;	
;	The WOZ Monitor for the Apple 1
;		Written by Steve Wozniak in 1976
;	
;	Ported for my online 6502 emulator
;	


; Page 0 Variables

	XAML			= $24		; Last "opened" location Low
	XAMH			= $25		; Last "opened" location High
	STL				= $26		; Store address Low
	STH				= $27		; Store address High
	L				= $28		; Hex value parsing Low
	H				= $29		; Hex value parsing High
	YSAV			= $2A		; Used to see if hex value is given
	MODE			= $2B		; $00=XAM, $7F=STOR, $AE=BLOCK XAM


; Other Variables

	IN				= $0200		; Input buffer to $027F
	KBD				= $FF00		; Console keyboard input
	DSP				= $FF00		; Console display output

		.WORD	$FE00
		.ORG	$FE00

RESET:			CLD				; Clear decimal arithmetic mode.
				CLI

NOTCR:			CMP #$88		; "_"? (Changed to BS)
				BEQ BACKSPACE	; Yes.
				CMP #$9B		; ESC?
				BEQ ESCAPE		; Yes.
				INY				; Advance text index.
				BPL NEXTCHAR	; Auto ESC if > 127.

ESCAPE:			LDA #'\'+$80	; "\".
				JSR ECHO		; Output it.

GETLINE:		LDA #$8A		; CR. (Changed to LF)
				JSR ECHO		; Output it.
				LDY #$01		; Initialize text index.

BACKSPACE:		DEY				; Back up text index.
				BMI GETLINE		; Beyond start of line, reinitialize.

NEXTCHAR:		LDA KBD			; Key ready?
				BMI NEXTCHAR	; Loop until ready.
				ORA #$80		; Add high bit for compat
				STA IN,Y		; Add to text buffer.
				JSR ECHO		; Display character.
				CMP #$8A		; CR? (Changed to LF)
				BNE NOTCR		; No.
				LDY #$FF		; Reset text index.
				LDA #$00		; For XAM mode.
				TAX				; 0->X.

SETSTOR:		ASL				; Leaves $7B if setting STOR mode.

SETMODE:		STA MODE		; $00=XAM, $7B=STOR, $AE=BLOCK XAM.

BLSKIP:			INY				; Advance text index.

NEXTITEM:		LDA IN,Y		; Get character.
				CMP #$8A		; CR? (Changed to LF)
				BEQ GETLINE		; Yes, done this line.
				CMP #'.'+$80	; "."?
				BCC BLSKIP		; Skip delimiter.
				BEQ SETMODE		; Set BLOCK XAM mode.
				CMP #':'+$80	; ":"?
				BEQ SETSTOR		; Yes. Set STOR mode.
				CMP #'R'+$80	; "R"?
				BEQ RUN			; Yes. Run user program.
				STX L			; $00->L.
				STX H			;	and H.
				STY YSAV		; Save Y for comparison.

NEXTHEX:		LDA IN,Y		; Get character for hex test.
				EOR #$B0		; Map digits to $0-9.
				CMP #$0A		; Digit?
				BCC DIG			; Yes.
				ADC #$88		; Map letter "A"-"F" to $FA-FF.
				CMP #$FA		; Hex letter?
				BCC NOTHEX		; No, character not hex.

DIG:			ASL
				ASL				; Hex digit to MSD of A.
				ASL
				ASL
				LDX #$04		; Shift count.

HEXSHIFT:		ASL				; Hex digit left, MSB to carry.
				ROL L			; Rotate into LSD.
				ROL H			; Rotate into MSD’s.
				DEX				; Done 4 shifts?
				BNE HEXSHIFT	; No, loop.
				INY				; Advance text index.
				BNE NEXTHEX		; Always taken. Check next character for hex.

NOTHEX:			CPY YSAV		; Check if L, H empty (no hex digits).
				BEQ ESCAPE		; Yes, generate ESC sequence.
				BIT MODE		; Test MODE byte.
				BVC NOTSTOR		; B6=0 STOR, 1 for XAM and BLOCK XAM
				LDA L			; LSD’s of hex data.
				STA (STL,X)		; Store at current ‘store index’.
				INC STL			; Increment store index.
				BNE NEXTITEM	; Get next item. (no carry).
				INC STH			; Add carry to ‘store index’ high order.

TONEXTITEM:		JMP NEXTITEM	; Get next command item.

RUN:			JMP (XAML)		; Run at current XAM index.

NOTSTOR:		BMI XAMNEXT		; B7=0 for XAM, 1 for BLOCK XAM.
				LDX #$02		; Byte count.

SETADR:			LDA L-1,X		; Copy hex data to
				STA STL-1,X		;	‘store index’.
				STA XAML-1,X	; And to ‘XAM index’.
				DEX				; Next of 2 bytes.
				BNE SETADR		; Loop unless X=0.

NXTPRNT:		BNE PRDATA		; NE means no address to print.
				LDA #$8A		; CR. (Changed to LF)
				JSR ECHO		; Output it.
				LDA XAMH		; ‘Examine index’ high-order byte.
				JSR PRBYTE		; Output it in hex format.
				LDA XAML		; Low-order ‘examine index’ byte.
				JSR PRBYTE		; Output it in hex format.
				LDA #':'+$80	; ":".
				JSR ECHO		; Output it.

PRDATA:			LDA #$A0		; Blank.
				JSR ECHO		; Output it.
				LDA (XAML,X)	; Get data byte at ‘examine index’.
				JSR PRBYTE		; Output it in hex format.

XAMNEXT:		STX MODE		; 0->MODE (XAM mode).
				LDA XAML
				CMP L			; Compare ‘examine index’ to hex data.
				LDA XAMH
				SBC H
				BCS TONEXTITEM	; Not less, so no more data to output.
				INC XAML
				BNE MOD8CHK		; Increment ‘examine index’.
				INC XAMH

MOD8CHK:		LDA XAML		; Check low-order ‘examine index’ byte
				AND #$07		;	For MOD 8=0
				BPL NXTPRNT		; Always taken.

PRBYTE:			PHA				; Save A for LSD.
				LSR
				LSR
				LSR				; MSD to LSD position.
				LSR
				JSR PRHEX		; Output hex digit.
				PLA				; Restore A.

PRHEX:			AND #$0F		; Mask LSD for hex print.
				ORA #'0'+$80	; Add "0".
				CMP #$BA		; Digit?
				BCC ECHO		; Yes, output it.
				ADC #$06		; Add offset for letter.

ECHO:			AND #$7F		; Mask out top bit for compat
				STA DSP			; Output character. Sets DA.
				ORA #$80		; Add high bit again for compat
				RTS				; Return.