.TITLE	BITSWP
;SWAP BITS IN BYTE FOR 7TRK XFER TO DG SYSTEMS
;	CALL BITSWP(ADDR,NBYTES)
;TO SWAP BITS IN PLACE IN ARRAY.
; SWAPS LOW AND HIGH 4 BITS IN EACH BYTE.
	.GLOBL	BITSWP
BITSWP:
	MOV	2(R5),R0	;ADDRESS
	MOV	@4(R5),R1	;GET BYTE COUNT
	BGT	1$
2$:	RTS	PC		;RETURN ON NEG OR 0
1$:	MOVB	(R0),R2		;GET A BYTE
	MOV	R2,R3		;COPY
	ASH	#4,R2		;SHIFT LOW BITS UP
	ASH	#-4,R3		;AND HIGH BITS DOWN
	BIC	#^C360,R2	;LEAVE ONLY HIGH BITS ON
	BIC	#^C17,R3	;AND LOW BITS IN APPROPRIATE REGS
	BIS	R3,R2		;OR THEM BACK
	MOVB	R2,(R0)+	;STORE IN ARRAY
	DEC	R1		;COUNT DOWN BYTES TO DO
	BGT	1$		;TILL DONE
	RTS	PC		;THEN RETURN
	.END