Changes
<pre>
;; This example shows a simple raster using the CPC+
;; extended palette, and using standard CPC compatible
;; raster interrupts to define the position of the raster
;; on the display.
;;
;; This example is designed for CPC+ only and will
;; not work on CPC or KC Compact.
;;
;;
;; This example will compile with the MAXAM assembler
;; or the built-in assembler of WinAPE32.
;; NOTE - For this example to work, the code must not
;; be in the range &4000-&7fff inclusive. The ASIC registers
;; are paged into this range, and the code would not be
;; visible to the CPU if it was also in this range.
org &8000
.scr_set_mode equ &bc0e
;;--------------------------------------------------
;; clear screen
ld a,1
call scr_set_mode
;;--------------------------------------------------
;; STEP 1 - Unlock CPC+ additional features
;; unlock asic to gain access to asic registers
di
ld b,&bc
ld hl,sequence
ld e,17
.seq
ld a,(hl)
out (c),a
inc hl
dec e
jr nz,seq
ei
;;----------------------------------------------------------
;; STEP 2 - Install a interrupt handler
;;
;; install a interrupt handler
;; disable interrupts
di
;; interrupt mode 1 (call to interrupt handler at &0038)
im 1
;; &c9 corresponds to the opcode RET
;; &fb corresponds to the opcode EI
;;
;; RET opcode takes 3us, EI opcode takes 1us
;; write EI,RET to interrupt handler at &0038
ld hl,&c9fb
ld (&0038),hl
;; enable interrupts
ei
;;------------------------------------------------------------
.main_loop
;;---------------------------------------
;; wait for start of vsync
;;
;; at this point the code assumes the VSYNC is not active.
;;
;; this code waits for the VSYNC to change from inactive->active
;; which signals the start of the VSYNC.
;; PPI port B
ld b,&f5
.ml1
;; read input
in a,(c)
;; transfer bit 0 into carry
;; if bit 0=1 then VSYNC is active, if bit 0=0 then VSYNC is inactive
rra
jr nc,ml1
;;----------------------------------------
;; wait for interrupt
halt
;; wait for interrupt
halt
;; wait for interrupt
halt
;; wait for interrupt
halt
;; delay so that colour change position is not visible (hidden
;; by border and horizontal flyback)
defs 20
;; page-in asic registers to &4000-&7fff
ld bc,&7fb8 ;; [3]
out (c),c ;; [4]
ld de,&6400 ;; colour 0
;; start of table
ld hl,raster_colours
;; number of colours in table
ld b,end_raster_colours-raster_colours
;; /2
srl b
.rl
;; read colour from table (a byte at a time)
;; write colour to ASIC colour palette (a byte at a time)
ld a,(hl) ;; [2]
ld (de),a ;; [2]
inc hl ;; [2]
inc e ;; [1]
ld a,(hl) ;; [2]
ld (de),a ;; [2]
inc hl ;; [2]
dec e ;; [1]
;; delay so that the next colour change
;; occurs immediatly below this one
defs 64-2-2-2-1-2-2-2-1-1-3
dec b ;; [1]
jp nz,rl ;; [3]
;; page-out asic registers
ld bc,&7fa0
out (c),c
jp main_loop
;;---------------------------------------------
;; - there is two bytes per colour.
;; - these are stored in a form that can be written direct
;; to the CPC+ colour palette registers
;; e.g. xGRB
.raster_colours
defw &0111
defw &0222
defw &0333
defw &0444
defw &0555
defw &0666
defw &0777
defw &0888
defw &0999
defw &0aaa
defw &0bbb
defw &0ccc
defw &0ddd
defw &0eee
defw &0fff
defw &0fff
defw &0eee
defw &0ddd
defw &0ccc
defw &0bbb
defw &0aaa
defw &0999
defw &0888
defw &0777
defw &0666
defw &0555
defw &0444
defw &0333
defw &0222
defw &0111
defw &0000
.end_raster_colours
;;----------------------------------------------------------
;; this is the sequence to unlock the ASIC extra features
.sequence
defb &ff,&00,&ff,&77,&b3,&51,&a8,&d4,&62,&39,&9c,&46,&2b,&15,&8a,&cd,&ee
</pre>
[[Category:Programming]][[Category:CPC plus]]
;; This example shows a simple raster using the CPC+
;; extended palette, and using standard CPC compatible
;; raster interrupts to define the position of the raster
;; on the display.
;;
;; This example is designed for CPC+ only and will
;; not work on CPC or KC Compact.
;;
;;
;; This example will compile with the MAXAM assembler
;; or the built-in assembler of WinAPE32.
;; NOTE - For this example to work, the code must not
;; be in the range &4000-&7fff inclusive. The ASIC registers
;; are paged into this range, and the code would not be
;; visible to the CPU if it was also in this range.
org &8000
.scr_set_mode equ &bc0e
;;--------------------------------------------------
;; clear screen
ld a,1
call scr_set_mode
;;--------------------------------------------------
;; STEP 1 - Unlock CPC+ additional features
;; unlock asic to gain access to asic registers
di
ld b,&bc
ld hl,sequence
ld e,17
.seq
ld a,(hl)
out (c),a
inc hl
dec e
jr nz,seq
ei
;;----------------------------------------------------------
;; STEP 2 - Install a interrupt handler
;;
;; install a interrupt handler
;; disable interrupts
di
;; interrupt mode 1 (call to interrupt handler at &0038)
im 1
;; &c9 corresponds to the opcode RET
;; &fb corresponds to the opcode EI
;;
;; RET opcode takes 3us, EI opcode takes 1us
;; write EI,RET to interrupt handler at &0038
ld hl,&c9fb
ld (&0038),hl
;; enable interrupts
ei
;;------------------------------------------------------------
.main_loop
;;---------------------------------------
;; wait for start of vsync
;;
;; at this point the code assumes the VSYNC is not active.
;;
;; this code waits for the VSYNC to change from inactive->active
;; which signals the start of the VSYNC.
;; PPI port B
ld b,&f5
.ml1
;; read input
in a,(c)
;; transfer bit 0 into carry
;; if bit 0=1 then VSYNC is active, if bit 0=0 then VSYNC is inactive
rra
jr nc,ml1
;;----------------------------------------
;; wait for interrupt
halt
;; wait for interrupt
halt
;; wait for interrupt
halt
;; wait for interrupt
halt
;; delay so that colour change position is not visible (hidden
;; by border and horizontal flyback)
defs 20
;; page-in asic registers to &4000-&7fff
ld bc,&7fb8 ;; [3]
out (c),c ;; [4]
ld de,&6400 ;; colour 0
;; start of table
ld hl,raster_colours
;; number of colours in table
ld b,end_raster_colours-raster_colours
;; /2
srl b
.rl
;; read colour from table (a byte at a time)
;; write colour to ASIC colour palette (a byte at a time)
ld a,(hl) ;; [2]
ld (de),a ;; [2]
inc hl ;; [2]
inc e ;; [1]
ld a,(hl) ;; [2]
ld (de),a ;; [2]
inc hl ;; [2]
dec e ;; [1]
;; delay so that the next colour change
;; occurs immediatly below this one
defs 64-2-2-2-1-2-2-2-1-1-3
dec b ;; [1]
jp nz,rl ;; [3]
;; page-out asic registers
ld bc,&7fa0
out (c),c
jp main_loop
;;---------------------------------------------
;; - there is two bytes per colour.
;; - these are stored in a form that can be written direct
;; to the CPC+ colour palette registers
;; e.g. xGRB
.raster_colours
defw &0111
defw &0222
defw &0333
defw &0444
defw &0555
defw &0666
defw &0777
defw &0888
defw &0999
defw &0aaa
defw &0bbb
defw &0ccc
defw &0ddd
defw &0eee
defw &0fff
defw &0fff
defw &0eee
defw &0ddd
defw &0ccc
defw &0bbb
defw &0aaa
defw &0999
defw &0888
defw &0777
defw &0666
defw &0555
defw &0444
defw &0333
defw &0222
defw &0111
defw &0000
.end_raster_colours
;;----------------------------------------------------------
;; this is the sequence to unlock the ASIC extra features
.sequence
defb &ff,&00,&ff,&77,&b3,&51,&a8,&d4,&62,&39,&9c,&46,&2b,&15,&8a,&cd,&ee
</pre>
[[Category:Programming]][[Category:CPC plus]]
