View source for Programming:Next / previous line calculation

= 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

<pre>
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


</pre>

== Without Firmware ==

'''Input:''' HL=Address

'''Output:''' HL=Address of the next line

'''Destroyed:''' AF,BC

<pre>
; 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
</pre>

= 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

<pre>
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

</pre>



= Fastest way to print a character in Mode 2 =


'''Input:''' HL=Address  DE=screen address (works for every first line of screen !! For example: &C000, &C050, &C0A0 etc..)

'''Destroyed:''' AF, C

'''Unchanged:''' DE returns to its input value (through C register)

''''If HL is not page aligned, INC HL must be used instead of INC L (1 NOP SLOWER!)


<pre>
ld c,d
ld a,(hl):ld(de),a:inc l:set 3,d
ld a,(hl):ld(de),a:inc l:ld d,c:set 4,d
ld a,(hl):ld(de),a:inc l:set 3,d
ld a,(hl):ld(de),a:inc l:ld d,c:set 5,d
ld a,(hl):ld(de),a:inc l:set 3,d
ld a,(hl):ld(de),a:inc l:set 4,d:res 3,d
ld a,(hl):ld(de),a:inc l:set 3,d
ld a,(hl):ld(de),a
ld d,c

</pre>



[[Category:Programming]]