* Ex_Sort.ASM

*12456789012345678901245678901234567890124567890123456789

#INCLUDE	'A:\VAR_DEF.ASM'

* Define program variables
	ORG	DATA
STEP	RMB	1	; +1=FORWARD; -1=BACKWARD
DELAY	RMB	1	; $28 < DELAY < $ff 

* Main program
	ORG	PROGRAM
START	LDX	#REGBAS
* Initialize SCI
	LDAA	#%00110000	; initialize BAUD=9600
	STAA	BAUD,X
	LDAA	#%00000000	; initialize 8-bit word
	STAA	SCCR1,X
	LDAA	#%00001100	; initialize TE and RE
	STAA	SCCR2,X

* Initialize controls
	LDAA	#0	; set stand still as default
	STAA	STEP
	LDAA	#$ff	; set slow (DELAY=$ff) as default
	STAA	DELAY	
* Start looping
LABEL0	NOP
* Check for keystroke reception
LABEL1	LDAA	SCSR,X		; check if RDRF is set
	ANDA	#%00100000	; mask for RDRF
	BEQ	LABEL9
* You are here after the keystroke was received
	LDAB	SCDR,X		; load keystroke
* Echo the keystroke
LABEL2	LDAA	SCSR,X	; check if TDRE is set
	ANDA	#%10000000	; mask for TDRE 
	BEQ	LABEL2
* You are here when the transmission reg. is empty
	STAB	SCDR,X	; transmit back keystroke
* Decipher and sort keystroke
	CMPB	#'>'	
	BEQ	FORWD
	CMPB	#'<'
	BEQ	BACKWD
	CMPB	#'+'
	BEQ	FASTER
	CMPB	#'-'
	BEQ	SLOWER
	CMPB	#'S'
	BEQ	STOP
	JMP	LABEL9
FORWD	LDAA 	STEP
	CMPA	#+1
	BGT	LABL10	
	INCA	
LABL10	STAA	STEP
	JMP	LABEL9
BACKWD	LDAA	STEP
	CMPA	#-1
	BLT	LABL11
	DECA
LABL11	STAA	STEP
	JMP	LABEL9
FASTER	LDAA	DELAY	; reduce delay
	CMPA	#$28	; but not below $28
	BLS	LABEL6
	DECA	
LABEL6	STAA	DELAY
	JMP	LABEL9
SLOWER	LDAA	DELAY	; increase delay
	CMPA	#$ff	; but not over $ff
	BHS	LABEL7
	INCA
LABEL7	STAA	DELAY	
	JMP	LABEL9
STOP	SWI

LABEL9	BRA	LABEL0	; back to the top
	
	ORG	RESET	; reset vector
	FDB	START	; set to start of program