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;************************************************************************
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;************************************************************************
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;** An Assembly File Listing to generate a 16K ROM for the ZX Spectrum **
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;** An Assembly File Listing to generate a 16K ROM for the ZX Spectrum **
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;************************************************************************
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;************************************************************************
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;
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;
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; 03-13-2016:
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; Add custom NMI handler and a function to enter game pokes after pressing the NMI button
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;
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; 11-10-2014:
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; 11-10-2014:
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; This version has been updated to correctly handle the NMI jump.
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; This version has been updated to correctly handle the NMI jump.
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;
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;
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; -------------------------
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; -------------------------
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; Last updated: 13-DEC-2004
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; Last updated: 13-DEC-2004
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Line 252... |
; placing two zeros in the NMIADD system variable.
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; placing two zeros in the NMIADD system variable.
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;; RESET
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;; RESET
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L0066: PUSH AF ; save the
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L0066: PUSH AF ; save the
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PUSH HL ; registers.
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PUSH HL ; registers.
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LD HL,($5CB0) ; fetch the system variable NMIADD.
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; LD HL,($5CB0) ; fetch the system variable NMIADD.
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LD HL, nmi_handler ; Custom NMI handler
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LD A,H ; test address
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LD A,H ; test address
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OR L ; for zero.
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OR L ; for zero.
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; JR NZ,L0070 ; skip to NO-RESET if NOT ZERO
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; JR NZ,L0070 ; skip to NO-RESET if NOT ZERO
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JR Z,L0070 ; **FIXED**
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JR Z,L0070 ; **FIXED**
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; ---------------------
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; ---------------------
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;; spare
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;; spare
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L386E: DEFB $FF, $FF ;
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L386E: DEFB $FF, $FF ;
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; ----------------------------------------------------------------------------
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; This custom NMI handler provides a way to enter a POKE for a game by typing in
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; the address (5 decimal digits) followed by the value (3 decimal digits)
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; after which the value will be stored to the selected location.
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; ----------------------------------------------------------------------------
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nmi_handler: ; NMI handler
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push bc
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push de
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push ix
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ld hl,$04000 ; Use the screen memory as a temp storage
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ld e,$08 ; Will load 8 characters (numbers)
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next_key:
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ld bc,$f7fe ; Number row 1..5
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in a,(c)
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ld c,a
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ld a,$01 ; Preload "1"
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bit 0,c ; If the key has been pressed
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jr z,accept_key ; Accept it
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inc a ; Preload "2"
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bit 1,c ; and continue for every key up to "5"
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jr z,accept_key
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inc a
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bit 2,c
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jr z,accept_key
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inc a
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bit 3,c
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jr z,accept_key
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inc a
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bit 4,c
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jr z,accept_key
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ld bc,$effe ; Number row 6...0
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in a,(c)
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ld c,a
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ld a,$06
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bit 4,c
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jr z,accept_key
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inc a
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bit 3,c
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jr z,accept_key
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inc a
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bit 2,c
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jr z,accept_key
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inc a
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bit 1,c
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jr z,accept_key
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xor a
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bit 0,c
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jr z,accept_key
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jp next_key
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accept_key:
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ld (hl),a ; Store current key value into the buffer
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inc hl
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poll_key_release: ; Poll for any pressed key to be released
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ld bc,$f7fe
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in a,(c)
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cpl
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and $1f
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jr nz,poll_key_release
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ld bc,$effe
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in a,(c)
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cpl
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and $1f
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jr nz,poll_key_release
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dec e ; Decrement the number of keys expected
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jr nz,next_key ; Jump back to accept next key if not yet done
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ld ix,$4000
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ld b,$05 ; First 5 numbers represent the address to POKE to
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call decimal_to_hl
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push hl ; Address is in HL, store it
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ld b,$03 ; Next 3 numbers represent the value to POKE
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call decimal_to_hl
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ld a,l ; Value is in L
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pop hl ; Get the address
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ld (hl),a ; POKE a value
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pop ix
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pop de
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pop bc
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pop hl
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pop af
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retn
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; Read a decimal value pointed to by IX register
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; The number of digits is given in B register
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; Return the value in HL register
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decimal_to_hl:
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ld hl,$0000 ; Start with value of 0
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lp2:
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push bc
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ld b,$09 ; Multiply the current value by 10
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push hl
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pop de
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lp1:
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add hl,de
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djnz lp1
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pop bc
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ld e,(ix+0) ; Read in the next digit
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ld d,$00
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add hl,de ; Add in the new value
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inc ix
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djnz lp2 ; Loop for the requested number of digits
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ret
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DEFB $FF, $FF, $FF, $FF, $FF, $FF, $FF, $FF;
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DEFB $FF, $FF, $FF, $FF, $FF, $FF, $FF, $FF;
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DEFB $FF, $FF, $FF, $FF, $FF, $FF, $FF, $FF;
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DEFB $FF, $FF, $FF, $FF, $FF, $FF, $FF, $FF;
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DEFB $FF, $FF, $FF, $FF, $FF, $FF, $FF, $FF;
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DEFB $FF, $FF, $FF, $FF, $FF, $FF, $FF, $FF;
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DEFB $FF, $FF, $FF, $FF, $FF, $FF, $FF, $FF;
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DEFB $FF, $FF, $FF, $FF, $FF, $FF, $FF, $FF;
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