Programming:Next / previous line calculation
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Next line
This routines calculate the next line from the given address.
Firmware
Input: HL=Address
Output: HL=Address of the next line
Destroyed: AF
SCR_NEXT_LINE equ #BC26 call SCR_NEXT_LINE ACTUAL #BC26 ROUTINE FOLLOWS: ld a,h:add #08:ld h,a:and #38:ret nz ld a,h:sub #40:ld h,a:ld a,l:add reg1*2:ld l,a:ret nc ;reg1= CRTC reg.1 value inc h:ld a,h:and #07:ret nz ld a,h:sub #08:ld h,a:ret
Without Firmware
Input: HL=Address
Output: HL=Address of the next line
Destroyed: AF,BC
; Richard Fairhurst
; October 1997
;
;*** Next line down from HL ***
.nline ld a,8
add h
ld h,a
ret nc
ld bc,#c050
add hl,bc
ret
Previous line
This routines calculate the previous line from the given address.
Firmware
Input: HL=Address
Output: HL=Address of the previous line
Destroyed: AF
SCR_PREV_LINE equ #BC29 call SCR_PREV_LINE ACTUAL #BC29 ROUTINE FOLLOWS: ld a,h:sub #08:ld h,a:and #38:cp #38:ret nz ld a,h:add #40:ld h,a:ld a,l:sub reg1*2:ld l,a:ret nc ; reg1= CRTC reg.1 value ld a,h:dec h:and #07:ret nz ld a,h:add #08:ld h,a:ret
