.CR SCMP .TF INVADER2.HEX,INT ; .TF INVADER2.BIN,bin .LF INVADER2.LST ; ***************************************************************************** ; MK14 Space Invaders game ; Rev 2.0 ; Written by Ian Reynolds Dec 2022 for the SBASM 8060 assembler ; ; Requires continuous memory from 0x200 to 0x7FF and base RAM at 0xF00 ; INS8154 setup is specific to the RelView MK14 VDU module, so may need adjustment for operation with ; other MK14 VDU cards ; For correct operation the VDU TOPPAGE signal needs to be connected to PS1, to use 2 adjacent pages of video RAM ; ; You have 5 lives ; When you clear all invaders from the screen a new set of invaders appear ; Hitting an invader gets you 1 point, up to a maximum 999 points ; The invaders are rotated across the screen. After 14 rotations the invaders drop down a row ; ; Keys: 1 to move shooter left ; 2 to shoot a bullet ; 3 to move shooter right ; GO to restart game once all lives are used ; ; All characters on screen are defined by constants, so easy to customise ; ; Visit the UK Vintage Radio Forums, Vintage Computers, for updates ; ; https://www.vintage-radio.net/ My username is Realtime ; ; ***************************************************************************** ; CHANGE LOG V2 ; Title text changed to MK14 INVADERS V2 ; 3 digit points counter ; SCORE changed to HITS ; Bullet character changed from : to " ; Sound triggers added using INS8154 Port A for ; Invader hit, Shooter hit, Bullet fired and Invader move ; Abort key function removed to save space ;****************************************************************************** ;Game Constants DISPL .EQ 0x0200 ; Start of VDU frame store PROG .EQ 0x0400 ; Start of program memory VAR .EQ 0x0F20 ; Place variables in base RAM INS8154 .EQ 0x0800 ; MK14 I/O chip base address Port_A .EQ 0x20 ; INS8154 Port A Output register write address Port_B .EQ 0x21 ; INS8154 Port B Output register write address Char_Border .EQ 0x2D ; '-' Char_Space .EQ 0x20 ; ' ' Char_InvL .EQ 0x1C ; '\' Char_InvR .EQ 0x2F ; '/' Char_Shooter .EQ 0x01 ; 'A' Char_Bullet .EQ 0x22 ; '"' Char_Bomb .EQ 0x2A ; '*' Char_Block .EQ 0x23 ; '#' Shoot_Y .EQ DISPL/256+1 ; Lower page of video RAM Shoot_X_pos .EQ 0xD0 ; 3rd to last row Score_line .EQ 0xF0 ; Last row Title_line .EQ 0x10 ; Top row above border Block_L .EQ 0x61 ; Low byte of position of Blocks Block_H .EQ DISPL/256+1 ; High byte of position of Blocks ; Game Variables Shoot_X .EQ 0x00 ; x-address of shooter (0x0-0xF) Bullet_X .EQ 0x01 ; x-position of the bullet Bullet_Y .EQ 0x02 ; y-position of the bullet Bullet_ON .EQ 0x03 ; non-zero if bullet is active Bomb_X .EQ 0x04 ; x-position of bomb Bomb_Y .EQ 0x05 ; y-position of bomb Bomb_ON .EQ 0x06 ; non-zero if bomb is active Game_over .EQ 0x07 ; non-zero if game over Lives .EQ 0x08 ; number of shooter lives left Points_L .EQ 0x09 ; Points counter Low byte (BCD) Points_H .EQ 0x0A ; Points counter High byte (BCD) Rot_loops .EQ 0x0B ; Count down. When zero the invaders are rotated left Drop_row .EQ 0x0C ; Count down. When zero the invaders can be dropped down one row Inv_row1L .EQ 0x0D ; Address of first row of invaders Inv_row1H .EQ 0x0E ; Address of first row of invaders Inv_row2L .EQ 0x0F ; Address of second row of invaders Inv_row2H .EQ 0x10 ; Address of second row of invaders Inv_row3L .EQ 0x11 ; Address of second row of invaders Inv_row3H .EQ 0x12 ; Address of second row of invaders Count1 .EQ 0x13 ; General purpose loop counter Count2 .EQ 0x14 ; General purpose loop counter Det_Inv .EQ 0x15 ; Non-zero when invaders detected on screen Ret_H .EQ 0x16 ; High byte of return-to-monitor address (ABORT) Ret_L .EQ 0x17 ; Low byte of return-to-monitor address (ABORT) Sound1 .EQ 0x18 ; Holds the latest sound event Sound2 .EQ 0x19 ; Pulse extender for sound event ; **************************************************************************** .OR PROG ENTER: LDI VAR/256 XPAH P2 LDI VAR\256 XPAL P2 ; XPAH P3 ; Store return to monitor address - ABORT function removed to save code space ; ST Ret_H(P2) ; XPAL P3 ; ST Ret_L(P2) ; Set up INS8154 ; The following assumes the RealView MK14 VDU is being used, with INS8154 Port B ; Other VDU's may require different set up byte LDI INS8154/256 ; Base address of I/O device XPAH P3 LDI INS8154\256 XPAL P3 LDI 0x0F ; ST 0x22(P3) ; Port A output definition register, bit7-bit4 inputs, bit3 to bit0 outputs LDI 0x08 ; ST 0x23(P3) ; Port B output definition register - bit3 (VDUOFF) as output, all others as inputs LDI 0x00 ST Port_A(P3) ; Initialise port A - all off (Port A defaults to basic I/O mode after a reset) LDI 0xF7 ; Set VDU control bits - Enable VDU only. All other controls are via RealView DIP switches ST Port_B(P3) ; Set port B outputs (Port B is always in basic I/O mode) ; ; Port A Sound Event Bits (all active low for aprox 150ms) ; Bit 0: Shooter fired bullet ; Bit 1: Invader hit ; Bit 2: Shooter killed ; Bit 3: Invaders move sideways ; ; Port B is set to all bits logic '1' except VDUOFF ; DIP switches to be used to set VDU configuration ; SW1: OFF (PS1 = logic 1) ; SW2: OFF (PS2 = logic 1) ; SW3: ON (PS3 = logic 0) ; SW4: ON (PS4 = logic 0) ; SW5: OFF (VDUOFF = 1. This allows the 8154 to control VDUOFF, wich is needed for the fast loader) ; SW6: ON (GR/nChar = 0) ; SW7: OFF (REVPAGES = 1) ; SW8: ON (INVERT = 0) ; SW9: ON (SRAM Enabled) ; SW10: ON (TOPPAGE connected to PS1) ; Port B bit 7 = PS3 - set to '1' \ ; Port B bit 6 = PS1 - set to '1' \ Sets the video RAM address ; Port B bit 5 = PS2 - set to '1' / PS1 must be logic '1' to allow it to be controlled by the TOPPAGE signal ; Port B bit 4 = PS4 - set to '1' / ; Port B bit 3 = VDUOFF - set to '0' for VDU on ; Port B bit 2 = Graphics/nCharacters - set to '1' for character mode ; Port B bit 1 = REVPAGES - set to '1' for 0x200 at top of the screen (0x300 at bottom) ; Port B bit 0 = INVERT - set to '1' for white on black video ; LDI 0x00 ; or lower FLAG2 for other card designs ; CAS START: ; These variables get set only for first round of a game LDI 0x00 ST Points_L(P2) ; Zero points ST Points_H(P2) ST Game_over(P2) ; Game not over LDI 0x05 ; ************************************************************* ST Lives(P2) ; Five shooter lives ST Shoot_X(P2) ; Place shooter at left middle of screen LDI 0x40 ST Inv_row1L(P2) ; Set display position for 1st row of invaders LDI 0x60 ST Inv_row2L(P2) ; Set display position for 2nd row of invaders LDI 0x80 ST Inv_row3L(P2) ; Set display position for 3rd row of invaders LDI DISPL/256 ST Inv_row1H(P2) ; Place all invaders in top half of screen ST Inv_row2H(P2) ST Inv_row3H(P2) INVADE: ;================================================ ; Create the start-up screen ;================================================ ; Fill display with spaces LDI DISPL/256 ; lower display memory page high byte XPAH P1 LDI DISPL\256 ; lower display memory page low byte XPAL P1 ; P1 now points to start of display SC1: LDI Char_Space ; space character to clear screen ST @1(P1) ; store and auto increment by 1 XPAH P1 XRI DISPL/256+2 ; XOR for comparison JZ SC2 ; Is P1_H equal to (Display Start + 2x256)? if yes then finished clearing RAM XRI DISPL/256+2 ; Restore P1_H XPAH P1 JMP SC1 ; Fill the third line (using P1) of display with '-' ; Fill the 2nd to last line (using P2) of display with '-' SC2: LDI DISPL/256 XPAH P1 LDI 0x20 XPAL P1 ; P1 contains start address of 2nd display row LDI DISPL/256+1 XPAH P3 LDI Shoot_X_pos+0x10 XPAL P3 ; P2 contains start address of 2nd to last display row SC3: LDI Char_Border ; upper and lower boarder character ST @1(P1) ST @1(P3) XPAL P1 XRI 0x30 ; XOR for comparison of 16 characters placed (P1_L started at 0x20) JZ SC4 ; Is P1_L equal to 0x10? if yes then finished border rows XRI 0x30 ; Restore P1_L XPAL P1 JMP SC3 ; Draw the protection blocks SC4: LDI Block_H ; Top Of Blocks XPAH P1 LDI Block_L XPAL P1 LDI 0x03 ; 3 rows of block ST Count1(P2) SC5: LDI 0x03 ST Count2(P2) ; 3 blocks per line SC6: LDI Char_Block ; Block # ST @1(P1) ; 3 characters wide ST @1(P1) ST @1(P1) LD @2(P1) ; 2 spaces DLD Count2(P2) JNZ SC6 LD @0x11(P1) ; jump a display line DLD Count1(P2) JNZ SC5 ; Draw the Invaders LD Inv_row1H(P2) ; Top Of invaders XPAH P1 LD Inv_row1L(P2) XPAL P1 LDI 0x03 ; 3 rows of invaders ST Count1(P2) SC7: LDI 0x04 ST Count2(P2) SC8: LDI Char_InvL ST @0x01(P1) LDI Char_InvR ST @0x03(P1) DLD Count2(P2) JNZ SC8 SC9: LD @0x10(P1) ; Move screen position on 20 bytes DLD Count1(P2) JNZ SC7 ; repeat ; Place the shooter LDI Shoot_X_pos OR Shoot_X(P2) ; move shooter to middle of line XPAL P1 LDI Shoot_Y XPAH P1 LDI Char_Shooter ST (P1) ; display shooter ; Output Title text SC11: LDI Title_text/256 ; Get start address of Title text block XPAH P3 LDI Title_text\256 XPAL P3 LDI DISPL/256 XPAH P1 LDI Title_line XPAL P1 LDI 0x02 ST Count2(P2) SC12: LD @1(P3) JZ SC13 ST @1(P1) ; copy it to screen JMP SC12 ;Output score line text SC13: LDI DISPL/256+1 XPAH P1 LDI Score_line XPAL P1 ; Set pointer to last line of display DLD Count2(P2) JNZ SC12 ;================================================ ; Initialise variables for each round of the game ;================================================ LDI 0x00 ST Sound1(P2) ; Clear any sound events ST Bullet_ON(P2) ; Bullet not active ST Bomb_ON(P2) ; Bomb not active LDI Shoot_Y ; Initial offset for bullet firing ST Bullet_Y(P2) LDI 0x0E ST Det_Inv(P2) ; Reset invaders on screen flag (any non zero value) ST Rot_loops(P2) ; Number of game loops before invaders are rotated ST Drop_row(P2) ; Number of rotates before invaders drop down a row LDI 0xC9 ST Bullet_X(P2) ; Initial X position of bullet ; Bomb_X, Bomb_Y, Rot_bytes, Count1, Count2 get initialised elsewhere on first use ;================================================ ; MAIN GAME LOOP ;================================================ ; Fire bullet upwards ;================================================ FB0: LD Bullet_ON(P2) JZ FB_EXIT LD Bullet_Y(P2) ; get display position of Bullet XPAH P1 LD Bullet_X(P2) XPAL P1 LD (P1) ; get character from display RAM at bullet position (before bullet gets displayed) XRI Char_Space ; is it a space (background)? JNZ FB1 LDI Char_Bullet ; Place bullet character on screen ST (P1) LDI Char_Space ST 0x10(P1) ; replace previous position with a space LD Bullet_X(P2) ; Get position of bullet XPAL P3 LD Bullet_Y(P2) XPAH P3 LD @-0x10(P3) ; Move position to the next row above XPAH P3 ; and store ST Bullet_Y(P2) XPAL P3 ST Bullet_X(P2) JMP FB_EXIT FB1: LD (P1) ; get character from display RAM at bullet position XRI Char_Block ; is it part of the defences? JZ FB_END LD (P1) ; get character from display RAM at bullet position XRI Char_InvL ; is it an invader? JNZ FB2 LDI Char_Space ST 0x01(P1) ; clear one character to right of bullet position JMP FB22 FB2: LD (P1) ; get character from display RAM at bullet position XRI Char_InvR ; is it an invader? JNZ FB3 LDI Char_Space ST -1(P1) ; clear one character to left of bullet position FB22: LDI 0x02 ST Sound1(P2) ; Store invader hit sound event (0x02) LD Points_L(P2) ; Increment points CCL DAI 0x01 ; Decimal add - i.e. BCD counter ST Points_L(P2) JNZ FB_END ILD Points_H(P2) ; Increment high points (no upper limit check to save space) JMP FB_END FB3: ; Uncomment next 3 lines for bullet to get destroyed by collision with a bomb LD (P1) ; get character from display RAM at bullet position XRI Char_Bomb ; is it a bomb? JZ FB_END FB4: LD (P1) XRI Char_Border ; Has it reached the top of screen JNZ FB_EXIT LDI Char_Space ST 0x10(P1) ; clear previous bullet position JMP BULLET_OFF FB_END: LDI Char_Space ST (P1) ; clear screen at bullet position ST 0x10(P1) ; replace previous position with a space BULLET_OFF: LDI 0x00 ST Bullet_ON(P2) ; Set bullet to inactive LDI 0xC7 ST Bullet_X(P2) ; Set initial offset for bullet firing LDI Shoot_Y ST Bullet_Y(P2) FB_EXIT: ;================================================ ; Move the shooter ;================================================ LDI Shoot_Y ; Determine where Shooter should be XPAH P1 LD Shoot_X(P2) ORI Shoot_X_pos XPAL P1 LDI Char_Shooter ST (P1) ; Place the shooter LDI Char_Space ST -1(P1) ; clear to left of shooter to overwrite old position LD Shoot_X(P2) XRI 0x0F JZ DB0 ; If shooter is not at far right then clear to right to overwrite old position LDI Char_Space ST 1(P1) ;================================================ ; Drop Bomb ;================================================ DB0: LD Bomb_ON(P2) JZ DB_EXIT LD Bomb_Y(P2) ; get display position of Bomb XPAH P1 LD Bomb_X(P2) XPAL P1 LD (P1) ; get character from display RAM at bomb position (before bomb gets displayed) XRI Char_Space ; is it a space (background)? JNZ DB1 LDI Char_Bomb ST (P1) ; Place Bomb on screen LDI Char_Space ST -0x10(P1) ; Clear previous position LD Bomb_X(P2) XPAL P3 LD Bomb_Y(P2) XPAH P3 LD @0x10(P3) ; Move position of Bomb to the next row XPAH P3 ST Bomb_Y(P2) XPAL P3 ST Bomb_X(P2) JMP DB_EXIT DB1: LD (P1) ; get character from display RAM at Bomb position XRI Char_Block ; is it part of the defences? JZ DB_END DB3: LD (P1) ; get character from display RAM at Bomb position XRI Char_Shooter ; is it the shooter? JNZ DB4 LDI 0x04 ST Sound1(P2) ; Shooter killed sound event (0x04) DLD Lives(P2) ; Decrement number of Lives JNZ DB_END ; If lives=0 then game over LDI 0x01 ST Game_over(P2) ; Set game over JMP BOMB_OFF DB4: ; Uncomment next 3 lines for bomb to get destroyed by collision with a bullet LD (P1) ; get character from display RAM at Bomb position XRI Char_Bullet ; is it a bullet? JZ DB_END DB5: LD (P1) XRI Char_Border ; has the bomb reached the bottom of screen? JNZ DB_EXIT LDI Char_Space ST -0x10(P1) ; Clear previous position JMP BOMB_OFF DB_END: LDI Char_Space ST (P1) ; Clear Bomb from screen ST -0x10(P1) BOMB_OFF: LDI 0x00 ST Bomb_ON(P2) ; Set Bomb to inactive DB_EXIT: ;================================================ ; Display Lives and Hits (3 nibbles) ;================================================ LDI Shoot_Y ; Determine position of score line on display XPAH P1 LDI Score_line+0x06 XPAL P1 LD Lives(P2) ; Get Lives ADI 0x30 ; Convert to number character ST @0x09(P1) ; Display Lives and move P1 to Points position LD Points_L(P2) ; Get points lower byte (BCD counter) ANI 0x0F ; Mask off lower nibble ADI 0x30 ; Convert to number character ST (P1) ; Display number and increment pointer LD Points_L(P2) ; Reload points lower byte ANI 0xF0 ; Mask off upper nibble SR ; Shift right 4 times SR SR SR ADI 0x30 ; Convert to number character ST -1(P1) ; Display number LD Points_H(P2) ; Get high byte ANI 0x0F ; Mask lower nibble ADI 0x30 ; Convert to number character ST -2(P1) ; Dislay number ;================================================ ; Scan upwards for an invader above shooter X position and enable drop bomb ;================================================ LD Bomb_ON(P2) ; if Bomb already dispatched then exit JNZ SU_EXIT LD Shoot_X(P2) ; get position of shooter XPAL P1 LDI Shoot_Y XPAH P1 SU0: LD (P1) ; get character from display RAM at scan position XRI Char_InvL ; is it an invader? JZ SU1 LD (P1) ; get character from display RAM at scan position XRI Char_InvR ; is it an invader JZ SU1 LD (P1) ; get character from display RAM at scan position XRI Char_Border ; has the scan reached the top of the display? If yes, exit as no invader found above the shooter JZ SU_EXIT LD @-0x10(P1) ; decrement to the next row above and repeat JMP SU0 SU1: LD @0x20(P1) ; move down 2 rows XPAH P1 ; Align bomb release position with detected invader ST Bomb_Y(P2) XPAL P1 ST Bomb_X(P2) LDI 0x01 ST Bomb_ON(P2) ; Enable bomb drop SU_EXIT: ;================================================ ; Check if game is over, otherwise rotate each row of invaders ;================================================ LD Game_over(P2) JNZ RT1 ; IF not zero then game over so don't move the invaders DLD Rot_loops(P2) JZ RT2 ; IF rotation loop counter not zero then don't move the invaders RT1: JS P3,RT10 ; Use JS as a long jump to RT10. There is no return from RT10 RT2: LD Bullet_ON(P2) ; If the bullet is enabled then blank it while rotating JZ RT3 LD Bullet_Y(P2) XPAH P1 LD Bullet_X(P2) XPAL P1 LDI Char_Space ST 0x10(P1) RT3: LD Bomb_ON(P2) ; If the Bomb is enabled then blank it while rotating JZ RT4 LD Bomb_Y(P2) XPAH P1 LD Bomb_X(P2) XPAL P1 LDI Char_Space ST -0x10(P1) RT4: LDI 0x0E ST Rot_loops(P2) ; Re-initialise the rotation counter ; check if any invaders left on screen LDI 0x00 ; Reset Invaders detected flag (zero means none detected) ST Det_Inv(P2) LDI 0x60 ; The complete set of invaders spans 0x60 locations on the display ST Count1(P2) ; initialise counter LD Inv_row3H(P2) XPAH P1 LD Inv_row3L(P2) ORI 0x0F ; P1 now points to last position in last row of invaders XPAL P1 RT5: LD (P1) ; Determine if any of the 0x60 locations contain an invader character XRI Char_InvL JZ RT6 LD @-1(P1) XRI Char_InvR JNZ RT7 RT6: LDI 0x01 ; Invaders detected ST Det_Inv(P2) ; The result in Det_Inv will be 0x01 if any invaders are on screen RT7: DLD count1(P2) JNZ RT5 ; Rotate all rows LDI 0x08 ST Sound1(P2) ; Store Invaders moving sound event (0x08) LD Inv_row1L(P2) ; Each row of invaders has it's own pointer register defining where it is on screen XPAL P1 LD Inv_row1H(P2) XPAH P1 JS P3,SFT_L ; Rotate row 1 LD Inv_row2L(P2) XPAL P1 LD Inv_row2H(P2) XPAH P1 JS P3,SFT_L ; Rotate row 2 LD Inv_row3L(P2) XPAL P1 LD Inv_row3H(P2) XPAH P1 JS P3,SFT_L ; Rotate row 3 ;================================================ ; Move invaders down one row ;================================================ DLD Drop_row(P2) ; Decrment loop counter JNZ RT10 ; If count is zero then drop invaders down a row, else exit LD Inv_row1H(P2) ; Check if invaders have reached low threshold XRI DISPL/256 JNZ RT8 LD Inv_row1L(P2) ANI 0xE0 XRI 0xE0 JNZ RT8 ; Jump to drop function JMP RT10 ; If Invader top row is at 0x02Ex then don't drop down any more RT8: LDI 0x0B ST Drop_row(P2) ; Reset the drop loop counter LDI 0x60 ; The complete set of invaders spans 0x60 locations on the display ST Count1(P2) ; initialise counter LD Inv_row3H(P2) XPAH P1 LD Inv_row3L(P2) ORI 0x0F ; P1 points to last position in last row of invaders XPAL P1 RT9: LD (P1) ; Move display block down one row (0x10 locations) ST 0x10(P1) LD @-1(P1) DLD count1(P2) JNZ RT9 LD Inv_row1H(P2) ; Increment row 1 pointer by 0x10 locations XPAH P3 LD Inv_row1L(P2) XPAL P3 LD @0x10(P3) XPAL P3 ST Inv_row1L(P2) XPAH P3 ST Inv_row1H(P2) LD Inv_row2H(P2) ; Increment row 2 pointer by 0x10 locations XPAH P3 LD Inv_row2L(P2) XPAL P3 LD @0x10(P3) XPAL P3 ST Inv_row2L(P2) XPAH P3 ST Inv_row2H(P2) LD Inv_row3H(P2) ; Increment row 3 pointer by 0x10 locations XPAH P3 LD Inv_row3L(P2) XPAL P3 LD @0x10(P3) XPAL P3 ST Inv_row3L(P2) XPAH P3 ST Inv_row3H(P2) ;================================================ ; Jump to reload start screen and continue with game if all invaders have been cleared ;================================================ RT10: LD Det_Inv(P2) ; Check if any invaders detected on screen (non zero) JNZ G_OVER JS P3,INVADE ; JS used as a long jump. No return from INVADE ;================================================ ; Check game over flag ;================================================ G_OVER: LD Game_over(P2) ; If flag set then game is over (Lives=0) JZ KBD ; Otherwise scan the keyboard LDI 0x00 ; Set Bullet and Bomb off ST Bullet_ON(P2) ST Bomb_ON(P2) ; Output game-_ed text GO0: LDI End_text/256 ; Get start address of Game Over text XPAH P3 LDI End_text\256 XPAL P3 LDI DISPL/256 XPAH P1 LDI 0xE3 XPAL P1 GO1: LD @1(P3) ; copy it to screen JZ KBD ST @1(P1) JMP GO1 ;================================================ ; scan keyboard for 1,2,3, GO, (ABORT disabled to save code space) ;================================================ KBD: LDI 0x0D ; point to MK14 display/keyboard XPAH P3 LDI 0x00 XPAL P3 LDI 0x00 ST (P3) ; Set all display segments to off LD Game_over(P2) ; If Game over flag is set then only test GO and ABORT keys JNZ TEST_GO TEST_1: ; Move shooter left LD 1(P3) ; read keypad 0x0D01 (Key 1) ORI 0x0F ; Mask top 4 bits XRI 0x7F ; Result will be zero if key pressed JNZ TEST_2 LD Shoot_X(P2) ; get current shooter position JZ TEST_2 ; If it's already zero then can't move left DLD Shoot_X(P2) TEST_2: ; Shoot bullet LD 2(P3) ; read keypad 0x0D02 (Key 2) ORI 0x0F ; Mask top 4 bits XRI 0x7F ; Result will be zero if key pressed JNZ TEST_3 LD Bullet_ON(P2) ; if bullet already in action then ignore key press JNZ TEST_3 LDI 0x01 ST Bullet_ON(P2) ; set bullet active ST Sound1(P2) ; Bullet fired sound stored (0x01) LD Bullet_X(P2) ; Set bullet release position to Shooter X position ANI 0xF0 ; Keep top 4 bits that define the row XOR Shoot_X(P2) ; add current shooter X position ST Bullet_X(P2) ; update position TEST_3: ; Move shooter right LD 3(P3) ; read keypad 0x0D03 (Key 3) ORI 0x0F ; Mask top 4 bits XRI 0x7F ; Result will be zero if key pressed JNZ TEST_ABORT LD Shoot_X(P2) ; get current shooter position XRI 0x0F JZ TEST_ABORT ; If it's already 15 then can't move right ILD Shoot_X(P2) TEST_GO: ; New Game LD 2(P3) ; read keypad 0x0D02 (Key GO) ORI 0x0F ; Mask top 4 bits XRI 0xDF ; Result will be zero if key pressed JNZ TEST_ABORT JS P3,START ; Use JS as a long jump to START, to restart the game TEST_ABORT: ; Abort to Monitor *** commented out to free up some space *** ; LD 4(P3) ; read keypad 0x0D04 (Key ABORT) ; ORI 0x0F ; Mask top 4 bits ; XRI 0xDF ; Result will be zero if key pressed ; JNZ SND_EV ; LD Ret_H(P2) ; Reinstate the monitor entry point ; XPAH P3 ; LD Ret_L(P2) ; XPAL P3 ; XPPC P3 ; return to the monitor ; Delay and generate sound event output SND_EV: LDI INS8154/256 XPAH P3 LDI INS8154\256 XPAL P3 LD Sound1(P2) ; Get current sound event OR Sound2(P2) ; extend pulse to 140ms (2 game cycles) XRI 0x0F ; invert to provide active low sound event strobes ST Port_A(P3) ; output on Port A LD Sound1(P2) ; Get current sound event ST Sound2(P2) ; store in sound 2 for pulse extension LDI 0x00 ST Sound1(P2) ; Reset sound event DLY 0x80 ; Main game loop-delay JS P3,FB0 ; Use JS as a long jump to FB0, the main loop ;================================================ ; Subroutine to shift left a row of invaders, twice ;================================================ SFT_L: LDI 0x02 ; Do it twice to avoid half an invader being displayed ST Count1(P2) SL1: LDI 0x0F ; 15 lcoations rotated left ... ST Count2(P2) LD (P1) XAE ; with the 16th location temporarily stored in the Extension register SL2: LD 1(P1) ; Do the rotate ST @1(P1) DLD Count2(P2) JNZ SL2 XAE ; place 16th postion ST (P1) LD @-0x0F(P1) DLD Count1(P2) JNZ SL1 RET P3 ;================================================ ; Lines of Text for writing to display. EOL is 0x00 ;================================================ Title_text .DB 0x0D,0x0B,0x31,0x34,0x20,0x09,0x0E,0x16,0x01,0x04,0x05,0x12,0x13,0x20,0x16,0x32,0x00 ; MK14 INVADERS V2 Score_text .DB 0x0C,0x09,0x16,0x05,0x13,0x3A,0x20,0x20,0x08,0x09,0x14,0x13,0x3A,0x00 ; LIVES: HITS: End_text .DB 0x20,0x10,0x12,0x05,0x13,0x13,0x20,0x07,0x0F,0x20,0x00 ; PRESS GO ; End_text .DB 0x07,0x01,0x0D,0x05,0x20,0x0F,0x16,0x05,0x12,0x20,0x20,0x20,0x20,0x20 ; GAME OVER ; Go_text .DB 0x20,0x20,0x10,0x12,0x05,0x13,0x13,0x20,0x07,0x0F,0x20,0x00 ; PRESS GO