; ZX80 assembler --- zpace invaders ; ; relocatable code 2 byte numbers and addresses combined ; passes z80-asm tests ; display vertical 12 x horizontal 15 set up by BASIC print of spaces ; (see zpace.inf for BASIC) ; each branch takes circa 1400 cycles which fits in fly-back period ; so no flicker in TV display. ; info stored in video memory starting at (64,12) ; ; Addresses: 0 ........14 NL ; 16........30 NL ; ; 176......190 NL ; ; address (1 byte) stored for you, bomb, laser and some info about SI's ; ; SI initially 5x10 at top, number in (64,30), top left position in e' ; move 1 SI line at a time: line count in h' (-5 initially, bottom) ; no of goes in d' (=0 initially) ; bottom line (176,..,190) is you (in c', initially 183) ; laser fired from you on bottom line (max 1) in l' ; bomb dropped from SI (always 1) in b' ; on screen: SI are "S", bomb is "*", laser is "." ; LD BC, 75 ; offset to INIT (LSB=75 MSB=0) ADD HL,BC PUSH HL ; needed since JR only ranges +/-128 POP IX ; HL contained start address, IX is +75: INIT: EXX ; store on alt registers LD H, 251 ; sline=-5 line of SI to move first (bottom) LD A, (16415) ; number of frames mod 7-> quasi random bomb position 64,31 AND 7 LD B,A ; bomb position LD C, 183 ; your position on bottom line (176...190) LD DE, 0 ; no of goes, lowest position of a SI LD L,H ; laser position EXX LD HL, (16396) ; start of display buffer ( 15 wide 12 high ) LD A, 5 ; put symbol "56"=S into 5*10 space invader block L2: LD B, 10 L1: INC HL LD (HL), 56 DJNZ L1 ; decrements B until 0 LD BC, 6 ; start of next line ADD HL,BC DEC A JR NZ L2 NOP LD (IY+30), 50 ; number of SI LD HL, (16400) ; display end 64,16 LD BC, (16420) ; next position in line 64,36 (B=row, C=across) INC B XOR A CP C LD A, 118 ; newline C=0 then newline already signalled JR Z G1 ; check label G1 (was 2 in code tested, ie GG1!) NLL: LD (HL),A G1: INC HL GG1: DJNZ NLL ; fill rest of display with newlines JR INIT RET1: POP HL POP HL RET2: LD H, 0 LD L, (IY+30) RET ; end of game INIT: LD HL, (16396) ; reload l,b,y --------------- INC HL EX DE,HL LD H, 0 EXX LD A,L EXX LD L,A ; laser l status ADD HL,DE CP 191 JR NC NOL ; check > 191 ie no laser LD A, 56 CP (HL) ; check if SI (symbol 56) on l site JR Z HIT LD (HL), 27 ; place l symbol (.) DEL2: PUSH HL ; delay POP HL JR ENDL NOL: JR DEL1 DEL1: NOP ; delay JR DEL2 HIT: LD (HL), 184 ; splat: symbol inverse S DEC (IY+30) ; one less SI JR Z RET2 ; if no SI left -> RET2 END: killed all SI ENDL: PUSH HL LD H, 0 EXX LD A,C ; y -> L EXX LD L,A ADD HL,DE PUSH HL LD A, 56 CP (HL) ; check if SI on y -> RET1 JR Z RET1 LD (HL), 128 ; else char 128 (inverse space) LD H, 0 EXX LD A,B EXX LD L,A ; b -> L ADD HL,DE LD A,(HL) CP 38 ; see what bomb does l(27) sp(0) | SI(56,184) y(128) JR NC, NOB LD (HL), 20 ; load * NOB: JR NC, DB ; no bomb DB: CP 128 JR Z RET1 ; bomb on y -> RET1 END of game PUSH HL FRM: LD (IY+35), 56 ; output to Display--------------------- LD A, 15 ; code copied from ROM: IY=64,00 OUT (255) A LD A, 236 LD B, 25 LD HL, (16396) ; 64,12 SET 7, H CALL 429 ; 1,173 LD A, 243 INC B DEC HL DEC (IY+35) JR FRD FRD: CALL 429 IN A, (254) ; end copied code---------------- EXX INC D ; number of goes LD A,D AND 3 ; bomb and laser speed (7 is slower) JR Z DLBY ; ->->-> delete l b y (only exit from frm loop) LD A,E EXX LD C,A LD HL, (16396) INC HL LD B, 0 ADD HL,BC PUSH HL ; save address of Smin +1 LD D,C ; Smin EXX ; calculate b' new (random) bomb origin LD A,D ; quasi-random - based on other info RRA RRA ADD A,B ADD A,L ; N_goes/4+b+l AND 23 ; 00010111 : pseudo rand 0..7 16..23 ADD A, 1 ; +1 EXX ; top 2 rows 0..9xxxxx16...25 from Smin LD C,A ; C stores rnd ADD HL,BC ; HL points at rnd + Smin LD A, 26 SUB C LD B,A ; 26 - rnd: count for search from rnd to end LD A, 56 ; LD E,B ; if no SI on top 2 rows: use rnd (was 22 -BUG) NOP BC1: CP (HL) ; SI at address? JR NZ SK1 LD E,B ; b1_loop keep first SI position found (rel 26-rnd) INC A ; so ignore later sites SK1: INC HL DJNZ BC1 ; step through top 2 rows of SI from rnd EX AF,AF' LD A,E ; first SI position: (26-rnd-x if at rnd+x) SUB 26 ADD A,C LD E,A ; store b1_loop -(26-rnd) ie -x (rel rnd) POP HL ; Smin LD B,C ; rnd EX AF,AF' BC2: CP (HL) ; search for SI if not found above from 0 to rnd JR NZ SK2 LD E,B ; b2_loop (rnd-x) if at x (rel 1) INC A ; ignore SI if found SK2: INC HL DJNZ BC2 LD A,C SUB E ; rnd + x ie position rel 1 ADD A,D ; LD (16415), A ; 64,31 Smin+b' LD B, 12 DLB: DJNZ DLB ; delay JR FRM DLBY: EXX ; delete l b y ---------------------- LD B, 0 POP HL LD A, 20 CP (HL) JR NZ NOBD ; check if * (bomb) on screen LD (HL) B ; replace * by 0 NOBD: POP HL LD (HL) B POP HL EXX LD A,L CP 191 ; check if laser in use (< 191) EXX LD A,(HL) JR NC NOLD LD (HL) B ; replace by 0 NOLD: CP 184 ; check if inverse S on screen (ie SI hit) EXX JR NZ NOHIT LD L, 254 ; flag l as not in use NOHIT: LD A,D EXX AND 31 ; SI moving speed (63 slower) JR Z SIM ; to SI move LD B, 0 ; MOVE l b y ------------------------------ LD C, 254 IN A (C) ; read keyboard ; 1:left, 2:right, 7:fire CPL LD E,A ; key in E EXX LD A,C EXX LD D,A ;y EXX LD A,L ;l EXX LD C, 191 ; only fire if l is (off) ie > 191 SCF BIT 3, E JR Z NOF CP C NOF: JR C LSM LD A,D ; set l from y if was > 191 and key ON LSM: CP C JR NC LOFF SUB 16 ; move up 1 line LOFF: EXX LD L,A EXX LD A,D BIT 0, E ; move L ? JR Z NOMV CP 176 ; check allowed move 176---190 NOMV: JR Z NOTL DEC A NOTL: BIT 1, E ; move R ? JR Z NOMV1 CP 190 NOMV1: JR Z NOTR INC A NOTR: EXX LD C,A ; store y LD A,B ADD A,16 ; move b down 1 line LD B, (IY+31) ; get b' CP 191 JR NC NEWB LD B,A ; keep old b if still on screen NEWB: EXX LD B, 47 ; delay DLL: DJNZ DLL JP (IX) NOP SIM: EXX ; SI MOVE ---------------- zig-zag------------------- LD A,E ; moves 1 block of 10 at a time EXX LD C,A ; Smin (address top left of SI block) AND 7 ; 00000111 mask BIT 4, C ; 16's bit: so if odd or even row JR Z EV ; calc shift of SI CP 0 ; Smin moves 0 1 2 3 4 5 21 20 .. 16 32 33 34 ... LD A, 255 ; -1 JR NZ XEND ; ie delS : +1, -1 or +16 (down row) ADD A, 17 XEND: NOP JR NXT EV: CP 5 ; ie last place to right to will move down LD A, 1 ; +1 JR NZ XEND1 ADD A,15 ; +16 XEND1: JR NXT NXT: LD D,A ; delS in D ADD A,C ; LD C,A ; Smin+delS in C SUB 127 ; C -(191-64) LHS of new bottom line of SI rel 191 JR C NBOT ; not beyond bottom line AND 240 ; bottom line of SI rel 191 (line*16) ( 11110000 ) CP 48 ; test: top of SI will be on bottom line JR Z RETT ; SI are on bottom row -------> END (was NZ in test code) ADD A,16 NEG ; -16 or -32 or -48 ADD A,C ; shift Smin+delS up to ignore empty lower rows LD C,A ; (so transfer an extra empty lines) NOP ; needed if all bottom rows of SI are killed JR FN NBOT: LD B, 4 ; delay SLF: DJNZ SLF FN: LD A,D ; Smin EXX ; eval source, dest for block tranfers of 10 INC H ; filling with zeroes keep other symbols JR NZ NTOP ; H contains block number -1 -2 -3 -4 -5 (increment) LD H, 251 ; bottom line ADD A,E ; Smin+delS LD E,A ; update Smin if top line moving LD A, 9 ; 9 to move topline JR SKP NTOP: LD A,H ; not top line CPL RLCA RLCA RLCA RLCA ; -H * 16 ADD A,25 ; +9+16 : dest 25, .., 105 (top line 9) SKP: EXX ADD A,C ; Smax (dest) SUB D ; Smax (source) CP (HL) LD B, 6 ; delay DDD: DJNZ DDD LD E,A LD A,D LD BC, 2560 ; 10,0 in BC LD D,C LD HL, (16396) ; 64,12 BIT 7, A JR NZ INX NOP ; DelS=1,16 ADD HL,DE INC HL LD E,A EX DE,HL ADD HL,DE EX DE,HL DCL: LD A, (HL) ; loop LD (DE), A ; move SI info to DE LD (HL), C ; fill old site with zero DEC HL DEC DE DJNZ DCL ; loop 10(from B) JP (IX) ; to INIT -----------------------> INX: LD A,E SUB 8 ; delS = -1 LD E,A ADD HL,DE LD E,L LD D,H DEC DE INCL: LD A,(HL) ; loop LD (DE),A ; move SI info LD (HL),C ; fill zero INC HL INC DE DJNZ INCL ; loop 10(from B) JP (IX) ; to INIT -------------------------> RETT: LD H, 0 LD L, (IY+30) RET