Routines
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E87C: Scroll the screen up 6 rows
Used by the routine at EC7B.
E87C LD HL,$E7EC Set the instruction at E7EB to 'LD BC,$0020'
E87F LD (HL),$20
E881 LD L,$EF Set the instruction at E7EE to 'LDIR'
E883 LD (HL),$B0
E885 LD B,$06 6 rows will be scrolled on
E887 PUSH BC Save the primary screen row counter
This entry point is used by the routine at FC6A.
E888 LD B,$13 There are 19 screen rows to move up
E88A LD DE,$5800 DE=destination attribute file address (top row)
E88D LD HL,$5820 HL=source attribute file address (second row from the top)
E890 PUSH BC Save the secondary screen row counter
E891 PUSH HL Save the source attribute file address
E892 PUSH DE Save the destination attribute file address
E893 CALL $E7E8 Move one screen row up
E896 POP HL HL=source attribute file address
E897 LD C,$20 Point HL at the next row down in the attribute file
E899 ADD HL,BC
E89A EX DE,HL Transfer this address to DE
E89B POP HL HL=destination attribute file address
E89C ADD HL,BC Point HL at the next row down in the attribute file
E89D POP BC Restore the secondary screen row counter to B
E89E DJNZ $E890 Jump back until all 19 screen rows have been moved up
E8A0 LD HL,$7FFF 7FFF holds the y-coordinate of the topmost row of the play area on screen
E8A3 INC (HL) Increment this
E8A4 LD HL,$131F L=31 (rightmost screen column), H=19 (bottom row of the screen)
E8A7 PUSH HL Save the screen coordinates briefly
E8A8 CALL $E70C Print a tile at screen coordinates (L,19)
E8AB POP HL Restore the screen coordinates to HL
E8AC DEC L Have we printed every tile in the row yet?
E8AD JP P,$E8A7 Jump back if not
E8B0 POP BC Restore the primary screen row counter to B
E8B1 DJNZ $E887 Jump back until 6 rows have been scrolled on
E8B3 RET
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