rcsr = 177560
rbuf = 177562
xcsr = 177564
xbuf = 177566
 
	.psect .txt
	.title echo
start:	
	mov 	#40,r3
	tstb	@#rcsr
	bge	start
	mov	@#rbuf,r1
	cmpb	r1,#40
	ble	noxor
	xor	r3,r1
noxor:	mov	r1,@#xbuf
	br	start
.byte 123
.end start