0) = LOG10(FR0) / LOG10(E) CARRY
DE01 LOG10 = $DE01 ;FR0 <- LOG10(FR0) CARRY
;
;
; THE FOLLOWING ARE IN THE BASIC CARTRIDGE:
;
;
BD81 SIN = $BD81 ;FR0 <- SIN(FR0) DEGFLG=0 => RADS, 6->DEG. CARRY
BD73 COS = $BD73 ;FR0 <- COS(FR0) CARRY
BD43 ATAN = $BD43 ;FR0 <- ATN(FR0) CARRY
BEB1 SQR = $BEB1 ;FR0 <- SQUAREROOT(FR0) CARRY
;
;
; FLOATING POINT ROUTINES ZERO PAGE (NEEDED ONLY IF F.P.
; ROUTINES ARE CALLED)
00D4 FR0 = $00D4 ;FP REG0
00E0 FR1 = $00E0 ;FP REG1
00F2 CIX = $00F2 ;CURRENT INPUT INDEX
00F3 INBUFF = $00F3 ;POINTS TO USER'S LINE INPUT BUFFER
00FB RADFLG = $00FB ;0 = RADIANS, 6 = DEGREES
00FC FLTPTR = $00FC ;POINTS TO USERS FLOATING POINT NUMBER
;
;
; FLOATING POINT ROUTINES' NON-ZP RAM
;
; (057E to 06FF)
;
0580 LBUFF = $0580 ;LINE BUFFER
05E0 PLYARG = LBUFF+$60 ;POLYNOMILA ARGUMENTS
;
;
;
;
;
; COLLEEN MNEMONICS
;
;
;
D200 POKEY = $D200 ;VBLANK ACTION: DESCRIPTION:
D200 POT0 = POKEY+0 ;POT0-->PADDL0 0-227 IN RAM CELL
D201 POT1 = POKEY+1 ;POT1-->PADDL1 0-227 IN RAM CELL
D202 POT2 = POKEY+2 ;POT2-->PADDL2 0-227 IN RAM CELL
D203 POT3 = POKEY+3 ;POT3-->PADDL3 0-227 IN RAM CELL
D204 POT4 = POKEY+4 ;POT4-->PADDL4 0-227 IN RAM CELL
D205 POTS = POKEY+5 ;POT5-->PADDL5 0-227 IN RAM CELL
D206 POTC = POKEY+6 ;POT6-->PADDL8 0-227 IN RAM CELL
D207 POT7 = POKEY+7 ;POT7-->PADDL7 0-227 IN RAM CELL
D208 ALLPOT = POKEY+8 ;???
D209 KBCODE = POKEY+9
D20A RANDOM = POKEY+10
D20B POTGO = POKEY+11 ;Strobed
; n/a
D20D SERIN = POKEY+13
D20E IRQST = POKEY+14
D20F SKSTAT = POKEY+15
;
D200 AUDF1 = POKEY+0
D201 AUDC1 = POKEY+1
D202 AUDF2 = POKEY+2
D203 AUDC2 = POKEY+3
D204 AUDF3 = POKEY+4
D205 AUDC3 = POKEY+5
D206 AUDF4 = POKEY+6
D207 AUDC4 = POKEY+7
D208 AUDCT = POKEY+8 ;NONE AUDCTL<--[SIO]
D209 STIMER = POKEY+9
D20A SKRES = POKEY+10 ;NONE SKRES<--[SIO]
;
D20B POTGO = POKEY+11
D20D SEROUT = POKEY+13 ;NONE SEROUT<--[SIO]
D20E IRQEN = POKEY+14 ;POKMSK-->IRQEN (AFFECTED BY OPEN S: OR E:)
D20F SKCTL = POKEY+16 ;SSKCTL-->SKCTL SSKCTL<--[SIO]
;
D000 CTIA = $D000
D000 HPOSP0 = CTIA+0
D001 HPOSP1 = CTIA+1
D002 HPOSP2 = CTIA+2
D003 HPOSP3 = CTIA+3
D004 HPOSM0 = CTIA+4
D005 HPOSM1 = CTIA+5
D006 HPOSM2 = CTIA+6
D007 HPOSM3 = CTIA+7
D008 SIZEP0 = CTIA+8
D009 SIZEP1 = CTIA+9
D00A SIZEP2 = CTIA+10
D00B SIZCP3 = CTIA+11
D00C SIZEM = CTIA+12
D00D GRAFP0 = CTIA+13
D00E GRAFP1 = CTIA+14
D00F GRAFP2 = CTIA+15
D010 GRAFP3 = CTIA+16
D011 GRAFM = CTIA+17
D012 COLPM0 = CTIA+18 ;PCOLR0-->COLPM0 WITH ATTRACT MODE
D013 COLPM1 = CTIA+19 ;ETC.N
D014 COLPM2 = CTIA+20
D015 COLPM3 = CTIA+21
D016 COLPF0 = CTIA+22
D017 COLPF1 = CTIA+23
D018 COLPF2 = CTIA+24
D019 COLPF3 = CTIA+25
D01A COLBK = CTIA+26
D01B PRIOR = CTIA+27
D01C VDELAY = CTIA+28
D01D GRACTL = CTIA+29
D01E HITCLR = CTIA+30
D01F CONSOL = CTIA+31 ;$08-->CONSOL TURN OFF SPEAKER
;
D000 M0PF = CTIA+0
D002 M2PF = CTIA+2
D003 M3PF = CTIA+3
D004 P0PF = CTIA+4
D005 P1PF = CTIA+5
D006 P2PF = CTIA+6
D007 P3PF = CTIA+7
D008 M0PL = CTIA+8
D009 M1PL = CTIA+9
D00A M2PL = CTIA+10
D00B M3PL = CTIA+11
D00C P0PL = CTIA+12
D00D P1PL = CTIA+13
D00E P2PL = CTIA+14
D00F P3PL = CTIA+15
D010 TRIG0 = CTIA+16 ;TRIG0-->STRIG1
D011 TRIG1 = CTIA+17 ;ETC.
D012 TR1G2 = CTIA+18
D013 TRIG3 = CTIA+19
D014 PAL = CTIA+20
;
D400 ANTIC = $D400
D400 DMACTL = ANTIC+0 ;DMACTL<--SDMCTL ON OPEN S: OR E:
D401 CHARCTL = ANTIC+1 ;CHACTL<--CHACT ON OPEN S: OR E:
D402 DLISTL = ANTIC+2 ;DIISTt<--SDLSTL ON OPEN S: OR E:
D403 DLISTH = ANTIC+3 ;OLISFH<--SDLSTH ON OPEN S: OR E:
D404 HSCROL = ANTIC+4
D405 VSCROL = ANTIC+5
D407 PMBASE = ANTIC+7
D409 CHBASE = ANTIC+9 ;CMBASE<--CHBAS ON OPEN S: OR E:
D40A WSYNC = ANTIC+10
D408 VCOUNT = ANTIC+11
D40C PENH = ANTIC+12
D40D PENV = ANTIC+13
D40E NMIEN = ANTIC+14 ;NMIEN<--40 POWER ON AND [SETVBV]
D40F NMIRES = ANTIC+15 ;STROBED
D40F HMIST = ANTIC+15
;
; Lots and lots of unofficial
; Mnemonics for display list instructions.
; as well as other bit patterns.
;
; DL prefix implies display list
; instruction, naturally
;
0000 DLBL1 = 0 ; One blank line
0010 DLBL2 = $10 ; Two blank lines
0020 DLBL3 = $20 ; Three
0030 DLBL4 = $30 ; Four
0040 DLBL5 = $40 ; Five
0050 DLBL6 = $50 ; Six
0060 DLBL7 = $60 ; Seven
0070 DLBL8 = $70 ; Eight blank lines
0080 DLINT = $80 ; Generate DisplayListInterrupt when this
; instruction is interpreted.
0001 DLJMP = $1 ; Tells Antic Chip to junp to contents of next two bytes
0041 DLJVB = $41 ; Same as DLJMP but also halts ANTIC 'till next verticle blank
0040 DLLDM = $40 ; Tells Antic chip to start retrieving data from memory referenced by the next t
0020 DLVSCR = $20 ; (sort of) enables vertical scroll
0010 DLHSCR = $10 ; enable horizontal scroll
;
; Playfield Instructions
;
000F DLPF15 = 15 ; 320 dots 2 colors 1 scan line
000E DLPF14 = 14 ; 160 4 1
000D DLPF13 = 13 ; 160 4 2
000C DLPF12 = 12 ; 160 2 1
000B DLPF11 = 11 ; 160 2 2
000A DLPF10 = 10 ; 80 4 4
0009 DLPF9 = 9 ; 80 2 4
0008 DLPF8 = 8 ; 40 4 8
; Character PF types
0007 DLPF7 = 7 ; 20 chars 5 colors 16 scan lines
0006 DLPF6 = 6 ; 20 5 8
0005 DLPF5 = 5 ; 40 5 16 (hairy 4 color characters)
0004 DLPF4 = 4 ; 40 5 8
0003 DLPF3 = 3 ; 40 2 10 (Text processing)
0002 DLPF2 = 2 ; 40 2 8 (Normal text mode)
; PF1 & PF0 are special. . . .
;
; Player & Missile Offsets
; Denoted by PM prefix
;
0024 PMLF = $24 ;left side of screen
00DD PMRF = $DD ;flight side of screen
0180 PMDM = $180 ;Missile offset, for double line resolution
0200 PMDP0 = $200 ;Player 0
0280 PMDP1 = $280 ;Player 1
0300 PMDP2 = $300 ;Player 2
0380 PMDP3 = $380 ;Player 3
0300 PMSM = 2*PMDM ;Missile offset for single line resolution
0400 PMSP0 = 2*PMDP0 ;Player 0
0500 PMSP1 = 2*PMDP1 ; 1
0600 PMSP2 = 2*PMDP2 ; 2
0700 PMSP3 = 2*PMDP3 ; 3
;
; Colors. denoted by CL
;
0000 CLGREY = 0 ;grey
0010 CLGOLD = $10 ;gold
0020 CLORNG = $20 ;orange
0030 CLRED = $30 ;red-orange
0040 CLPINK = $40 ;pink
0050 CLPURP = $50 ;purple
0060 CLPURB = $60 ;purple blue
0070 CLPBLU = $70 ;blue 1
0080 CLBLUE = $80 ;blue 2
0090 CLLBLU = $90 ;light blue
00A0 CLTURQ = $A0 ;turquoise
00B0 CLGBLU = $B0 ;green blue
00C0 CLGREN = $C0 ;green
0000 CLYGRN = $D0 ;yellow green
00E0 CLOGRN = $E0 ;orange green
00F0 CLLTOR = $F0 ;light orange
; Bit Masks for console switches
;
0001 SWSTRT = $1 ;Start
0002 SWSEL = $2 ;Select
0004 SWOPT = $4 ;Option
; Joystick bit masks
0008 JYR = 8 ;Right
0004 JYL = 4 ;Left
0002 JYB = 2 ;Back
0001 JYF = 1 ;Forward
D300 PIA = $D300
D300 PORTA = PIA+0 ;PORTA-->STICK0,1 X-Y CONTROLLERS
D301 PORTB = PIA+1 ;PORTB-->STICK2,3
D302 PACTL = PIA+2 ;NONE PACTL<--3C [INIT]
D303 PBCTL = PIA+3 ;NONE PBCTL<--3C [INIT]
0030 ASCZER = '0 ;Ascii zero
003A COLON = $3A ;Ascii Colon
009B EOL = $9B ;End of Record
; The Following are subroutines
F385 PUTLIN = $F385 ;X -- Lo byte
;Y -- Hi byte
;of line
E7D1 XVB = $E7D1 ;System VBLANK exit routine
;
;
;
; End of Atari equates.
;
; The rest of this is (C)1981 John H. Palevich
;
;
1000 ORG = $1000 ;Must be at least 3K of memory
;above this point. . . .
1000 .=ORG
;Once in the actual game you can make
;identical copies of it by pressing OPTION
;and SELECT down simultaneously between
;plays. The Atari will beep twice and you
;should press play & record and then RETURN
;to make a copy. After one copy is made
;the game starts all over again.
1000 PST=.
;
; This is the Boot tape header table.
;
1000 00 .BYTE 0 ;Traditional
1001 09 .BYTE PND-PST+127/128 ;# of 128 byte blocks in program
1002 00 10 .ADDR PST ;Start of place to load program
1004 08 10 .ADDR PINIT ;Place to jump after loading
;program
; ENTRY POINT FOR MULTI-STAGE BOOT PROCESS.
1006 18 CLC
1007 60 RTS
; ENTRY POINT FOR FIRST TIME INITIALIZATION
1008 A9 3C PINIT: LDA #$3C
100A 8D 02 D3 STA PACTL ;turn off cassete motor
100D A9 16 LDA #RESTRT&$FF ;Shove the restrt vector into
100F 85 0A STA DOSVEC ;the DOS vector.
1011 A9 10 LDA #RESTRT^
1013 85 0B STA DOSVEC+1
1015 60 RTS
; WARMSTART ENTRY POINT
;
1016 4C 4E 12 RESTRT: JMP BEGIN
;
;
; .....................
; Look, up in the sky! Its a helicopter, it's a plane. It's
; a saucer, no, it's Jack's wonderful 'SHOOT' game.
;
; Zero-Page-Variables
;(None of these variables Have to be on the zero page, but
;putting them here speeds up and shortens the code)
;
00B0 DLIC = $B0 ;Counter of display list interrupts
00B1 DSCOR = $B1 ;Delta score.
00B2 MX = $B2 ;Missile X coordinate
00B3 MDX = $B3 ;Missile X velocity
00B4 MY = $B4 ;Missile Y position (Zero means no missile
;on the screen.)
00B5 DSEC = $B5 ;mod 15 counter for score to second conversion
00B6 JIFF = $B6 ;mod 60 counter for jiffy to second conversion
00B7 STOP = $B7 ;Non zero neans ignore player's button. Used
;to keep him from firing unless we want him to.
;
; Data Tables
;
; MDLIST -- My display list. Consists of the standard-24-blank-scan-lines.
; 8 scan lines of text (the score and copyright line)
; 11 sets of 16 scan lines with a display list interrupt
; occuring at the start of each pair
; and a final jump & wait for vertical blank instruction
;
1019 70 70 70 MDLIST: .BYTE DLBL8,DLBL8,DLBL8
101C 46 .BYTE DLLDM+DLPF6 ;C
101D 00 18 .ADDR SCORLN
101F F0 70 .BYTE DLBL8+DLINT,DLBL8 ;1,2
1021 F0 70 .BYTE DLBL8+DLINT,DLBL8 ;3,4
1023 F0 70 .BYTE DLBL8+DLINT,DLBL8 ;5,6
1025 F0 70 .BYTE DLBL8+DLINT,DLBL8 ;7,8
1027 F0 70 .BYTE DLBL8+DLINT,DLBL8 ;9,10
1029 F0 70 .BYTE DLBL8+DLINT,DLBL8 ;11,12
102B F0 70 .BYTE DLBL8+DLINT,DLBL8 ;13,14
102D F0 70 .BYTE DLBL8+DLINT,DLBL8 ;15,16
102F F0 70 .BYTE DLBL8+DLINT,DLBL8 ;17,18
1031 F0 70 .BYTE DLBL8+DLINT,DLBL8 ;19,20
1033 F0 70 .BYTE DLBL8+DLINT,DLBL8 ;21,22
1035 41 .BYTE DLJVB
1036 19 10 .ADDR MDLIST
;
; Message table
;
1038 28 43 29 TMSG: .ASCII "(C)1981 J H PALEVICH" ;Horrible bugs will infest the code
103B 31 39 38
103E 31 20 4A
1041 20 48 20
1044 50 41 4C
1047 45 56 49
104A 43 48
;of who-so-ever changes this copyright
;message to something else!
;
; The next many tables are for the display list interrupt handler.
; They are all 11 bytes long, so that there is one byte in each
; table for each display list interrupt. The First DLI uses the
; rirst byte in the table, and so forth, so in the TCOLB table,
; for instance, the top of the sky is black, then the first DLI
; makes it turn CLBLUE, the second CLLBLU. and so on.
;
;
; TCOLB - table of colors for backround
; The sky starts out black and turns light blue, then
; the backround turns green for the 'ground' under the gun.
;
104C 80 90 82 TCOLB: .BYTE CLBLUE,CLLBLU,CLBLUE+2
104F 92 84 94 .BYTE CLLBLU+2,CLBLUE+4,CLLBLU+4
1052 86 96 88 .BYTE CLBLUE+6,CLLBLU+6,CLBLUE+8
1055 98 C8 .BYTE CLLBLU+8,CLGREN+8
;
; TCOLP - COLOR PLAYER ZERO
; Player zero is the planes in the sky and the gun on the ground
;
1057 08 18 TCOLP: .BYTE CLGREY+8,CLGOLD+8
1059 28 38 .BYTE CLORNG+8,CLRED+8
105B 48 58 .BYTE CLPINK+8,CLPURP+8
105D 68 78 .BYTE CLPURB+8,CLPBLU+8
105F 80 38 38 .BYTE CLBLUE,CLRED+8,CLRED+8
;
; TPX -- Players X position
; The gun it always stuck at 124.
; DPLANE takes care of the planes' x position.
; DLIH sets the X position to zero to kill the
; plane and get it off the screen.
;
1062 00 01 02 TPX: .BYTE 0,1,2,3,4,5,6,7,8,124,124
1065 03 04 05
1068 06 07 08
106B 7C 7C
;
; TDX -- Player's velocity.
; The gun is always zero, so it will not drift off
; to either side.
;
106D 01 02 03 TDX: .BYTE 1,2,3,2,1,255,254,253
1070 02 01 FF
1073 FE FD
1075 FE 00 00 .BYTE 254,0,0
;
; TVAL -- PLAYER'S POINT-VALUE
;
; Set by DPLANE
; Used by DLIH
;
1078 01 02 03 TVAL: .BYTE 1,2,3,4,5,6,7,8,9,10,11
107B 04 05 06
107E 07 08 09
1081 0A 0B
;
; TWID -- width of the player
;
; 0 -- normal (two GR. 0 characters) wide
; 1 -- double (four Gr. 0 characters) wide
; The gun is double width
;
1083 00 01 00 TWID: .BYTE 0,1,0,1,0,1,0,1,0,1,1
1086 01 00 01
1089 00 01 00
108C 01 01
;
; That's the end of the tables used by the DLIH
; routine.
;
;
; JTAB -- missiles X velocity
; Used to convert from the joystick direction to
; the speed end direction of the missile. Used by VBLI.
;
108E 00 01 FF JTAB: .BYTE 0,1,255,0
1091 00
;
; GUNTAB -- Picture of gun in all three
; directions.
;
;........
;......++
;.....++.
;....++..
;...+++..
;..++++..
;.++++++.
;++++++++
1092 00 03 06 GUNTAB: .BYTE 0,3,6,$C,$1C,$3C,$7E,$FF
1095 0C 1C 3C
1098 7E FF
;........
;++......
;.++.....
;..++....
;..+++...
;..++++..
;.++++++.
;++++++++
109A 00 C0 60 .BYTE 0,$C0,$60,$30,$38,$3C,$7E,$FF
109D 30 38 3C
10A0 7E FF
;........
;...++...
;...++...
;...++...
;.. ++...
;..++++..
;.++++++.
;++++++++
10A2 00 18 18 .BYTE 0,$18,$18,$18,$18,$3C,$7E,$FF
10A5 18 18 3C
10A8 7E FF
; Pattern defn's.
;
; Used by DPLANE to draw the planes. Note that
; the top two lines must be blank or else all sorts
; of messy chopping effects will occur.
;
;
; Pattern Zero is a helicopter flying left.
;
;........
;........
;+++++...
;..+.....
;++++..+.
;+..++++.
;+..+....
;++++....
10AA 00 00 F8 PTOL: .BYTE 0,0,$F8,$20,$F2,$9E,$90,$F0
10AD 20 F2 9E
10B0 90 F0
;........ helicopter flying right.
;........
;...+++++
;.....+..
;.+..++++
;.++++..+
;....+..+
;....++++
10B2 00 00 1F .BYTE 0,0,$1F,4,$4F,$79,9,$F
10B5 04 4F 79
10B8 09 0F
;........ airplane flying left.
;........
;.......+
;....++.+
;..++++++
;.+++++++
;...++...
;........
10BA 00 00 01 .BYTE 0,0,1,$0D,$3F,$7F,$18,0
10BD 0D 3F 7F
10C0 18 00
;........ airplane flying right
;........
;+.......
;+.++....
;++++++..
;+++++++.
;...++...
;........
10C2 00 00 80 .BYTE 0,0,$80,$B0,$FC,$FE,$18,0
10C5 B0 FC FE
10C8 18 00
;........ saucer flying left, right, hovering, etc.
;...++...
;..+..+..
;.++++++.
;+......+
;.++++++.
;........
;........
10CA 00 18 24 .BYTE 0,$18,$24,$7E,$81,$7E,0,0
10CD 7E 81 7E
10D0 00 00
;
; TPLANE DX, VAL, WID, PAT table
;
; TPLANE is a table used by DPLANE to
; create planes. What DPLANE does Is pick a random number
; between zero and five and use that nunber to fill in the
; IDX, FVAL, TWID and player zero slots for that kind of plane.
;
; There is no real reason to stop with only six
; kinds of planes. . . .
;
10D2 01 05 00 TPLANE: .BYTE 1,5,0,8 ;Helicopter, left
10D5 08
10D6 FF 05 00 .BYTE $FF,5,0,0 ; " " , right
10D9 00
10DA 02 0A 01 .BYTE 2,10,1,24 ;Airplane, left
10DD 18
10DE FE 0A 01 .BYTE $FE,10,1,16 ; " " , right
10E1 10
10E2 03 19 00 .BYTE 3,25,0,32 ;Saucer, left
10E5 20
10E6 FD 19 00 .BYTE $FD,25,0,32 ;Saucer, right
10E9 20
; Player missile table equates
;
1800 MPMBAS = ORG+$800 ;Player missile base --
;Leave 2K for the main program
1800 SCORLN = MPMBAS ;Score line (uses 20 bytes)
0080 GUNOFF = 96 ;Gun offset -- Y position of top
;of gun.
1A80 GUNPOS = MPMBAS+PMDP0+GUNOFF ;Memory location of
;top of gun in player0 memory.
1800 SCORE = SCORLN ;Address of Score (six digets)
1807 HISCOR = SCORLN+7 ;Address of High score (six digets)
180E TIME = SCORLN+14 ;Address of Time remaining (six digets)
;
;
; This is the DLI handler --
; it is called every time the Antic chip fetches a display
; list byte with the high bit set. It saves the A and X registers.
; changes the sky & color & width & position of the next plane,
; and checks to see if the previous plane has been hit. If so, it
; moves that plane off the screen and adds the point value of that
; plane to the DSCOR variable. Then it restores X & A and returns.
;
;
10EA 48 DLIH: PHA ;Save A
10EB 8A TXA
10EC 48 PHA ;Save X
10ED A6 B0 LDX DLIC ;Change the sky's color as fast as
10EF E8 INX ;we can.
10F0 BD 4C 10 LDA TCOLB,X ;but.
10F3 8D 0A D4 STA WSYNC ;wait untill we can do it without
10F6 8D 1A D0 STA COLBK ;the user noticing it.
10F9 A6 B0 LDX DLIC
10FB AD 08 D0 LDA M0PL ;Did missile 0 hit anything?
10FE 29 01 AND #1 ;like P0?
1100 F0 13 BEQ DLIH2 ;No.
1102 A9 00 LDA #0 ;Yes:
1104 9D 62 10 STA TPX,X ;So zero x position.
1107 9D 6D 10 STA TDX,X ;and x velocity.
110A BD 78 10 LDA TVAL,X ;and add the value of
110D 18 CLC ;that player to DSCOR
110E 65 B1 ADC DSCOR
1110 85 B1 STA DSCOR
1112 8D 1E D0 STA HITCLR ;And clear the hit registers.
1115 E8 DLIH2: INX ;In any event, update:
1116 86 B0 STX DLIC
1118 BD 62 10 LDA TPX,X ;plane's X position.
111B 18 CLC
111C 7D 6D 10 ADC TDX,X
111F 9D 62 10 STA TPX,X
1122 8D 00 D0 STA HPOSP0
1125 BD 57 10 LDA TCOLP,X ;plane's color
1128 8D 12 D0 STA COLPM0
112B BD 83 10 LDA TWID,X ;plane's width
112E 8D 08 D0 STA SIZEP0
1131 68 PLA ;restore X
1132 AA TAX
1133 68 PLA ;restore A
1134 40 RTI ;and return.
;
; VBLH -- vertical blank interrupt
; gets called 60 times a second when the TV gun has just
; retraced the screen and the Antic chip is starting to read the
; display list all over again.
;
; It updates the player's score & time-left counter,
; updates the missile if it is in flight, fires it if it is not
; in flight and if the joystick's button is pressed, resets the
; counter that the display list interrupt handler uses to tell
; where it is, and kills the missile if it hit a plane or went
; off the top of the screen.
;
1135 A5 B1 VBLH: LDA DSCOR ;Check if there are any unscored
1137 D0 08 BNE VBL5 ;points left. Yes.
1139 A9 80 LDA #$80 ;No.
113B 8D 03 D2 STA AUDC2 ;Turn off point sound
113E 4C 90 11 JMP VBL7
1141 38 VBL5: SEC ;Subtract one from the unscored
1142 E9 01 SBC #1 ;points counter.
1144 85 B1 STA DSCOR
1146 A9 8A LDA #$8A ;Turn on the point sound.
1148 8D 03 D2 STA AUDC2
114B A2 05 LDX #5 ;Add one to the SCORE counter.
114D BD 00 18 VBL6: LDA SCORE,X ;Which by an amazing coincidence
1150 18 CLC ;is in a human readable forn.
1151 69 01 ADC #1
1153 09 10 ORA #$10 ;If it was a space make it a '1'.
1155 9D 00 18 STA SCORE,X
1158 C9 1A CMP #$1A ;Greater than a '9'?
115A D0 09 BNE VBLH5 ;No.
115C A9 10 LDA #$10 ;Yes. Set to '0' ind add one to
115E 9D 00 18 STA SCORE,X ;the next most significant diget.
1161 CA DEX
1162 4C 4D 11 JMP VBL6
1165 A5 B7 VBLH5: LDA STOP ;No free time if
1167 D0 27 BNE VBL7 ;we're STOPed.
1169 A6 B5 LDX DSEC ;Has he scored 15 points in a row
116B E8 INX ;yet?
116C 86 B5 STX DSEC
116E E0 0F CPX #15
1170 D0 1E BNE VBL7 ;Nope.
1172 A2 00 LDX #0 ;Yes. Reset this counter, then, and
1174 86 B5 STX DSEC
1176 A2 05 LDX #5 ;give this man a second of free time.
1178 BD 0E 18 VBL8: LDA TIME,X ;(this routine is just like the VBL6
117B 18 CLC ;one, only it fiddles with numbers that
117C 69 01 ADC #1 ;are a different color. . . .)
117E 09 90 ORA #$90
1180 9D 0E 18 STA TIME,X
1183 C9 9A CMP #$9A
1185 90 09 BCC VBL7
1187 A9 90 LDA #$90
1189 9D 0E 18 STA TIME,X
118C CA DEX
118D 4C 78 11 JMP VBL8
1190 A6 B6 VBL7: LDX JIFF ;Move 60 jiffies (a jiffy is used
1192 E8 INX ;by Pet owners and other people
1193 86 B6 STX JIFF ;to denote a 60th of a second) elapsed?
1195 E0 3C CPX #60
1197 D0 22 BNE VBL9 ;No!
1199 A2 00 LDX #0 ;Yes. Reset jiffy counter
119B 86 B6 STX JIFF
119D A5 B7 LDA STOP ;Has time stopped?
119F D0 2E BNE VBL12 ;Yes.
11A1 A2 05 LDX #5 ;No, so we shall take away a second from
11A3 BD 0E 18 VBL10: LDA TIME,X ;the user's time (har har har)
11A6 38 SEC ;in just the same way as we added one.
11A7 E9 01 SBC #1 ;except for a few changes.
11A9 09 90 ORA #$90
11AB 9D 0E 18 STA TIME,X
11AE C9 9F CMP #$9F ;Like this check for borrow in place
11B0 D0 09 BNE VBL9 ;of a check for carry.
11B2 A9 99 LDA #$99
11B4 9D 0E 18 STA TIME,X
11B7 CA DEX
11B8 4C A3 11 JMP VBL10
11BB A9 00 VBL9: LDA #0 ;Has the user run out of time??
11BD A2 06 LDX #6 ;If so, OR-ing together all of his
11BF 1D 0D 18 VBL11: ORA TIME-1,X ;time-left digets should give a zero
11C2 CA DEX
11C3 D0 FA BNE VBL11
11C5 29 0F AND #$F
11C7 C9 00 CMP #0 ;Does It?
11C9 D0 04 BNE VBL12 ;No
11CB A9 01 LDA #1 ;Yes. Stop time!!!
11CD 85 B7 STA STOP
11CF A9 00 VBL12: LDA #0 ;Store a zero into the ATRACT flag
11D1 85 4D STA ATRACT ;to keep the Atari from futzing with
;our screen colors. . . . Of course
;this means that the user might end
;up with the game field permanently
;embossed on his TV screen. . . .
11D3 AD 78 02 LDA STICK0 ;Take STICK0
11D6 4A LSR A
11D7 4A LSR A ;Divide it by 4
11D8 AA TAX ;Use that number to look up the
11D9 BD 8E 10 LDA JTAB,X ;direction the missile should
11DC 85 B3 STA MDX ;travel in.
11DE CA DEX ; Then subtract one from that
11DF 8A TXA ; (It better not be 0. . . .)
11E0 0A ASL A ;And multiply by eight
11E1 0A ASL A ;to get an index into the
11E2 0A ASL A ;table of the gun pictures
11E3 AA TAX
11E4 A0 00 LDY #0
11E6 BD 92 10 GUNDLP: LDA GUNTAB,X ;Copy the picture of the gun
11E9 99 60 1A STA GUNPOS,Y ;into player zero. Use two
11EC C8 INY ;bytes for each byte in the
11ED 99 60 1A STA GUNPOS,Y ;piture table so the gun is
11F0 E8 INX ;10 dots (32 scan lines) high.
11F1 C8 INY
11F2 C0 10 CPY #16
11F4 D0 F0 BNE GUNDLP
11F6 A5 B2 LDA MX ;Now update missile's X position.
11F8 18 CLC
11F9 65 B3 ADC MDX
11FB 85 B2 STA MX
11FD 8D 04 D0 STA HPOSM0
1200 A5 B4 LDA MY ;Missile Y
1202 F0 26 BEQ VCONT ;No missile
1204 AA TAX
1205 A9 00 LDA #0 ;Erase old missile
1207 9D 80 19 STA MPMBAS+PMDM,X
120A CA DEX ;Hit top of screen?
120B F0 11 BEQ VMDIE ;Yes.
;No.
120D A5 B1 LDA DSCOR ;Hit an airplane with the missile?
120F D0 12 BNE VMHIT ;No.
1211 86 B4 STX MY
1213 A9 FF LDA #$FF ;Draw new missile
1215 9D 80 19 STA MPMBAS+PMDM,X
1218 8E 00 D2 STX AUDF1 ;fweep sound effect
121B 4C 2A 12 JMP VCONT
121E 86 B4 VMDIE: STX MY ;Zero the missile's Y coordinate
1220 4C 2A 12 JMP VCONT ;to kill the missile.
1223 A2 00 VMHIT: LDX #0 ;Since we hit something we should
1225 8E 00 D2 STX AUDF1 ;silence the sound register
1228 86 B4 STX MY ;and zero the missile.
122A A5 B7 VCONT: LDA STOP ;Stoped?
122C D0 16 BNE VCONT2 ;Yes.
122E AD 84 02 LDA STRIG0 ;Check if hunan wants to fire
1231 D0 11 BNE VCONT2 ;No.
1233 A5 B4 LDA MY ;Check if he CAN fire.
1235 D0 0D BNE VCONT2 ;Can't
1237 A9 62 LDA #GUNOFF+2 ;Set the Y coordinate to Just
1239 85 B4 STA MY ;above the muzzle or the gun.
123B A5 B3 LDA MDX ;To get the X coordinate.
123D 0A ASL A ;multiply MDX (the direction the
123E 0A ASL A ;gun is pointing) by 4
123F 18 CLC ;and add to 132 (which is the
1240 69 84 ADC #132 ;CENTER of the Gun)
1242 85 B2 STA MX
1244 A9 FF VCONT2: LDA #$FF ;Reset DLI counter
1246 85 B0 STA DLIC
1248 8D 1E D0 STA HITCLR ;Zero hits.
124B 4C 5F E4 JMP SYSVBV ;Jump to the OS's exit vblank routine.
;
; Main program starts here!!!
;
124E A9 A8 BEGIN: LDA #$A8 ;Missile sound is pure at volume 8
1250 8D 01 D2 STA AUDC1
1253 A9 80 LDA #$80 ;Score sound is a silent fuzz.
1255 8D 03 D2 STA AUDC2
1258 A9 00 LDA #0 ;missile frequency is ultrasonic
125A 8D 00 D2 STA AUDF1
125D A9 30 LDA #$30 ;score frequency is a high fuzz.
125F 8D 02 D2 STA AUDF2
;
; Erase player missile memory space.
;
1262 A2 80 LDX #128
1264 A9 00 LDA #0
1266 9D FF 19 CLOOP: STA MPMBAS+PMDP0-1,X ;We only use Player zero
1269 9D 7F 19 STA MPMBAS+PMDM-1,X ;and the missiles.
126C CA DEX
126D D0 F7 BNE CLOOP
126F A9 00 LDA #0 ;Move all the players and missiles
1271 A2 08 LDX #8 ;off the screen.
1273 9D FF CF PLOOP: STA HPOSP0-1,X
1276 CA DEX
1277 D0 FA BNE PLOOP
1279 A9 2E LDA #$2E ;Enable PM DMA and a normal playfield.
127B 8D 2F 02 STA SDMCTL
127E A9 18 LDA #MPMBAS^ ;Set up the pointer to the Player
1280 8D 07 D4 STA PMBASE ;missile defuns.
1283 A9 03 LDA #3 ;Tell the CTIA to expect PM DMA
1285 8D 1D D0 STA GRACTL
1288 A9 10 LDA #$10 ;Enable fifth player so the
128A 0D 6F 02 ORA GPRIOR ;missiles will be COLOR3
128D 8D 6F 02 STA GPRIOR
1290 8D 1B D0 STA PRIOR
1293 A9 00 LDA #0 ;Zero the missile
1295 85 B4 STA MY
1297 A9 01 LDA #1 ;Stop the player from fireing.
1299 85 B7 STA STOP
129B A9 40 LDA #$40 ;Disable DLI's
129D 8D 0E D4 STA NMIEN
12A0 A9 10 LDA #MDLIST^ ;Set up the vector to our
12A2 8D 31 02 STA SDLSTH ;display list.
12A5 A9 19 LDA #MDLIST&$FF
12A7 8D 30 02 STA SDLSTL
12AA A9 10 LDA #DLIH^ ;Setup the vector to our
12AC 8D 01 02 STA VDBLST+1 ;DLI handler
12AF A9 EA LDA #DLIH&$FF
12B1 8D 00 02 STA VDBLST
12B4 A2 11 LDX #VBLH^ ;Load the address of our
12B6 A0 35 LDY #VBLH&$FF ;verticle blank interrupt
12B8 A9 06 LDA #SETIMM ;handler into X & Y and call
12BA 20 5C E4 JSR SETVBV ;SETVBV to set up the VBLI vector.
12BD A9 C0 LDA #$C0 ;Enable DLI'S
12BF 8D 0E D4 STA NMIEN
12C2 A9 C6 LDA #CLGREN+6 ;Color 0 (score) is green
12C4 8D C4 02 STA COLOR0
12C7 A9 36 LDA #CLRED+6 ;Color 1 (high score) is red.
12C9 8D C5 02 STA COLOR1
12CC A9 18 LDA #CLGOLD+8 ;Color 2 (time) is gold.
12CE 8D C6 02 STA COLOR2
12D1 A9 0A LDA #CLGREY+10 ;Color 3 (missiles) is white.
12D3 8D C7 02 STA COLOR3
;
; Write out the copyright message.
;
12D6 A2 14 LDX #20 ;For the twenty charaters in the message,
12D8 BD 37 10 COPYR1: LDA TMSG-1,X ;load a character,
12DB 20 0E 14 JSR ASTOIN ;Call ASTOIN to get it to internal
12DE 09 C0 ORA #$C0 ;form, change it to color 3, and
12E0 9D FF 17 STA SCORLN-1,X ;Store it on the play field.
12E3 CA DEX
12E4 D0 F2 BNE COPYR1
12E6 A5 13 LDA RTCLOC+1 ;get the real time (4 second ticks)
12E8 18 CLC
12E9 69 03 ADC #3 ;8 to 12 seconds of glory
12EB C5 13 COPYW: CMP RTCLOC+1 ;Wait a while 'till user's read it.
12ED D0 FC BNE COPYW
;
; Erase & initialize score line
;
12EF A2 14 LDX #20 ;Fill score line with spaces.
12F1 A9 00 LDA #0
12F3 9D FF 17 ERASES: STA SCORLN-1,X
12F6 CA DEX
12F7 D0 FA BNE ERASES
12F9 A9 10 LDA #$10 ;Make score ' 0'
12FB 8D 05 18 STA SCORE+5
12FE A9 50 LDA #$50 ;Make high score ' 0'
1300 8D 0C 18 STA HISCOR+5
1303 A9 90 LDA #$90 ;Make time ' 0'
1305 8D 13 18 STA TIME+5
1308 A9 01 REPEAT: LDA #1 ;Stop the player (Just to make
130A 85 B7 STA STOP ;sure!)
130C A9 08 LDA #$08 ;Set up to read the consol
130E 8D 1F D0 STA CONSOL ;switches
1311 AD 1F D0 WAIT: LDA CONSOL
1314 C9 01 CMP #SWSTRT ;The other two switches -- Select
1316 D0 06 BNE WAIT1 ;and option, are not pressed down.
1318 20 2A 14 JSR MAKETP ;If they are pressed down, make a
;copy or this whole program
131B 4C 4E 12 JMP BEGIN ;And reset since the sound registers
;will be messed up. . . .
131E C9 06 WAIT1: CMP #6 ;Is the start switch pressed?
1320 D0 EF BNE WAIT ;Nope. . . .
1322 A9 00 LDA #0 ;Yes. Start game (1)
1324 A2 06 LDX #6 ;Erase time and score but not
1326 9D 0D 18 RESTR2: STA TIME-1,X ;high score.
1329 9D FF 17 STA SCORE-1,X
132C CA DEX
132D D0 F7 BNE RESTR2
132F A9 91 LDA #$91 ;Set the time left to ' 120'
1331 8D 11 18 STA TIME+3
1334 A9 92 LDA #$92
1336 8D 12 18 STA TIME+4
1339 A9 90 LDA #$90
133B 8D 13 18 STA TIME+5
133E A9 10 LDA #$10 ;Set the score to ' 0'
1340 8D 05 18 STA SCORE+5
1343 A9 00 LDA #0 ;let the player shoot.
1345 85 B7 STA STOP
1347 85 B1 STA DSCOR ;Clear out the vblank
1349 85 B6 STA JIFF ;counters.
134B 85 B5 STA DSEC
;
; Set up the PM graphics.
;
134D A2 18 REDRAW: LDX #$18 ;Start at lino 18,
134F A0 00 LDY #0
1351 20 C5 13 CLOOP1: JSR DPLANE ;Draw 8 planes.
1354 C8 INY
1355 C0 08 CPY #8
1357 D0 F8 BNE CLOOP1
;
; Set up 30 second count down timer (used to time rounds)
;
1359 A2 07 LDX #7 ;30 secs = 1800 jiffies.
135B A0 D0 LDY #208
135D A9 03 LDA #3 ;CDT # 3.
135F 8D 2A 02 STA CDTMF3
1362 20 5C E4 JSR SETVBV
1365 A9 C0 LDA #$C0 ;Re-enable DLI's
1367 8D 0E D4 STA NMIEN
136A AD 2A 02 MAIN: LDA CDTMF3 ;Main loop -- if 30 seconds are
136D D0 03 BNE MAIN2 ;up, draw another wave of planes.
136F 4C 4D 13 JMP REDRAW
1372 A0 08 MAIN2: LDY #8 ;Check if all the planes have
1374 A9 00 LDA #0 ;been shot down (i.e. their
1376 19 6C 10 MAIN3: ORA TDX-1,Y ;velocities are all zero)
1379 88 DEY
137A D0 FA BNE MAIN3
137C C9 00 CMP #0
137E D0 0A BNE MAIN4
1380 A9 32 LDA #50 ;If so, player gets 60 points
1382 18 CLC
1383 65 B1 ADC DSCOR
1385 85 B1 STA DSCOR
1387 4C 4D 13 JMP REDRAW ;and a new round.
138A A5 B7 MAIN4: LDA STOP ;Check if player is stopped.
138C F0 DC BEQ MAIN ;Nope.
;Yes:
;
; Player died, so update high score
; and restart.
;
138E A5 13 LDA RTCLOC+1 ;Wait 4 to 8 seconds
1390 18 CLC
1391 69 02 ADC #2
1393 C5 13 HIW: CMP RTCLOC+1 ;for points to drain.
1395 D0 FC BNE HIW
1397 A2 00 LDX #0 ;Check his high score against
1399 BD 07 18 HICHK: LDA HISCOR,X ;his current score.
139C 29 1F AND #$1F ;If his high score is anywhere
139E DD 00 18 CMP SCORE,X ;less than his current score
13A1 F0 05 BEQ HICHK1 ;Equal
13A3 B0 08 BCS NOHI ;HI > score. Stop.
13A5 4C B0 13 JMP NEWHI ;HI < score.
13A8 E8 HICHK1: INX ;NOTE: We check from left to right,
13A9 E0 06 CPX #6 ;unlike the routines in VBIH.
13AB D0 EC BNE HICHK
13AD 4C 08 13 NOHI: JMP REPEAT ;So go and restart the game.
;
; Copy new high score
13B0 A2 06 NEWHI: LDX #6 ;Copy all six digets of the
13B2 BD FF 17 NEWHI1: LDA SCORE-1,X ;score into the high score,
13B5 29 1F AND #$1F ;changing the color at the
13B7 09 40 ORA #$40 ;same time.
13B9 9D 06 18 STA HISCOR-1,X
13BC CA DEX
13BD D0 F3 BNE NEWHI1
13BF 4C 08 13 JMP REPEAT ;Then restart the game.
;
; DPLANE -- pick and draw a plane
;
13C2 00 XTEMP: .BYTE 0 ;Temporary variables
13C3 00 YTEMP: .BYTE 0 ;Used to save state of
13C4 00 TEMPA: .BYTE 0 ;the processer.
13C5 8E C2 13 DPLANE: STX XTEMP ;Save X
13C8 8C C3 13 STY YTEMP ;Save Y
13CB AD 0A D2 DPLAN1: LDA RANDOM ;Get a random number
13CE 29 07 AND #7 ;reduce it to 0-7
13D0 C9 06 CMP #6 ;Is it > 6 ?
13D2 B0 F7 BCS DPLAN1 ;Yes. Pick another one.
13D4 0A ASL A ;No. Multiply by 4
13D5 0A ASL A
13D6 AA TAX
13D7 BD D2 10 LDA TPLANE,X ;And use it to index into
13DA 99 6D 10 STA TDX,Y ;The tplane table for
13DD BD D3 10 LDA TPLANE+1,X ;the velocity, the value.
13E0 99 78 10 STA TVAL,Y ;the width, and the
13E3 BD D4 10 LDA TPLANE+2,X ;index into the plane
13E6 99 83 10 STA TWID,Y ;picture table.
13E9 A9 00 LDA #0
13EB 99 62 10 STA TPX,Y ;Set the X position to 0.
13EE BD D5 10 LDA TPLANE+3,X ;Get the index into the
13F1 AA TAX ;picture table.
13F2 AC C2 13 LDY XTEMP
13F5 A9 08 LDA #8
13F7 8D C4 13 STA TEMPA
13FA BD AA 10 DPLAN3: LDA PTOL,X ;Copy eight bytes from
13FD 99 00 1A STA MPMBAS+PMDP0,Y ;the picture table to
1400 E8 INX ;the player's defun space.
1401 C8 INY
1402 CE C4 13 DEC TEMPA
1405 D0 F3 BNE DPLAN3
1407 98 TYA ;Restore the processor
1408 AA TAX ;state, and return
1409 AC C3 13 LDY YTEMP ;(X has had 0 added to it
140C 60 RTS ;so that the next plane
;drawn will be one position
;lower in the player's defun).
;
; Ascii character in A --> Screen internal character in A
; state saved and restored.
;
; (slightly modified from the internal
; Atari OS routine & uses ROM tables)
140D 00 ASTEMP: .BYTE 0 ;Used to save the state of Y
140E 8C 0D 14 ASTOIN: STY ASTEMP ;Save Y.
1411 A8 TAY ;Copy A into Y
1412 8A TXA
1413 48 PHA ;Save X.
1414 98 TYA
1415 2A ROL A ;Get bits 6 & 5 or character
1416 2A ROL A
1417 2A ROL A
1418 2A ROL A
1419 29 03 AND #3
141B AA TAX
141C 98 TYA
141D 29 9F AND #$9F ;Zero bits 6 & 5 of character
141F 1D F6 FE ORA $FEF6,X ;and fill then with the bits
;from the ROM table, giving
;the internal (screen) code.
1422 A8 TAY ;Restore X & Y registers.
1423 68 PLA
1424 AA TAX
1425 98 TYA
1426 AC 0D 14 LDY ASTEMP
1429 60 RTS
;
; Boot tape writer. Writes out a Boot tape and returns.
;
142A A2 20 MAKETP: LDX #ICTWO ;Choose IOCB two
142C A9 0C LDA #CLOSE ;Close it.
142E 9D 42 03 STA ICCOM,X
1431 20 56 E4 JSR CIOV
1434 A9 14 LDA #CAS^ ;Open the C: device.
1436 9D 45 03 STA ICBAH,X
1439 A9 75 LDA #CAS&$FF
143B 9D 44 03 STA ICBAL,X
143E A9 03 LDA #OPEN
1440 9D 42 03 STA ICCOM,X
1443 A9 08 LDA #OPNOT ;for output
1445 9D 4A 03 STA ICAX1,X
1448 A9 80 LDA #$80 ;short IRQ
144A 9D 4B 03 STA ICAX2,X
144D 20 56 E4 JSR CIOV
1450 A9 00 LDA #PST&$FF ;Write out the program in
1452 9D 44 03 STA ICBAL,X ;one fell swoop (using a
1455 A9 10 LDA #PST^ ;block putchar)
1457 9D 45 03 STA ICBAH,X
145A A9 78 LDA #<PND-PST>&$FF
145C 9D 48 03 STA ICBLL,X
145F A9 04 LDA #<PND-PST>^
1461 9D 49 03 STA ICBLH,X
1464 A9 0B LDA #PUTCHR
1466 9D 42 03 STA ICCOM,X
1469 20 56 E4 JSR CIOV
146C A9 0C LDA #CLOSE ;Close cassette buffer
146E 9D 42 03 STA ICCOM,X
1471 20 56 E4 JSR CIOV
1474 60 RTS
1475 43 3A CAS: .ASCII "C:" ;Name of cassette device.
1477 9B .BYTE EOL
1478 PND = . ;Used by MAKETP to figure
;out what to save. Must
;point to just after last
;byte of program.
0000 .END
COMPUTE! ISSUE 17 / OCTOBER 1981 / PAGE 169
COMPUTE! #16, pg. 86 — To permit “SHOOT” to run on the new (Revision B) ROMs, change line 201 to: BUF$(589,589)=CHR$(95):BUF$(590,590)=CHR$(228). To permit it to run on black and white TVs, change line 202 to: BUF$(97,97)=CHR$(0):BUF$(98,98)=CHR$(0). The source code correction is: 124B 4C 5F E4 JMP SYSVBV.
COMPUTE! ISSUE 18 / NOVEMBER 1981 / PAGE 110
Since SHOOT was published in COMPUTE! #16, we’ve received numerous letters from readers who were having problems with it. Rest assured, if you type in the Boot Tape Maker correctly, it will make a perfect bootable copy of SHOOT.
It is not easy to type in a long computer program listing, especially one like SHOOT, with its huge table of DATA slatements. Here are some tips on how to make it easier, and what to watch out for:
Program listing omitted. It’s identical to the program 1, including the REV. B VBLANK bug.