sample

Table: dc.w S1,S2,S3,S4,
		 S1,S2,S3,S4,
		 S1,S2,S3,S4,
		 S1,S2,S3,S4

TB1: dc.b T1,T2,T3,T4,
		  T1,T2,T3,T4,
		  T1,T2,T3,T4,
		  T1,T2,T3,T4
		 
Input (in sequence): PORTH:  0,1,2,3,8,15
	
Output: PORTA = ????

	 
Begin:

	ldx #Table		(x <- index)
	ldab PTH 		(b <- PTH)
	andb #$0F; 		(b <- PTH & 0x0F)
	clra 			(PORTA = 0)
	rolb 			(PORTB <- PORTB * 2) 
	jsr[D,x]		(call Table[PTH])
	
bra Begin

S1: movb #T1, PORTB;
	jsr S5
	rts
	
S2: movb #T2, PORTB;
	jsr S5;
	rts

S3: movb #T3, PORTB;
	jsr S5;
	rts
	
S4: movb #T4, PORTB;
	jsr S5;
	rts	

S5: 
	lsrb (PORTB <- 2 * (PTH & 0x0f))
	negb
	sex B,D (D <- -PORTB)
	
	ldx #Tbl	(X <- Tbl)
	leax D,x	(X <- Tbl - PORTB)
	
	ldab 15,x   (PORTB <- Tbl - PORTB + 15 = Tbl[15-PORTB])
	stab PORTA  (PORTA <- PORTB)
	rts