#include 	"c:\miniide\hcs12.inc"
CR		equ	$0D
LF		equ	$0A
		org	$1000
buf		ds.b	60
cx		ds.b	1
		org	$2000
 		lds	#$1800		; set up stack pointer
		movw	#SCI0_isr,UserSCI0	; set up SCI0 interrupt vector
		jsr	init_SCI0
		jsr	newline		;move cursor to the next line
		ldx	#msg1
		jsr	puts2SCI0
		jsr	newline
		ldx	#prompt		; prompt the user to enter a string
		jsr	puts2SCI0		;	"
		ldx	#buf			; read a string from the keyboard
		jsr	getsSCI0		;	"
		jsr	newline		; move cursor to next line
		ldx	#buf			; echo the entered string to the monitor
		jsr	puts2SCI0		;	"
		jsr	newline		; move cursor to the next line
		cli
		ldx	#msg2			; output msg2 using interrupt-driven method
		jsr	puts_SCI0		;	"
		jsr	newline
		swi
msg1		fcc	"This is polling version."
		db	0
prompt	fcc	"Enter a message:"
		db	0
msg2		fcc	"This is interrupt message!"
		db	0

; **************************************************************************
; The following subroutine uses interrupt-driven approach to output a string
; pointed to by index register X to SCI0.
; **************************************************************************
puts_SCI0	bset	SCI0CR2,$80		; enable transmission and TDRE interrupt
		cli				; enable global interrupt
loop		ldaa	0,x			; get a character to be output
		bne	loop			; reach the end of string? 
		bclr	SCI0CR2,$80		; disable TDRE interrupt
		sei
		rts
		
SCI0_isr	ldab	SCI0SR1		; clear the RDRF flag
		staa	SCI0DRL		; output the character in A
		inx
		stx	3,sp
		rti
; **************************************************************************
; The following subroutine outputs a CR/LF pair to move cursor to the next
; line.
; **************************************************************************
init_SCI0	movb	#$00,SCI0BDH
		movb	#156,SCI0BDL	; set baud rate to 9600
		movb	#$4C,SCI0CR1
		movb	#$0C,SCI0CR2
		rts
; **************************************************************************
; The following subroutine move the cursor to the start of the next row.
; **************************************************************************
newline	ldaa	#CR
		jsr	putc2SCI0
		ldaa	#LF
		jsr	putc2SCI0
		rts
; **************************************************************************
; The following subroutine outputs a character to SCI0 using polling method.
; **************************************************************************
putc2SCI0	brclr	SCI0SR1,TDRE,*
		staa	SCI0DRL
		rts		
; **************************************************************************
; The following subroutine outputs a NULL-terminated pointed to by X using
; the polling method.
; **************************************************************************
puts2SCI0	ldaa	1,x+
		beq	done_puts
		jsr	putc2SCI0
		bra	puts2SCI0
done_puts	rts
; *****************************************************************************
; The following function uses the polling method to read a character from SCI0.
; *****************************************************************************
getcSCI0	brclr	SCI0SR1,RDRF,*	; wait for the arrival of a character
		ldaa	SCI0DRL		; read the character
		rts
; ****************************************************************************
; The following function uses the polling method to read a string from SCI0.
; and store the string in a buffer pointed by index register X.
; The string is terminated by the carriage return.
; ****************************************************************************
getsSCI0	jsr	getcSCI0
		cmpa	#CR			; is it a carriage return
		beq	donegets
		staa	1,x+			; save the character and increment the pointer
		bra	getsSCI0
donegets	clr	0,x			; terminate the string by a NULL character
		rts
		end