...DFX is an RSX program to do absolute disk patches on
	to your current SY: disk. calling sequence is via a 
	
	MCR>DFX
	
	In response to "ENTER DISK BLOCK #" type block number in octal
	or "E" to exit to RSX. The block will be read in and can be
	displayed by the "L" command. display is on LUN 6
	
	Note that LUN 2 is used for disk reads and LUN 4 for disk writes,
	as a protective measure LUN 4 is assigned to pseudo device XX:
	and must be re-assigned by the user before to enable write-back
	
	Also note that LUN 6 is used for full block listings. it is initially
	set to TI: but can be re-assigned to a disk, and will be in the users
	UIC as "DFX.DAT"
	
	In response to "DFX>" prompt, type
	 
	L	to list referenced block
	W	to write the currently referenced block back onto disk
	N	to read the next block
	R	to reread the current block (overwriting current buffer)
	B	to read the previous block
	F	for full-word addresses (defaults to byte addresses)
	H	for half-word (byte) addresses in block
	T	to type out the block as ascii text
	S	to set/clear flag for spooling output file to LP0:
		if LUN 6 is a disk, the file will be spooled on exit or when
		the spooling flag is cleared by the operator
	K	to calculate checksum of first 255. words of block
	E	to exit to the monitor
	 
	there are 4 M(odify) type commands, where 
		M=the byte offset of the buffer word to be listed/modified
		Note that for M commands, M must be even, 0 <= M < 1000
 
	M/000000	change buffer word to the octal value 000000
	M,LLL		change buffer word to rad50 vaLue of "LLL"
	M;AA		change buffer word to ascii value of "AA"
	M:		display buffer word in octal, rad50 and ascii
 
	 
	there are 4 commands which alter the ablsolute block number
 
	D,N	to change default block number for read and write to N with-
		out changing the contents of the buffer in core. this should
		permit moving data from one block to another.
	A,N	to read and list block N (N absent implies next block)
	C,N	to read and list all blocks up to and including block N.
	 	(N absent implies to end of disk.)
	P,N	changes the high-order block number from the disk.
		no I/O will be done, but the block number will be copied
		from the high-order and low-order blocks to relative
		words 400 & 401 (byte offset 1000 & 1002) past the IO buffer
		where the single-word examining commands can see them.