    ;; 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