Bang Goes Your Code

!0.......^.........^.........^..


!B


\H11\H07\H10\H02 B A N G


\H11\H07\H10\H00 GOES YOUR CODE





!2.......^.........^.........^.........^.........^.........^....


Has the razzle-dazzle gone out of your programs? Simon Lane's


got some explosive ideas to stun you ...


!1.......^.........^.........^.........^........





Have you ever had that feeling of anti-climax


when, having successfully obliterated an alien


(or whatever) in some otherwise superbly written


Basic program, it simply disappears into thin


air without any kind of graphic reward? Well,


now you'll be able to remedy this omission by


simply calling one of these interrupt-driven


machine code explosion routines at the approp-


riate point in your program. Just read the


instructions, type in the object code, and off


you go.


The assembly language listings have been


produced using the Hisoft GENS assembler, which


uses a '#' symbol to denote Hex numbers. If you


have an assembler you can type in the source


code and assemble it yourself. This will allow


you the added joy of making your own alterations


to the programs - certainly, it's a lot less


boring than entering the object code straight.


However, without an assembler this is exactly


what you will have to do - using either a suit-


able monitor program, or the short Hex loader


provided as a last resort.


To use the Hex loader, first you'll have to


enter the start address (in decimal) as given in


the instructions for each routine; that has to


be followed by all the Hex object code given in


column two of the assembler listing. For


example, to enter





!0.......^.........^.........^..


!B


10 REM ***********************


20 REM HEX LOADER


30 REM ***********************


40 DEF FN d(h$)=CODE h$-48-(32


AND h$>="a")-(7 AND h$>="A")


50 INPUT "Start address:";l


60 INPUT (l);">";h$


70 POKE l,FN d(h$(1))*16+FN d(


h$(2))


80 LET l=l+1: LET h$=h$(3 TO )


90 IF h$>"" THEN GO TO 70


100 GO TO 60





!2.......^.........^.........^.........^.........^.........^....


Those without an assembler can use the above program to type in


the Hex code.


!1.......^.........^.........^.........^........





the Missile Command routine, you would type


65023 (Enter), 16FE (Enter), AF (Enter), 32D2FE


... 00FF (Enter). Once that's out of the way,


you can break out of the program by deleting one


of the quotes and typing STOP.





!0.......^.........^.........^..


!B


MISSILE COMMAND


EXPLOSION (MCEXP)


!1.......^.........^.........^.........^........


Anyone who's ever been in an amusement arcade


must surely have come across the Missile Command


game at some time or other. There the explosions


are displayed as circles which get larger and


larger and then shrink away to nothing; my first


routine is an attempt to simulate this effect.


The object code should be entered into memory


starting at 65023 (FDFF Hex) and, just as a


check, the first address at which no object code


should be entered (that is, the address at which


you STOP the Hex loader) should be 65256 (FEEB


Hex).


The routine works by drawing a series of octa-


gons on the screen, starting at the coordinates


stored in XPOS and YPOS (see below). When a


'radius' equal to the contents of LIMIT is


reached, the octagons are 'undrawn', but this


time in reverse order. This gives an effect very


similar to a circle growing and then





!0.......^.........^.........^..


10 REM ***********************


20 REM MCEXP DEMO


30 REM ***********************


40 REM


50 REM ASSIGN VARIABLES


60 REM


70 LET xpos=65236


80 LET ypos=65237


90 LET limit=65238


100 LET speed=65239


110 LET done=65240


120 REM


130 REM INITIALISE MCEXP


140 REM


150 POKE xpos,128


160 POKE ypos,88


170 POKE limit,87


180 POKE speed,1


190 REM


200 REM CALL MCEXP


210 REM


220 RANDOMIZE USR 65025


230 REM


240 REM FLASH BORDER UNTIL END


250 REM


260 BORDER RND*7


270 IF PEEK done THEN STOP


280 GO TO 260





!2.......^.........^.........^.........^.........^.........^....


The Missile Command demo: produces an explosion at the centre of


the screen.


!1.......^.........^.........^.........^........





!B


shrinking away - without the problems associated


with drawing circles (slowness and/or large


look-up tables). Note that when the octagons are


drawn on the screen, XOR plotting is used. This


gives the same effect as using PLOT OVER 1 from


Basic.


Once you've typed in the object code it's


advisable to save it immediately, just in case


you inadvertently manage to crash the program.


Enter SAVE "mcexp" CODE 65023,233 to save to


tape, and SAVE *"m";1;"mcexp" CODE 65023,233 to


save to Microdrive cartridge. Then, type in and


run the MCEXP DEMO program; if everything is as


it should be, and explosion should be produced


that starts at the centre of the screen and then


fills it.


To use the routine in your own programs, you


just have to POKE the locations below with the


appropriate values and then use the command


RANDOMIZE USR 65025. The variables used in the


program are as follows:


!0.......^.........^.........^..


XPOS: 65236 (FED4 Hex)


YPOS: 65237 (FED5 Hex)


!1.......^.........^.........^.........^........


These should be POKEd with the x and y coord-


inates of the point where the centre of the


explosion is required.


!0.......^.........^.........^..


LIMIT: 65238 (FED6 Hex)


!1.......^.........^.........^.........^........


The radius of the required explosion. Note XPOS


- LIMIT 0, XPOS + LIMIT 255, YPOS - LIMIT 0,


YPOS + LIMIT 175,


!0.......^.........^.........^..


SPEED: 65239 (FED7 Hex)


!1.......^.........^.........^.........^........


The speed of the explosion. Note that one is


fast, 255 is slow. Total time of explosion =


(LIMIT * SPEED + 1)/25 seconds (approx). Large


explosions take considerably longer.


!0.......^.........^.........^..


DONE: 65240 (FED8 Hex)


!1.......^.........^.........^.........^........


This location can be PEEKed to determine whether


or not the explosion has been completed (since


the routine is interrupt-driven, the Basic


program continues to run while the machine code


is executed). A zero indicates that the explos-


ion is still taking place and a one indicates


that it has finished. Note that commands of the


form "IF PEEK done ..." can therefore be used in


your programs.


It's advisable to assign the values above to


Basic variables at the start of your program.


This approach is used in each of the demon-


stration programs.





!2.......^.........^.........^.........^.........^.........^....


!B


FDFF ORG #FDFF


FDFF 16FE DEFW MCEXP


;Initialise variables and interrupts


FE01 AF GO XOR A


FE02 32D8FE LD (DONE),A


FE05 32DAFE LD (SIZE),A


FE08 32DFFE LD (INOUT),A


FE0B 3C INC A


FE0C 32D9FE LD (COUNT),A


FE0F 3EFD LD A,#FD ;This makes Z80 jump to the sub-


FE11 ED47 LD I,A ;routine whose address is stored


FE13 ED5E IM 2 ;at FDFF on each interrupt


FE15 C9 RET


;This code is executed every 0.02 secs


FE16 C5 MCEXP PUSH BC


FE17 D5 PUSH DE


FE18 E5 PUSH HL


FE19 F5 PUSH AF


FE1A DDE5 PUSH IX


;Draw an octagon every (SPEED)/50 secs


FE1C 21D9FE LD HL,COUNT


FE1F 35 DEC (HL)


FE20 C2A4FE JP NZ,RET


FE23 3AD7FE LD A,(SPEED)


FE26 77 LD (HL),A


FE27 2AD4FE LD HL,(XPOS)


FE2A 3ADAFE LD A,(SIZE)


FE2D A7 AND A


FE2E 2005 JR NZ,NOT0


;If (SIZE)=0 then plot a single point ...


FE30 CDADFE CALL PLOT


FE33 1848 JR ENDPLT


;otherwise draw an octagon of the appropriate size


FE35 5F NOT0 LD E,A


FE36 57 LD D,A


FE37 CB3A SRL D


FE39 19 ADD HL,DE


FE3A 1100FF LD DE,#FF00 ;Down


FE3D DD21E0FE LD IX,DIRTAB


FE41 0E04 LD C,#04


FE43 FE01 MLOOP CP #01


FE45 2809 JR Z,NOGO


FE47 47 LD B,A


FE48 CB80 RES 0,B


;Draw straight line


FE4A 19 STRT ADD HL,DE


FE4B CDADFE CALL PLOT


FE4E 10FA DJNZ STRT


FE50 47 NOGO LD B,A


FE51 04 INC B


FE52 CB38 SRL B


FE54 ED53DBFE LD (DE1),DE


FE58 DD5E00 LD E,(IX+#00)


FE5B DD5601 LD D,(IX+#01)


FE5E ED53DDFE LD (DE2),DE


;Draw diagonal line


FE62 19 DIAG ADD HL,DE


FE63 CB47 BIT 0,A


FE65 CCADFE CALL Z,PLOT


FE68 ED5BDBFE LD DE,(DE1)


FE6C 19 ADD HL,DE


FE6D CDADFE CALL PLOT


FE70 ED5BDDFE LD DE,(DE2)


FE74 10EC DJNZ DIAG


FE76 DD23 INC IX ;Point to next


FE78 DD23 INC IX ;entry in DIRTAB


FE7A 0D DEC C


FE7B 20C6 JR NZ,MLOOP


FE7D 3ADFFE MLOOP LD A,(INOUT)


FE80 A7 AND A


FE81 21DAFE LD HL,SIZE


FE84 2010 JR NZ,IN


FE86 3AD6FE LD A,(LIMIT)


FE89 BE CP (HL)


FE8A 2803 JR Z,CHANGE


FE8C 34 INC (HL) ;Grow


FE8D 1815 JR RET


;Change from growing to shrinking


FE8F 3E01 CHANGE LD A,#01


FE91 32DFFE LD (INOUT),A


FE94 180E JR RET


FE96 3D IN DEC A


FE97 BE CP (HL)


FE98 2009 JR NZ,INOK


;Explosion complete


FE9A 3E01 LD A,#01


FE9C 32D8FE LD (DONE),A


FE9F ED56 IM 1


FEA1 1801 JR RET


FEA3 35 INOK DEC (HL) ;Shrink


;Restore registers & jump to ROM interrupt routine


FEA4 DDE1 RET POP IX


FEA6 F1 POP AF


FEA7 E1 POP HL


FEA8 D1 POP DE


FEA9 C1 POP BC


FEAA C33800 JP #0038


;Invert point if growing, unplot if shrinking


FEAD E5 PLOT PUSH HL


FEAE F5 PUSH AF


FEAF 3ADFFE LD A,(INOUT)


FEB2 A7 AND A


FEB3 2008 JR NZ,UNPLOT


;Invert point


FEB5 CDC5FE PLOTX CALL PIXAD


FEB8 2F CPL


FEB9 AE XOR (HL)


FEBA 77 LD (HL),A


FEBB 1805 JR PLTRET


;Unplot point


FEBD CDC5FE UNPLOT CALL PIXAD


FEC0 A6 AND (HL)


FEC1 77 LD (HL),A


FEC2 F1 PLTRET POP AF


FEC3 E1 POP HL


FEC4 C9 RET


;Convert x,y coords into d.file address & bit map


FEC5 C5 PIXAD PUSH BC


FEC6 44 LD B,H


FEC7 4D LD C,L


FEC8 CDAA22 CALL #22AA


FECB 47 LD B,A


FECC 04 INC B


FECD 3EFE LD A,#FE


FECF 0F PIXEL RRCA


FED0 10FD DJNZ PIXEL


FED2 C1 POP BC


FED3 C9 RET


;Variables


FED4 64 XPOS DEFB 100 ;X,Y coordinates of centre


FED5 64 YPOS DEFB 100 ;of explosion on screen


FED6 0A LIMIT DEFB 10 ;Max. radius of explosion


FED7 05 SPEED DEFB 5 ;Speed of explosion


FED8 00 DONE DEFB 0 ;Flag to indicate end of explosion


FED9 00 COUNT DEFB 0 ;Interrupts before next octagon


FEDA 00 SIZE DEFB 0 ;Current radius of explosion


FEDB 0000 DE1 DEFW 0 ;Horizontal and vertical


FEDD 0000 DE2 DEFW 0 ;components of diagonal


FEDF 00 INOUT DEFB 0 ;0=growing; 1=shrinking


;Table of directions


FEE0 FFFF DIRTAB DEFW #FFFF ;Left


FEE2 0001 DEFW #0100 ;Up


FEE4 0100 DEFW #0001 ;Right


FEE6 000F DEFW #FF00 ;Down


!0.......^.........^.........^..





!B


DOT FADE EXPLOSION (FADE)


!1.......^.........^.........^.........^........


Technically this isn't really an explosion at


all. What happens here is that the object to be


"de-materialised" fades away dot-by-dot. The


start address for the object code is 64767 (FCFF


Hex), and the first unused address should be


64922 (FD9A Hex). When you've entered the code,


save using SAVE "fade" CODE 64767,155 or SAVE





!0.......^.........^.........^..


10 REM ***********************


20 REM FADE DEMO


30 REM ***********************


40 REM


50 REM ASSIGN VARIABLES


60 REM


70 LET dpos=64914


80 LET apos=64915


90 LET dlim=64916


100 LET alim=64917


110 LET speed=64918


120 LET done=64919


130 REM


140 REM FILL SCREEN


150 REM


160 FOR i=1 TO 704


170 PRINT CHR$ (RND*95+32);


180 NEXT i


190 REM


200 REM INITIALISE FADE


210 REM


220 POKE dpos,0


230 POKE apos,0


240 POKE dlim,22


250 POKE alim,32


260 POKE speed,10


270 REM


280 REM CALL FADE


290 REM


300 RANDOMIZE USR 64769


310 REM


320 REM WAIT UNTIL END


330 REM


340 IF PEEK done THEN STOP


350 GO TO 340





!2.......^.........^.........^.........^.........^.........^....


The Dot Fade demo: fills an area of the screen with random


characters and erases them pixel-by-pixel.


!1.......^.........^.........^.........^........





!B


*"m";1;"fade" CODE 64767,155 - for tape or


Microdrive respectively.


If everything has gone OK so far, then try out


the FADE DEMO program. This will (hopefully)


fill the screen with random characters and then


erase them pixel-by-pixel. To use the routine


from your own programs, just POKE the locations


shown below with the appropriate values and then


use the command RANDOMIZE USR 64769. The


variables used are:


!0.......^.........^.........^..


DPOS: 64914 (FD92 Hex)


APOS: 64915 (FD93 Hex)


!1.......^.........^.........^.........^........


These should be POKEd with the down and across


coordinates of the top left character square in


the area to be exploded. Note that this is a


different approach to the one used in MCEXP


which uses x,y coordinates (this is, pixel


coordinates).


!0.......^.........^.........^..


DLIM: 64916 (FD94 Hex)


ALIM: 64917 (FD95 Hex)


!1.......^.........^.........^.........^........


These should be POKEd with the size of the area


in character squares, down and across respec-


tively.


!0.......^.........^.........^..


SPEED: 64918 (FD96 Hex)


!1.......^.........^.........^.........^........


The speed of the explosion. Again, one is fast,


255 is slow. Total time of explosion = SPEED/3


seconds (approx). Large areas may take consider-


ably longer.


!0.......^.........^.........^..


DONE: 64919 (FD97 Hex)


!1.......^.........^.........^.........^........


The same as for MCEXP.





!2.......^.........^.........^.........^.........^.........^....


!B


FCFF ORG #FCFF


FCFF 15FD DEFW FADE


;Initialise variables and interrupts


FD01 AF GO XOR A


FD02 3297FD LD (DONE),A


FD05 3C INC A


FD06 3298FD LD (COUNT),A


FD09 3E08 LD A,#08


FD0B 3299FD LD (ROUND),A


FD0E 3EFC LD A,#FC ;This makes Z80 jump to the sub-


FD10 ED47 LD I,A ;routine whose address is stored


FD12 ED5E IM 2 ;at FCFF on each interrupt


FD14 C9 RET


;This code is executed every 0.02 secs


FD15 C5 FADE PUSH BC


FD16 D5 PUSH DE


FD17 E5 PUSH HL


FD18 F5 PUSH AF


;Erase some dots every (SPEED)/50 secs


FD19 2198FD LD HL,COUNT


FD1C 35 DEC (HL)


FD1D 2047 JR NZ,RET


FD1F 3A96FD LD A,(SPEED)


FD22 77 LD (HL),A


FD23 ED5B92FD LD DE,(DPOS)


FD27 ED4B94FD LD BC,(DLIM)


FD2B CB21 SLA C ;Convert number of


FD2D CB21 SLA C ;rows to number of


FD2F CB21 SLA C ;hires screen lines


FD31 2199FD LD HL,ROUND


FD34 35 DEC (HL)


FD35 2816 JR Z,END


;Erase some dots in the specified area


FD37 CD6DFD CALL CHRADR


FD3A 50 MLOOP1 LD D,B


FD3B 5D LD E,L


FD3C ED5F BYTE1 LD A,R ;Reasonably random number


FD3E A6 AND (HL)


FD3F 77 LD (HL),A


FD40 2C INC L


FD41 10F9 DJNZ BYTE1


FD43 42 LD B,D


FD44 6B LD L,E


FD45 CD7CFD CALL NXTLIN


FD48 0D DEC C


FD49 20EF JR NZ,MLOOP1


FD4B 1819 JR RET


;Clear the specified area


FD4D CD6DFD END CALL CHRADR


FD50 50 MLOOP2 LD D,B


FD51 5D LD E,L


FD52 AF XOR A


FD53 77 BYTE2 LD (HL),A


FD54 2C INC L


FD55 10FC DJNZ BYTE2


FD57 42 LD B,D


FD58 6B LD L,E


FD59 CD7CFD CALL NXTLIN


FD5C 0D DEC C


FD5D 20F1 JR NZ,MLOOP2


FD5F 3E01 LD A,#01


FD61 3297FD LD (DONE),A


FD64 ED56 IM 1


;Restore registers & jump to ROM interrupt routine


FD66 F1 RET POP AF


FD67 E1 POP HL


FD68 D1 POP DE


FD69 C1 POP BC


FD6A C33800 JP #0038


;Convert d,a character position to d.file address


FD6D 7B CHRADR LD A,E


FD6E 0F RRCA


FD6F 0F RRCA


FD70 0F RRCA


FD71 E6E0 AND #E0


FD73 82 ADD A,D


FD74 6F LD L,A


FD75 7B LD A,E


FD76 E618 AND #18


FD78 F640 OR #40


FD7A 67 LD H,A


FD7B C9 RET


;Find address of next line from address of present


FD7C 7C NXTLIN LD A,H


FD7D 0F RRCA


FD7E 0F RRCA


FD7F 0F RRCA


FD80 C620 ADD A,#20


FD82 3009 JR NC,DONE2


FD84 67 LD H,A


FD85 7D LD A,L


FD86 C620 ADD A,#20


FD88 6F LD L,A


FD89 3001 JR NC,DONE1


FD8B 24 INC H


FD8C 7C DONE1 LD A,H


FD8D 07 DONE2 RLCA


FD8E 07 RLCA


FD8F 07 RLCA


FD90 67 LD H,A


FD91 C9 RET


;Variables


FD92 00 DPOS DEFB 0 ;Down and across position


FD93 00 APOS DEFB 0 ;of explosion on screen


FD94 05 DLIM DEFB 5 ;Size of explosion


FD95 20 ALIM DEFB 32 ;in character squares


FD96 32 SPEED DEFB 50 ;Speed of explosion


FD97 00 DONE DEFB 0 ;Flag to indicate end of explosion


FD98 00 COUNT DEFB 0 ;Interrupts to go before next fade


FD99 00 ROUND DEFB 0 ;Number of fades to go


!0.......^.........^.........^..





!B


COLOUR FLASH EXPLOSION (FLASH)


!1.......^.........^.........^.........^........


In this explosion, various different patterns of


random dots flash up onto the screen in many


colours and then disappear. The routine itself


is very similar to the FADE routine, and using


it is exactly the same except that the numbers


are different. Therefore I'll just give you the





!0.......^.........^.........^..


10 REM ***********************


20 REM FLASH DEMO


30 REM ***********************


40 REM


50 REM ASSIGN VARIABLES


60 REM


70 LET dpos=64706


80 LET apos=64707


90 LET dlim=64708


100 LET alim=64709


110 LET speed=64710


120 LET done=64711


130 REM


140 REM FILL SCREEN


150 REM


160 FOR i=1 TO 704


170 PRINT CHR$ (RND*95+32);


180 NEXT i


190 REM


200 REM INITIALISE FLASH


210 REM


220 POKE dpos,0


230 POKE apos,0


240 POKE dlim,22


250 POKE alim,32


260 POKE speed,5


270 REM


280 REM CALL FLASH


290 REM


300 RANDOMIZE USR 64513


310 REM


320 REM WAIT UNTIL END


330 REM


340 IF PEEK done THEN STOP


350 GO TO 340





!2.......^.........^.........^.........^.........^.........^....


The Colour Flash demo: flashes a number of random characters in


different colours and then erases them.


!1.......^.........^.........^.........^........





!B


numbers, as it were, and you can use the text


from FADE as a guide where necessary. But, there


is one other important difference - the demon-


stration program is called FLASH DEMO and it


fills the screen with random characters and then


explodes them appropriately. Here are the


various numbers:





Start address: 64511 (FBFF Hex)


First unused address: 64714 (FCCA Hex)


Saving: SAVE "flash" CODE 64511,203 or SAVE


*"m";1;"flash" CODE 64511,203 (for tape or


Microdrive respectively).


To use from Basic: RANDOMIZE USR 64513


Variables:


!0.......^.........^.........^..


DPOS: 64706 (FCC2 Hex)


APOS: 64707 (FCC3 Hex)


DLIM: 64708 (FCC4 Hex)


ALIM: 64709 (FCC5 Hex)


SPEED: 64710 (FCC6 Hex)


DONE: 64711 (FCC7 Hex)


!1.......^.........^.........^.........^........


Note that each of the routines occupies a diff-


erent area of memory (they don't overlap). It's


therefore possible to have all three routines in


memory at the same time - although you'll only


ever have one explosion occurring on the screen


at any one time. Also, the use of BEEP, LOAD or


SAVE while an interrupt is occurring will tempo-


rarily halt it. Happy zapping!





!2.......^.........^.........^.........^.........^.........^....


!B


FBFF ORG #FBFF


FBFF 15FC DEFW FLASH


;Initialise variables and interrupts


FC01 AF GO XOR A


FC02 32C7FC LD (DONE),A


FC05 3C INC A


FC06 32C8FC LD (COUNT),A


FC09 3E08 LD A,#08


FC0B 32C9FC LD (ROUND),A


FC0E 3EFB LD A,#FB ;This makes Z80 jump to the sub-


FC10 ED47 LD I,A ;routine whose address is stored


FC12 ED5E IM 2 ;at FBFF on each interrupt


FC14 C9 RET


;This code is executed every 0.02 secs


FC15 C5 FLASH PUSH BC


FC16 D5 PUSH DE


FC17 E5 PUSH HL


FC18 F5 PUSH AF


;Flash every (SPEED)/50 secs


FC19 21C8FC LD HL,COUNT


FC1C 35 DEC (HL)


FC1D 2077 JR NZ,RET


FC1F 3AC6FC LD A,(SPEED)


FC22 77 LD (HL),A


FC23 ED5BC2FC LD DE,(DPOS)


FC27 ED4BC4FC LD BC,(DLIM)


FC2B CB21 SLA C ;Convert number of


FC2D CB21 SLA C ;rows to number of


FC2F CB21 SLA C ;hires screen lines


FC31 21C9FC LD HL,ROUND


FC34 35 DEC (HL)


FC35 2846 JR Z,END


;Flash specified area


FC37 CD9DFC CALL CHRADR


FC3A 50 MLOOP1 LD D,B


FC3B 5D LD E,L


FC3C ED5F BYTE1 LD A,R


FC3E 77 LD (HL),A


FC3F ED5F LD A,R ;Reasonably random number


FC41 0F RRCA


FC42 0F RRCA


FC43 AE XOR (HL)


FC44 77 LD (HL),A


FC45 2C INC L


FC46 10F4 DJNZ BYTE1


FC48 42 LD B,D


FC49 6B LD L,E


FC4A CDACFC CALL NXTLIN


FC4D 0D DEC C


FC4E 20EA JR NZ,MLOOP1


FC50 2AC2FC LD HL,(DPOS)


;Convert d,a position to address in attribute file


FC53 7C LD A,H


FC54 2600 LD H,#00


FC56 0605 LD B,#05


FC58 29 DOUBLE ADD HL,HL


FC59 10FD DJNZ DOUBLE


FC5B B5 OR L


FC5C 6F LD L,A


FC5D 7C LD A,H


FC5E F658 OR #58


FC60 67 LD H,A


;Colour in specified area with (ROUND) ink


FC61 ED4BC4FC LD BC,(DLIM)


FC65 3AC9FC LD A,(ROUND)


FC68 57 LD D,A


FC69 5D ALINE LD E,L


FC6A C5 PUSH BC


FC6B 7E ABYTE LD A,(HL)


FC6C E6F8 AND #F8


FC6E B2 OR D


FC6F 77 LD (HL),A


FC70 2C INC L


FC71 10F8 DJNZ ABYTE


FC73 6B LD L,E


FC74 0E20 LD C,#20


FC76 09 ADD HL,BC


FC77 C1 POP BC


FC78 0D DEC C


FC79 20EE JR NZ,ALINE


FC7B 1819 JR RET


;Clear specified area


FC7D CD9DFC END CALL CHRADR


FC80 50 MLOOP2 LD D,B


FC81 5D LD E,L


FC82 AF XOR A


FC83 77 BYTE2 LD (HL),A


FC84 2C INC L


FC85 10FC DJNZ BYTE2


FC87 42 LD B,D


FC88 6B LD L,E


FC89 CDACFC CALL NXTLIN


FC8C 0D DEC C


FC8D 20F1 JR NZ,MLOOP2


FC8F 3E01 LD A,#01


FC91 32C7FC LD (DONE),A


FC94 ED56 IM 1


;Restore registers & jump to ROM interrupt routine


FC96 F1 RET POP AF


FC97 E1 POP HL


FC98 D1 POP DE


FC99 C1 POP BC


FC9A C33800 JP #0038


;Convert d,a character position to d.file address


FC9D 7B CHRADR LD A,E


FC9E 0F RRCA


FC9F 0F RRCA


FCA0 0F RRCA


FCA1 E6E0 AND #E0


FCA3 82 ADD A,D


FCA4 6F LD L,A


FCA5 7B LD A,E


FCA6 E618 AND #18


FCA8 F640 OR #40


FCAA 67 LD H,A


FCAB C9 RET


;Find address of next line from address of present


FCAC 7C NXTLIN LD A,H


FCAD 0F RRCA


FCAE 0F RRCA


FCAF 0F RRCA


FCB0 C620 ADD A,#20


FCB2 3009 JR NC,DONE2


FCB4 67 LD H,A


FCB5 7D LD A,L


FCB6 C620 ADD A,#20


FCB8 6F LD L,A


FCB9 3001 JR NC,DONE1


FCBB 24 INC H


FCBC 7C DONE1 LD A,H


FCBD 07 DONE2 RLCA


FCBE 07 RLCA


FCBF 07 RLCA


FCC0 67 LD H,A


FCC1 C9 RET


;Variables


FCC2 00 DPOS DEFB 0 ;Down and across position


FCC3 00 APOS DEFB 0 ;of explosion on screen


FCC4 05 DLIM DEFB 5 ;Size of explosion


FCC5 20 ALIM DEFB 32 ;in character squares


FCC6 32 SPEED DEFB 50 ;Speed of explosion


FCC7 00 DONE DEFB 0 ;Flag to indicate end of explosion


FCC8 00 COUNT DEFB 0 ;Interrupts to go before next fade


FCC9 00 ROUND DEFB 0 ;Number of fades to go


!1.......^.........^.........^.........^........





!B


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from Your Spectrum #6 (Aug.1984)


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!$