ZX Spectrum Next Samples

ctctest.asm

        SLDOPT COMMENT WPMEM, LOGPOINT, ASSERTION
        DEVICE ZXSPECTRUMNEXT
        CSPECTMAP "ctctest.map"

        org $8000

ctc0    equ $183b
main:
        nextreg 7,0     ; set speed

        di              ; disable interrupts

        nextreg $c0, (ivt & %11100000) | 1      ; setup vector table, enable Next IM2
        nextreg $c4, %00000000                  ; disable /INT and ULA interrupts
        nextreg $c5, %00000001                  ; enable CTC channel 0 interrupts, disable CTC channel 1-7 interrupts
        nextreg $c6, %00000000                  ; disable UART interrupts

        ld bc, ctc0             ; load CTC Channel 0 Port

        ld a, 1                 
        out (c), a              ; disable CTC Channel 0

        ld a, %10100101         ; enable intertupt, counter mode, 256 prescaler, 0,0,0, time const follows, reset, control word
        out (c), a              ; write control word to CTC Channel 0

        ld a, 249               ; time constant                               
        out (c), a              ; write time constant to CTC Channel 0

        ld a, high ivt          ; high byte of the interrupt vector table                
        ld i, a                 ; loaded into the I register

        im 2                    ; switch CPU to interrupt mode 2
        ei                      ; enable interrupts

        jr $                    ; loop forever

;------------------------------------------------------------------------------
; CTC Channel 0 Interrupt Handler
ctc0handler:
        push af                 ; Save AF
          ld a, (beeper)        ; Load current beeper and border value
          xor %00010000         ; Flip beeper bit
          ld (beeper), a        ; Store new beeper value
          out ($fe), a          ; Write new value to the IO Port
        pop af                  ; Restore AF

        ei                      ; Reenable interrupts
        reti                    ; Return from Interrupt
beeper  db %00000011            ; Default to beeper off and a magenta border

;------------------------------------------------------------------------------
; Default Interrupt Handler - Does nothing but reenable interrupts and return
; This is not called because all the associated interrupt have been disabled
inthandler:
        ei                      ; Reenable interrupts
        reti                    ; Return from Interrupt

;------------------------------------------------------------------------------
; Interupt Vector Table
        align 32
ivt:
        dw      inthandler      ; 0 - line interrupt
        dw      inthandler      ; 1 - uart0 rx
        dw      inthandler      ; 2 - uart1 rx
        dw      ctc0handler     ; 3 - ctc 0 <--- Our handler for the CTC Channel 0
        dw      inthandler      ; 4 - ctc 1
        dw      inthandler      ; 5 - ctc 2
        dw      inthandler      ; 6 - ctc 3
        dw      inthandler      ; 7 - ctc 4
        dw      inthandler      ; 8 - ctc 5
        dw      inthandler      ; 9 - ctc 6
        dw      inthandler      ; 10 - ctc 7
        dw      inthandler      ; 11 - ula
        dw      inthandler      ; 12 - uart0 tx
        dw      inthandler      ; 13 - uart1 tx
        dw      inthandler      ; 14
        dw      inthandler      ; 15

;------------------------------------------------------------------------------
; Stack reservation
STACK_SIZE      equ     100

stack_bottom:
        defs    STACK_SIZE * 2
stack_top:
        defw    0

;------------------------------------------------------------------------------
; Output configuration
        SAVENEX OPEN "ctctest.nex", main, stack_top 
        SAVENEX CORE 2,0,0
        SAVENEX CFG 7,0,0,0
        SAVENEX SCREEN SCR
        SAVENEX AUTO 
        SAVENEX CLOSE