.PAGE
;
;	CALCULATE THE TTY UNIT NUMBER
;	INPUTS	R5 = TTY UCB ADDRESS
;	OUTPUTS	R5 = TTY UNIT NUMBER
;
TTYCLC:	MOV	R4,-(SP)		;SAVE OTHER REGISTERS
	MOV	R3,-(SP)		;
	MOV	R2,-(SP)		;
	MOV	R1,-(SP)		;
	MOV	U.DCB(R5),R4		;GET BACK TO THE DCB
	MOV	D.UCBL(R4),R2		;GET LENGTH OF A UCB
	MOVB	D.UNIT(R4),R1		;GET STARTING UNIT NUMBER
	MOV	D.UCB(R4),R3		;GET ADDRESS TO 1ST UCB
	SUB	R3,R5			;CALCULATE TTY UCB OFFSET
	CLR	R4			;INIT FOR DIVIDE
	DIV	R2,R4			;DIVIDE OFFSET BY SIZE OF A UCB
	MOV	R1,R5			;GET 1ST UNIT NUMBER
	ADD	R4,R5			;CALC OUR TTY UNIT NUMBER
	MOV	(SP)+,R1		;GET OUR REGS BACK
	MOV	(SP)+,R2		;
	MOV	(SP)+,R3		;
	MOV	(SP)+,R4		;
	RETURN				;AND RETURN
	.END	START