The Little Mermaid:ROM map

From Data Crystal
Revision as of 18:15, 27 December 2018 by Dugongue (talk | contribs)
Jump to navigation Jump to search

Page 06 (0x8000-0xBFFF)

Address in ROM: 0x18010-0x1C00F

0x8000
Runs the action scripts of every object slot from lowest to highest and checks for collisions each frame.
06:8000:A5 B1     LDA $00B1   ; Check Ariel's health
06:8002:F0 3A     BEQ $803E   ; Exit if zero 
06:8004:A2 01     LDX #$01
06:8006:86 EF     STX $00EF   ; Current slot #
06:8008:A9 06     LDA #$06
06:800A:85 99     STA $0099   ; ?

06:800C:BD 00 03  LDA $0300,X 
06:800F:10 25     BPL $8036   ; Skip ahead if slot is empty
06:8011:BD A0 04  LDA $04A0,X ; Check if object is stunned
06:8014:D0 16     BNE $802C   ;  If so, skip action script

06:8016:BC 10 03  LDY $0310,X
06:8019:B9 20 85  LDA $8520,Y ; Obtain address of action script
06:801C:85 00     STA $0000   ;  from jump table located
06:801E:B9 80 85  LDA $8580,Y ;   at 0x8520,0x8580
06:8021:85 01     STA $0001
06:8023:A9 80     LDA #$80    ; Set return address
06:8025:48        PHA
06:8026:A9 2B     LDA #$2B
06:8028:48        PHA
06:8029:6C 00 00  JMP ($0000) ; Run object's action script

06:802C:E0 03     CPX #$03    ; Check if object is a bubble
06:802E:90 06     BCC $8036   ; Jump ahead if so
06:8030:20 3F 80  JSR $803F   ; Run action if object is colliding with Ariel
06:8033:20 FF 80  JSR $80FF   ; Run action if object is colliding with a bubble 

06:8036:E6 EF     INC $00EF   ; Tick up to next object slot
06:8038:A6 EF     LDX $00EF   
06:803A:E0 10     CPX #$10    ; Loop until all slots examined
06:803C:D0 CA     BNE $8008
06:803E:60        RTS -----------------------------------------

Page 07 (0xC000-0xFFFF)

Location in ROM: 0x1C010-0x2000F

0xC250
Advance random number generator each frame 
07:C250:A2 00     LDX #$00
07:C252:A0 04     LDY #$04
07:C254:B5 E4     LDA $E4,X
07:C256:29 02     AND #$02
07:C258:85 00     STA $0000
07:C25A:B5 E5     LDA $E5,X
07:C25C:29 02     AND #$02
07:C25E:45 00     EOR $0000 ; If 0x02 bits of 0xE4 and 0xE5
07:C260:18        CLC       ;  are the same, highest bit of
07:C261:F0 01     BEQ $C264 ;   new RNG value will be zero.
07:C263:38        SEC       ;    Otherwise, it will be one.
07:C264:76 E4     ROR $E4,X ;     Then shift all previous bits right.
07:C266:E8        INX
07:C267:88        DEY
07:C268:D0 FA     BNE $C264
07:C26A:60        RTS -----------------------------------------