Spectrum Computing

Code: Select all

  FONT EQU [your custom font address]

SCROLL:

  LD HL, TEXT

  LD (MESSAGE),HL    ; loads the text address in MESSAGE
  LD (L_35489),HL    ; points to the first character of the text
  
L_35387:  HALT
  CALL 00654                ; calls the control key routine
  INC E                     ; increases E by 1, if it's 255 (no key pressed) turns to 0
  RET NZ                     ; JP NZ, [address] to exit to a different memory location
  CALL L_35414
  JP L_35387
L_35413: DEC C
L_35414:  LD HL,20735       ; 20735 (default)
  PUSH HL
  LD B,008
L_35420:  PUSH BC
  PUSH HL
  LD B,032
  AND A
L_35425:  RL (HL)
  DEC L
  DJNZ L_35425
  POP HL
  INC H
  POP BC
  DJNZ L_35420
  LD HL,(L_35489)           ; get current place in the text
  LD L,(HL)                 ; get the letter 
  LD H,0  
  ADD HL,HL
  ADD HL,HL
  ADD HL,HL                 ; letter times 8
  LD DE,FONT-256            ; get font address ( don't forget its minus 256 -> 32*8 )
  ADD HL,DE                 ; HL now holds the address of the character in the font
  EX DE,HL                  ; exchange so DE is letter in memory we wish to use
  POP HL                    ; retrieve where on screen we are going to put this vertical line of pixels
  LD A,(PUNTO_A)
  LD C,A
  LD B,008
L_35459:  LD A,(DE)
  AND C
  JR Z,L_35464
  INC (HL)
L_35464:  INC H
  INC DE
  DJNZ L_35459
  LD HL,PUNTO_A
  RRC (HL)
  RET NC
  LD HL,(L_35489)
  INC HL
  LD A,(HL)
  AND A
  JR NZ,L_35485
  LD HL,(MESSAGE)
L_35485:  LD (L_35489),HL

   RET

L_35489: DEFS 2  
  
MESSAGE: DEFS 2

PUNTO_A:  ADD A,B 

TEXT:
  DEFM " Here goes your text."
  DEFM " Remember to put a space"
  DEFM " before every sentence, for better readability."