INCHAR	EQU	$ffcd 
OUTSTRG	EQU	$ffc7 
OUT1BYT	EQU	$ffbb
OUTA	EQU	$ffb8

ESC	EQU	27
CRLF	EQU	13
EOT	EQU	04

BKSPC	EQU	08
TAB	EQU	09

DATA1	EQU	$c500
OPADDR	EQU	$C504
DATA2	EQU	$C505
DATAEND	EQU	$c509	 
RESULT	EQU	$c509
REND	EQU	$c50d

PIOC	EQU	$1002	
PORTB	EQU	$1004
PORTC	EQU 	$1005
DDRC	EQU	$1007

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

	ORG	$c600

PROMPT	FCB	#CRLF
	FCC	"PLEASE USE THE FORM AAAAAAAA _ AAAAAAAA"
	FCB	#CRLF
	FCC	"WHERE _ CAN BE ANY VALID OPERATOR ( + - * / )"
	FCB	#CRLF
	FCC	"USE enter TO SUBMIT AND esc TO QUIT."
	FCB	#CRLF
	FCB	#CRLF
	FCC	"       -> "
	FCB	#EOT

QPROMPT	FCC	"PROGRAM ABORTED."
	FCB	#EOT

DONE	FCC	"          = "
	FCB	#EOT

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

	ORG	$C000

START	LDS	#$CFFF		; init the stack pointer

;-----------------------------------------------------------

	LDX	#DATA1		; zero the data space
	LDAA	#0
ZEROING	STA 	0,X
	INX
	CPX	#REND
	BLO	ZEROING

;-----------------------------------------------------------

	LDX	#PROMPT		; prompt the user for input
	JSR	OUTSTRG

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

        LDAA	#0		; init the registers
	LDAB	#0
	LDX	#DATA1
	LDY	#0

;-----------------------------------------------------------
	
GETCHAR	JSR	INCHAR		; try to get char
	CMPA	#0		; did we get a char
	BEQ	GETCHAR		; if not, try again

	CMPA	#TAB		; look for illegal keys
	BEQ	QUIT

	CMPA	#BKSPC		; look for illegal keys
	BEQ	QUIT

	CMPA	#ESC		; quit if they hit escape
	BEQ	QUIT

	CMPA	#CRLF		; finish if they hit enter
	BEQ	EEVAL
	CPX	#DATAEND	; check if we're done
	BEQ	JUNK

	CPX	#OPADDR		; check if we're getting the opcode
	BEQ	OPEVAL

	CPX	#DATA2		; check for white space after the opcode
	BEQ	WEVAL

	BRA	GETHEX		; else we expect a hex digit

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

QUIT	LDX	#QPROMPT	; display the quiting prompt
	JSR	OUTSTRG
	JMP	START

;-----------------------------------------------------------

OPEVAL	CMPA	#'+'		; check for valid opcodes
	BEQ	ADDOP
	CMPA	#'-'
	BEQ	SUBOP
	CMPA	#'*'
	BEQ	MULTOP
	CMPA	#'/'
	BEQ	DIVOP

	CMPA	#' '		; allow leading spaces
	BEQ	GETCHAR		

	BRA 	JUNK		; else it is junk

ADDOP	LDAA	#$08		; set the opcode
	BRA	STORE
SUBOP	LDAA	#$09
	BRA	STORE
MULTOP	LDAA	#$0a
	BRA	STORE
DIVOP	LDAA	#$0b
	BRA	STORE

;-----------------------------------------------------------

WEVAL	CMPA	#' '		; allow leading spaces
	BEQ	GETCHAR	
	BRA	GETHEX		; else we expect a hex digit

;-----------------------------------------------------------

EEVAL	CPX	#DATAEND	; check if we're done
	BEQ	OPERATE
	JMP	QUIT		; else quit

;-----------------------------------------------------------

JUNK 	LDAA	#BKSPC
	JSR	OUTA		; output a backspace
 	LDAA	#' '
	JSR	OUTA		; output a space to erase what's there
 	LDAA	#BKSPC
	JSR	OUTA		; output a backspace
	JMP	GETCHAR	

;-----------------------------------------------------------

GETHEX	CMPA	#'0'		; get the hex value of the char
	BLO	JUNK
	CMPA	#'9'
	BLS	NUMBER

	CMPA	#'A'
	BLO	JUNK
	CMPA	#'F'
	BLS	UCASE

	CMPA	#'a'
	BLO	JUNK
	CMPA	#'f'
	BLS	LCASE

	BRA	JUNK		; else it is junk

NUMBER	SUBA	#$30		; convert from ascii to hex
	BRA	MOD
UCASE	SUBA	#$37
	BRA	MOD
LCASE	SUBA	#$57

MOD	CPY	#0
	BEQ	HIGHEND
LOWEND	ABA			; else we have the low-end so add high-end from B
	LDY	#0		; reset the flag
	BRA	STORE
HIGHEND LSLA			; move the value into the high end
	LSLA
	LSLA
	LSLA
	TAB			; store the result in B for use next cycle
	INY			; set the flag
	JMP	GETCHAR		

;-----------------------------------------------------------

STORE	STAA	0,X		; store the data
	INX
	JMP	GETCHAR		; get next chunk of data

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

OPERATE	JSR	ALTERA	

	LDX	#DONE		; display the result message
	JSR	OUTSTRG

	LDX	#RESULT		; display the result
OUTR	JSR	OUT1BYT
	CPX	#REND
	BLO	OUTR
	JMP	START		; back to be begining

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

DEBUG	;PSHX
	;LDX	#REND
	;STAA	0,X
	;JSR	OUT1BYT
	;PULX
	RTS			; display the data being moved

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
	
WAIT	LDAA	PORTC		; read port C to clear STAF bit
WLOOP	LDAA	PIOC		; check to see if PORTC data has changed
	ANDA	#$80
	BEQ	WLOOP
	RTS			; wait for response handshaking routine

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
	
ALTERA	LDAA	#$00
	STAA	DDRC		; set the direction of PORTC

	LDAA	#%00010011	
	STAA	PIOC		; configure PORTC for Handshaking

	LDAA	PORTC		; read PORTC to clear STAF bit

				;-------------------------------
OPCODE	LDAA	OPADDR		; send op code       
	STAA	PORTB
	JSR	DEBUG
	JSR	WAIT
				;-------------------------------
	LDX	#DATA1		; send first operand
OP1	LDAA	0,X
	STAA	PORTB
	JSR	DEBUG
	JSR	WAIT
	INX
	CPX	#OPADDR
	BNE	OP1
				;-------------------------------
	LDX	#DATA2		; send second operand
OP2	LDAA	0,X
	STAA	PORTB
	JSR	DEBUG
	JSR	WAIT
	INX
	CPX	#DATAEND
	BNE	OP2
				;-------------------------------
	LDX	#RESULT		; receive result
RES	JSR	WLOOP
	LDAA	PORTC     	;STRB is fired here
	STAA	0,X
	JSR	DEBUG
	INX
	CPX	#REND
	BNE	RES

 	RTS

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;