Product specifications

;
;GRAFIK-CLEAR SCREEN USING PATTERN NUMBER 0
; DRAW BRODER USING PATTERN NUMBER 8
; FOR USE WITH GRAPHICS 1 MODE SCREEN
;
; ASSUMPTIONS DESCRIBED ABOVE
; ALSO ASSUME THAT VDP WRITE-ONLY REIGSTERS
; HAVE ALREADY BEEN SET-UP
;
; NO PARAMETERS REQUIRED ON ENTRY
; NO REGISTERS AFFECTED ON EXIT
;
GRAFIK: PUSH AF ;Save old Acc and flags
PUSH BC ;Save BC register pair
PUSH DE ;Save DE register pair
PUSH HL ;Save HL Register pair
CALL CLRSCR ;Clear the screen
CALL BORDER ;Draw the border
POP HL ;Get old HL register pair
POP DE ;Get old DE register pair
POP BC ;Get old BC register pair
POP AF ;Get old Acc and flags
RET ;Return to calling routine
;
CLRSCR: LD DE,£C00 ;Set the VDP write to VRAM
CALL VSETOT ;Pointer to the start of the
;graphics display screen
LD C,0 ;Load the clear screen character
;into the output register
LD HL,768 ;Loop counter – 768 (Decimal)
CALL OUTBLK ;This routine will output the byte
;held in C to VRAM from the start
;address held in DE HL number
;of times
RET ;Return to calling routine
;
BORDER: CALL TOP ;Draw the top of screen border
CALL BOTTOM ;Draw the bottom of screen border
CALL SIDES ;Draw a border down both sides
;of the graphics display screen
RET ;Return to the calling routine
;
TOP: LD DE,£C00 ;Set the VDP write to VRAM
CALL VSETOT ;pointer to the start of the top line
;of the graphics display screen area
LD C,8 ;Load the border character into
;the output register
LD HL,32 ;Loop counter = 32 (Decimal)
CALL OUTBLK ;This routine will output the byte
;held in C to VRAM from the start