Programming:Simple Raster Example 3 (uses CPC plus features)
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;; This example shows a simple raster using the CPC+
;; extended palette, and using the CPC+ programmable
;; raster interrupts to define the position of the raster
;; on the display.
;;
;; This example is designed for CPC+ only and will
;; not work on the CPC or KC Compact.
;;
;; This example will compile with the MAXAM assembler
;; or the built-in assembler of WinAPE32.
.scr_set_mode equ &bc0e
org &8000
nolist
;;--------------------------------------------------
;; clear screen
ld a,1
call scr_set_mode
;;--------------------------------------------------
;; STEP 1 - Unlock CPC+ additional features
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
;; 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
;;----------------------------------------------------------
;; STEP 3 - Initialise CPC+ Programmable Raster Interrupt
;; disable interrupts
di
;; page-in asic registers to &4000-&7fff
ld bc,&7fb8
out (c),c
ld a,100 ;; line 100
ld (&6800),a ;; set line
;; page-out asic registers
ld bc,&7fa0
out (c),c
;; enable interrupts
ei
;;------------------------------------------------------------
.main_loop
;; wait for interrupt
halt
;; delay so that colour change is hidden by border
defs 16
;; page-in asic registers to &4000-&7fff
ld bc,&7fb8 ;; [3]
out (c),c ;; [4]
;; address of pen 0 in CPC+ ASIC registers
ld de,&6400 ;; [3]
;; start of table
ld hl,raster_colours ;; [3]
;; number of colours in table*2
ld b,end_raster_colours-raster_colours ;; [2]
;; /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 colour change
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
.raster_colours
defw &0001
defw &0004
defw &0008
defw &000d
defw &000f
defw &000d
defw &0008
defw &0004
defw &0001
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