hacking

	==Phrack Magazine==

	Volume Four, Issue Forty-Two, File 8 of 14

	USEFUL COMMANDS FOR THE TP3010 DEBUG PORT

	BY G. TENET


	ALL OF THE COMMANDS LISTED BELOW, INDICATE A LENGTH IN ALL THE READ
	COMMANDS. THE LENGTH OF THE READ COMMANDS MAY VARY DUE TO
	CONFIGURATION OPTIONS AND SOFTWARE VERSION.

	1) L7FE,L,A,R200

	THIS COMMAND STRING WILL LOAD '7FE' INTO THE MEMORY POINTER
	REGISTER THEN LOAD THE CONTENT OF '7FE' AND '7FF' INTO THE MEMORY
	POINTER REGISTER. THE 'A' THEN INCREMENTS THE CONTENTS OF THE MEMORY
	POINTER REGISTER. THE 'R200' COMMAND THEN READS 200 BYTES BEGINNING
	AT THE LOCATION SPECIFIED BY THE MEMORY POINTER REGISTER.
	THIS AREA IS USED FOR STORING THE LOADED CONFIGURATION. DUE TO THE
	VARIABLE NATURE OF THE CONFIGURATION RECORDS, THE READ COMMAND MAY HAVE
	TO BE MODIFIED DEPENDANT ON THE NUMBER OF LINES DEFINED, THE TYPE OF LINES
	DEFINED (X780,3270) AND THE TYPE OF SOFTWARE LOADED (4.2X OR 5.0X).


	2) LC4,R3,LCC,R3 (4.2X SOFTWARE)
	L124,R3,L131,R3 (5.0X SOFTWARE)

	THIS COMMAND STRING WILL DISPLAY THE BUFFER MANAGER CONTROL BLOCK AREA
	WHICH HAS BUFFER COUNTS WHICH MAY SUGGEST POSSIBLE PROBLEMS.


	3) L32C,R (4.2X SOFTWARE)
	L29C,R (5.0X SOFTWARE)

	THIS COMMAND STRING WILL DISPLAY THE NUMBER OF ACTIVE VC'S IN THE
	TP3 AT THAT MOMENT.

	IF THIS COMMAND IS USED VIA THE LOCAL CONSOLE, THE VC COUNT WILL NOT
	INCLUDE THE USER CONNECTION BECAUSE THERE WILL BE NO VC ON THE X.25 LINE
	FOR THE LOCAL CONSOLE.

	4) L70,R60

	THIS COMMAND STRING WILL DISPLAY THE LCB (LINE CONTROL BLOCK) POINTER
	FOR THE CONFIGURED LINES.

	THE ORDER THAT THE LCB POINTERS ARE ENTERED ARE: CONSOLE LCB, X.25 LCB,
	LINE 1, LINE 2, LINE 3...LINE27. ANY ZERO ENTRY IS AN UNCONFIGURED
	LINE EACH LINE ENTRY IS TWO BYTES LONG.


	5) L300,L,R20 (4.2X SOFTWARE)
	L270,L,R20 (5.0X SOFTWARE)

	THIS COMMAND STRING WILL DISPLAY THE LCN VECTOR TABLE. THE ENTRIES ARE
	FOR EACH ACTIVE LCN BEGINNING WITH LCN 0 THRU THE HIGHEST CONFIGURED
	LCN. A 0000 ENTRY FOR AN LCN WILL INDICATE THAT THE LCN IS NOT ACTIVE.
	A NON ZERO ENTRY WILL POINT TO THE DCB (DEVICE CONTROL BLOCK) OF THE
	ASSOCIATED LINE/DEVICE.

	6) L1F1,L,R20 (4.2X SOFTWARE ONLY)

	THIS COMMAND STRING WILL DISPLAY THE PROTOCOL ID TABLE FOR THE
	CONFIGURED/SUPPORTED PROTOCOLS. THE FORMAT OF THE OUTPUT
	IS:
	999999999999...
	-- ----
	! -- ! ----
	! ! ! !...............POINTER TO THE SERVER TABLE *****
	! ! !...................POINTER TO THE PROTOCOL SERVICE ROUTINE
	! !......................PROTOCOL ID NUMBER
	! 01 =ITI (RITI AND LITI)
	! 4B =X780
	! 47 =NAP 3270
	! 09 =DEBUG
	!........................NUMBER OF ENTRIES IN THIS TABLE


	7) L(ADDRESS OF THE SERVER TABLE),R20

	THE ADDRESS OF THE SERVER TABLE IS FOUND IN #6 (ABOVE)
	THIS COMMAND WILL DISPLAY THE SERVER TABLE IN THE FORMAT:

	99999999...
	-- ----
	! -- !................ THIS IS THE ADDRESS OF THE FIRST FREE DCB
	! ! IN THE FREE DCB LIST. IF 0000 THEN THERE ARE
	! ! NO FREE DCB'S FOR THIS SERVER AND PROTOCOL.
	! !.....................SERVER NUMBER
	!.......................NUMBER OF ENTRIES IN THIS TABLE


	THE POINTER IN THIS TABLE , IF PRESENT, WILL POINT TO THE NEXT AVAILABLE
	DCB. WITHIN THE DCB, THERE IS A POINTER AT DISPLACEMENT 18 AND 19 WHICH
	WILL POINT TO THE NEXT FREE DCB. THE LAST FREE DCB WILL HAVE A
	POINTER OF 0000.

	THE FOLLOWING COMMANDS ARE USED WITHIN THE TP3 DEBUG PORT TO
	PERFORM THE INDICATED ACTIONS. ONLY THE TP3325 WILL SUPPORT THE
	[# LPU NUMBER] OPTIONS. THE USE OF THE [# LPU NUMBER] OPTION IS ONLY
	REQUIRED IF YOU WISH TO ADDRESS A DIFFERENT LPU NUMBER; EXCEPT FOR THE
	'S' COMMAND WITH WHICH THE LPU MUST BE DEFINED.

	A SPACE CHARACTER MAY BE INCLUDED IN THE COMMAND AND THE COMMANDS
	MAY BE STACKED (EXAMPLE: L7FE ,L,A,R5,L#2,L 7FE,L,A,R5,L#3 7FE,L,A,R 5).

	THE TP3325 COMMANDS THAT DO NOT USE THE 'LPU' PARAMETER USE THE
	LAST ASSIGNED LPU NUMBER. (EXAMPLE: L#27FE,R2,L#17FE,R4)
	THE FIRST LOAD COMMAND ADDRESSES LPU 2 AND THE NEXT LOAD COMMAND ADDRESSES
	LPU 1. THE READ OF TWO BYTES IS READING FROM LPU 2 AND THE READ OF FOUR
	BYTES IS READING FROM LPU 1.

	A VALUE
	INCREMENTS THE MEMORY ADDRESS POINTER.
	(EXAMPLE: A5 OR AFFE2 OR A#2EF)

	B VALUE
	USED TO ENTER OR EXIT BINARY MODE.
	(EXAMPLE: B01 OR B00)

	C [# LPU NUMBER] VALUE
	USED TO WARM OR COLD START A TP3325 LPU
	(EXAMPLE: C00 OR C#300)
	OR
	USED TO WARM OR COLD START OTHER TP3.
	(EXAMPLE: C01 OR C#201)

	D VALUE
	USED TO DECREMENT THE MEMORY POINTER.
	(EXAMPLE: D18 OR DFFE5 OR D#4IFF)

	E STRING
	USED TO CHECK FOR A EQUAL COMPARE OF MEMORY DATA.
	(EXAMPLE: E00 OR E0F0304 OR E#20000)

	F STRING
	USED TO FIND THE FIRST OCCURRENCE OF A STRING.
	(EXAMPLE: F0F0304 OR F08080202 OR F#308080404)

	G [# LPU NUMBER] VALUE
	USED TO FIND THE ADDRESS OF A CONFIGURATION FILE IN
	MEMORY. THE LPU DEFINITION IN THE COMMAND DOES
	NOT CHANGE THE LPU ASSIGNMENT IN THE DEBUG PORT.
	(EXAMPLE: GFE OR G01 OR G#301)

	I [# LPU NUMBER]
	USED TO OBTAIN A LIST OF THE CONFIGURED LINE TYPES.
	(EXAMPLE: I OR I#3)

	K [# LPU NUMBER] [14 DIGIT ADDRESS]
	USED TO OBTAIN THE LCB, ADDRESS TABLE POINTERS AND
	LINE NUMBER ASSOCIATED WITH THE ADDRESS.
	(EXAMPLE: K31102120012301 OR K#2 311021250212)

	N STRING
	USED TO CHECK FOR AN NON EQUAL COMPARISON.
	(EXAMPLE: N0F0304 OR N08080202 OR N#1 0F)

	P [# LPU NUMBER] PORT NUMBER
	USED TO READ THE CONTENTS OF A SPECIFIC PORT REGISTER.
	(EXAMPLE: P45 OR P21 OR P#4 21)

	R VALUE
	USED TO READ MEMORY DATA. THE QUANTITY IS INDICATED
	BY THE 'VALUE'.
	(EXAMPLE: R18 OR R200)

	S [# LPU NUMBER] LINE NUMBER
	USED TO OBTAIN DATA SET SIGNALS FOR THE DEFINED LINE
	NUMBER.
	(EXAMPLE: S1 OR S#23 OR S)

	T (TP3325 ONLY)

	W STRING
	USED TO WRITE DATA INTO MEMORY.
	(EXAMPLE: W0E0304 OR W08080707)

	X [# LPU NUMBER]
	USED TO DISPLAY THE DIFFERENCE BETWEEN THE STORED
	CHECKSUM AND A CALCULATED CHECK SUM OF THE
	OPERATING SOFTWARE. THE LPU DEFINITION DOES
	NOT CHANGE THE LPU ASSIGNMENT IN THE DEBUG PORT.
	(EXAMPLE: X OR X#2)

	Y (TP3325 ONLY)
	RETURNS NCC LOAD ADDRESS FROM EPROM

	Z (TP3325 ONLY)
	CRASHES APB AND XPB. MAY HANG APB IF THE X.25
	INTERFACE DOES NOT RESET.

	$ PORT A -- ENABLE AUTOCONNECT
	M -- DISABLE AUTOCONNECT
	B -- BUSY
	R -- RESET
	C -- CLEAR

	HARDWARE COMMANDS FOR THE TP3000

	'P' COMMAND DISPLAYS THE STATUS OF A SPECIFIED PERIPHERAL INTERFACE
	DEVICE FOR THE CPU. FOLLOWING IS A LIST OF SOME OF THE MORE USEFUL ADDRESSES
	WHICH CAN BE BENEFICIAL IF TRYING TO RESEARCH A PROBLEM.
	THIS COMMAND IS A READ TO THE SPECIFIED DEVICE. DEPENDANT ON THE DEVICE
	BEING READ (THE ADDRESS), THE TP MAY CRASH.

	COMMAND INTERPRETATION
	======= ==============

	TP3010
	------
	P45 READ CONSOLE READ REGISTER
	(BIT 2 THRU 6 SHOW THE POSITION OF
	THE FRONT PANEL ROTARY SWITCH)
	BIT 0 = NOT TIMEOUT STATUS (SEE P47)
	BIT 1 = NOT PBRST STATE (SEE P47)
	BIT 2 = NOT RESTART
	BIT 3 = NOT MEMORY SAVE
	BIT 4 = NOT TAPE LOAD
	BIT 5 = NOT PROGRAM SAVE
	BIT 6 = NOT DIAGNOSTICS
	BIT 7 = NOT SYSTEM GOOD
	IF BIT 6 THRU BIT 2 ARE ALL SET (EQUAL TO 1)
	THEN THE FRONT PANEL SWITCH IS IN
	THE X.25 LOAD POSITION.
	P47 THIS COMMAND WILL CAUSE THE FRONT PANEL
	ALARM TO SOUND.

	P4D,P4D,P4D,P4D,P4D,P4D,P4D THE LAST RESPONSE WILL PROVIDE THE
	DOWN LINE LOAD EPROM REV. LEVEL
	FOR THE TP3010.
	EXAMPLE 43 = 'C' LEVEL
	TP3005
	------
	P23 BIT 1 = 0 CONFIG MODE
	1 RUN MODE

	4.2X 5.XX COMMENTS
	====== ====== ===========================================

	70 70 LCB VECTOR TABLE

	2 BYTES FOR EACH LINE IN THE TP. IF LINE IS
	NOT DEFINED , THEN ENTRY IS 0000. IF LINE
	IS DEFINED, THEN ADDRESS POINTS TO THE
	LCB (LINE CONTROL BLOCK)

	C0 120 BM CONTROL BLOCK
	C4 124 # CONTROL BUFFERS INITIALIZED
	C5 125 # CONTROL BUFFERS FREE
	C6 126 LOWEST # CONTROL BUFFERS (00 IS NONE LEFT)
	12B POINTER TO THE CONTROL BUFFERS
	CC 131 # BLOCK BUFFERS INITIALIZED
	CD 132 # BLOCK BUFFERS FREE
	CE 133 LOWEST # BLOCK BUFFERS REACHED (00 IS NONE
	LEFT)
	138 POINTER TO BLOCK BUFFERS
	1F1 POINTER TO PROTOCOL ID TABLE

	270 1F0 X.25 LCB
	27E 27E # FRAMES DISCARDED
	27F 27F # CRC ERRORS
	280 280 # REJECTS SENT
	281 281 # REJECTS RECEIVED
	282 282 # T1 TIME OUTS
	283 283 # COMMAND REJECTS SENT
	284 284 # COMMAND REJECTS RECEIVED
	285 285 # DISCONNECTS SENT
	286 286 # DISCONNECTS RECEIVED
	287 287 # SET MODE SENT
	288 288 # SET MODE RECEIVED
	289 289 # FRAME OVERFLOW RECEIVED
	28A 28A # I FRAMES SENT
	28B 28B # I FRAMES RECEIVED
	2B0 230 DMA LCB

	300 270 LCN VECTOR TABLE

	29B MAX. # LCN'S
	32C 29C # OF ACTIVE LCN'S

	7FE 7FE POINTER TO THE END OF THE OPERATING
	SYSTEM. THE NEXT BYTE IS THE BEGINNING
	CONFIGURATION TABLES.

	159 E9 TIME OF DAY CLOCK
	159 E9 1/10 SECONDS
	15A EA SECONDS
	15B EB MIN.
	15C EC HOURS
	15D ED DAYS
	15E EE DAYS

	DCB + 3 XX PACKET REC. STATUS BYTE#1
	00 = READY
	01 = DTE WAITING
	02 = DCE WAITING
	04 = DATA TRANSFER
	08 = DTE CLEAR REQUEST SENT
	10 = DCE CLEAR INDICATION
	20 = DTE RESTART REQUEST
	40 = DTE RESET REQUEST
	80 = DCE RESET INDICATION
	DCB +18 XX POINTER TO NEXT FREE DCB
	VALID ONLY IF THIS IS A FREE DCB

	ITI SPECIFIC LCB INFORMATION

	LCB+27 PHYSICAL STATUS
	X'00' LINE DOWN/INACTIVE
	X'01' LINE HAS BEEN INACTIVATED
	X'02' LINE IS 'BUSY OUT'
	X'04' LINE IS BEING ACTIVATED
	X'08' LINE IS ACTIVE
	X'10' LINE IS BEING INACTIVATED

	LCB+28 TDT2 COMMAND BYTE
	BIT 0 = 1 BUSY LINE
	BIT 1 = 1 CLEAR LINE
	BIT 2 = 1 RESET LINE
	BIT 3 - 7 NOT USED

	LCB+5C # BUFFERS ALLOCATED TO THIS LINE
	LCB+5D DRIVER ERROR COUNTER
	LCB+5E NO BUFFER ERROR COUNTER
	LCB+5F FLOW CONTROL ERROR COUNTER
	LCB+60 PARITY ERROR COUNTER
	LCB+61 OVER-RUN ERROR COUNTER
	LCB+62 FRAMING ERROR COUNTER
	LCB+74 BREAK TIMER
	LCB+75 RING-OUT TIMER
	LCB+76 RING-OUT COUNTER

	DSP 3270 LCB SPECIFIC INFORMATION

	LCB+4F CURRENT NO. SYNC PAIRS INSERTIONS
	LCB+50 CURRENT NO. OF ERROR RETRIES
	LCB+51 CURRENT NO. OF NAK RETRIES
	LCB+52 CURRENT NO. OF ENQ RETRIES
	LCB+53 RECEIVE ACK COUNTER
	LCB+54 TRANSMIT ACK COUNTER
	LCB+55 CTS DROP-ERROR COUNTER
	LCB+56 DCD DROP-ERROR COUNTER
	LCB+5A CURRENT NO. WACK'S


	X780 LCB SPECIFIC INFORMATION

	LCB+4F CURRENT NO. OF SYNC PAIR INSERTIONS
	LCB+50 CURRENT NO. OF ERROR RETRIES
	LCB+51 CURRENT NO. OF NACK RETRIES
	LCB+52 CURRENT NO. OF ENQ RETRIES
	LCB+53 RECEIVE ACK COUNTER
	LCB+54 TRANSMIT ACK COUNTER
	LCB+55 CTS DROP-ERROR COUNTER
	LCB+56 DCD DROP-ERROR COUNTER


	COMMON DCB INFORMATION

	DCB+6 BITS 5-7 PACKET SEND SEQ. NO. P(S)
	DCB+7 BITS 5-7 PACKET REC. SEQ. NO. P(R)
	DCB+8 LCN #
	DCB+9 BITS 5-7 PACKET SEQ. NO. LAST CONFIRMED
	DCB+A BITS 5-7 PACKET SEQ. NO. LAST SENT TO NET
	DCB+B # PACKETS SENT
	DCB+D # PACKETS REC.
	DCB+F # RESETS SENT OR RECEIVED
	DCB+14 # BUFFERS IN HOLD QUEUE
	DCB+15 TIME VC WAS ESTABLISHED (SSMMHHDD)
	DCB+31 DESTINATION NETWORK ADDRESS



	THE FOLLOWING IS A DESCRIPTION OF THE TP3006 X.25 INTERFACE FROM THE
	SIO TO THE REAR PANEL CONNECTORS.

	SIO CHIP REAR PANEL CONNECTOR
	+--------------+
	\| \|
	\| DTRB \|------------------->- DTR 20
	\| TXDB \|------------------->- TXD 2
	\| RTSA \|------------------->- LDL 13
	\| RTSB \|------------------->- RTS 4
	\| DTRA \|------------------->- LAL 19
	\| DCDA \|---<-----------+--->- CTR 18
	\| \| +---<- RLSD 8
	\| RXCA \|--+
	\| RXCB \|--+-------- ** ----<- RXC 17
	\| \| +->- TXCE 24
	\| \| ** --+->- RXCE 11
	\| TXCA \|----+
	\| TXCB \|----+------ ** ----<- TXC 15
	\| DCDB \|----------- ** ----<- DSR 6
	\| CTSB \|-------------------<- CTS 5
	\| RXDA \|----+
	\| RXDB \|----+--------------<- RXD 3
	\| CTSA \|-------------------<- RI 22
	\| \|
	+--------------+

	< INBOUND SIGNAL
	> OUT BOUND SIGNAL

	IF DSR AND TXC, THEN USE EXTERNAL CLOCKING. IF DSR AND NO TXC,
	THEN USE INTERNAL CLOCKING DERIVED FROM THE CONFIGURED LINE SPEED
	PRODUCED FROM A CTC CHIP). IF THE CLOCKING IS PRODUCED INTERNALLY,
	THEN THE INTERNAL CLOCK IS ALSO PROVIDED ON PINS 11 AND 24
	AT THE REAR PANEL.

	FOR THE TP3325, THE NETLINES ALWAYS USE THE EXTERNAL CLOCK SOURCE.
	THE HARDWARE WAS CHANGED DURING REFINEMENT OF THE MOD ONE XPB.

	IF THE ATTACHED DEVICE IS PROVIDING CLOCKING AND THE TP3025 IS PROVIDING
	CLOCKING, THE TP WILL DETECT THE CLOCKING AND WILL STOP CLOCKING. IN THE
	CASE OF THE TP3025 HAVING BEEN RESET AND LOADED, IF A TP3005/3006 IS THEN
	CONNECTED TO THE INTERFACE, THERE IS A RACE CONDITION WHERE THE DEVICE THAT
	PROVIDES THE CLOCKING IS ARBITRARY. THE HARDWARE LOGIC REQUIRES A RESET
	TO OCCUR FOR THE TP3025 TO CHANGE PRIOR SELECTION OF 1) INTERNAL/EXTERNAL
	CLOCKING AND 2) V35/RS232 INTERFACE AFTER A LOAD.

	THE DEBUG PORT "S" COMMAND WILL RETURN ONE HEX BYTE THAT REPRESENTS
	THE DATA SET SIGNALS STATUS AT THE SIO CHIP FOR THE DEFINED LINE
	(E.G. "S2" WILL RETURN THE DATA SET SIGNALS ON LINE 2). THE UPPER HALF
	OF THE BYTE IS USED TO REPRESENT THE DATA SET SIGNAL STATUS.

	BIT 7 6 5 4 3 2 1 0
	\| \| \| \| ==========
	\| \| \| \| NOT USED
	\| \| \| \|
	DSR AT THE REAR ---+ \| \| +--- RTS AT THE REAR PANEL.
	DTR AT THE REAR -----+ +------ CTS AT THE REAR PANEL.

	THE FOLLOWING IS A DESCRIPTION OF THE DEVICE INTERFACE FOR THE
	SIO TO THE REAR PANEL.

	SIO CHIP REAR PANEL INTERFACE
	+--------------+
	\| \|
	\| RXD \| ------------------------< 2 TD
	\| TXD \| ------------------------> 3 RD
	\| DCD \| -<-----------+----------< 4 RTS
	\| \| +----------> 5 CTS
	\| DTR \| ------------------------> 6 DSR
	\| RTS \| ------------------------> 8 DCD
	\| RXC \| -<--------- ** ---------< 11
	\| \| PIO DSR -- ** ---------< 20 DTR
	\| \| -- ** ---------> 15 TC
	\| \| -- ** --------> 17 RC
	\| TXC \| -<--------- ** ---------< 24 TC
	\| CTS \| -<----------------------< 18
	\| \|
	\| \| PIO -----------------< 25
	\| \| PIO -----------------> 22
	\| \|
	+--------------+

	WITH DTR TRUE ( PIN 20), RXC (PIN 11) IS CHECKED FOR AN INBOUND CLOCK
	SIGNAL. IF THERE IS A CLOCK SIGNAL, THEN THE SIO IS CLOCKED EXTERNALLY
	FROM PIN 11 AND 24. IF THERE IS NO CLOCK ON PIN 11 THEN AN INTERNAL CLOCK
	SOURCE IS GATED TO THE SIO AND TO PIN 15 AND 17 ON THE REAR PANEL INTERFACE.

	THE OUTPUT OF THE DEBUG PORT 'S' COMMAND DISPLAYS ONE HEX BYTE THAT
	IS A COMPOSITE OF THE DATA SET SIGNALS FROM THE PIO AND SIO CHIPS. THE
	OUTPUT BIT DEFINITIONS ARE THE SAME AS THE X.25 LINE BUT A NOTE NEEDS
	TO MADE THAT THE X.25 IS A DTE INTERFACE AND THE DEVICE LINES ARE A
	DCE INTERFACE. THE UTILIZATION OF THE INBOUND RTS/CTS MAY NOT BE
	REQUIRED FOR THE TP TO MAINTAIN THE INTERFACE.

	PINS 22 AND 25 ARE PAD DEPENDANT SO THEY MAY BE USED FOR
	DIFFERENT FUNCTIONS THAN THOSE EXPECTED.

	ALL NUMERIC VALUES ARE IN HEX.
	COMMAND STRINGS CAN BE USED WHILE IN THE DEBUG PORT.

	==============================================================<
	\| XCB DIRECTORY TABLE (two bytes per entry) >
	\| DEBUG \|LOGGER\| X.25 #0 \| X.25 #1 \| X.25 #2 \| X.25 #3\|.......
	L70,R24 \| DCB \| DCB \| XCB \| XCB \| XCB \| XCB \| >
	\|===============================================================>
	\| \| \| \| \| \|
	XCB#0 XCB#1 \| XCB#2 XCB#3 \| XCB#4 XCB#5
	\| \| \| \| \| \|
	+->>---------------->>-+ \| \| +>>+ \| \|
	\| \| \| \| \| \|
	\| +<<----------------<<-+ L76,R2 \| \| L7A,R2
	\| \| \| \|
	\| \| L74,L,R80 \| +<<---+ L78,L,R80
	\| \| \| \|
	\| +------------->>--------------> \| +--------->>------------->
	\| \| XCB >> > \| \| XCB >> >
	\| +------------->>--------------> \| +--------->>------------->
	\| \| XCB+2D \| \| XCB+2D
	\| \| +>>+ \|
	\| +-<<---------------+ \| +-<<-------------+
	\| \| \| \|
	\| \| L(XCB+2D),L,R((MAX.LCN3)+3) \| \| L(XCB+2D),L,R((MAX.LCN3)+3)
	\| \| \| \|
	\| +------------------>>--------> \| +------------------>>-------->
	\| \| LCN VECTOR TABLE >> ABCCDD > \| \| LCN VECTOR TABLE >> ABCCDD >
	B \|3 BYTES PER ENTRY >> ====== > B \|3 BYTES PER ENTRY >> ====== >
	\| +------------------>>--------> \| +------------------>>-------->
	\| \| \| \|
	+--CC->> TRUNK LCNS -----> \| +--CC->> CONCENTRATOR LCNS \|
	\| \|LCN0 \|LCN1 \|... \| \| \|LCN0 \|LCN1 \|... \|
	\| +--->>--+ \|
	\| \|
	\| THREE BYTE LCN ENTRY ==> AB CC DD \|
	\| = == == \|
	\| \| \| \| \|
	\| XCB NUMBER ----+ \| \| \|
	\| LCN NUMBER ------+ +---- LCN TIMER \|
	\| \|
	\| \|
	+-<<-----------------------------------------------------<<-------+

	** CC IS THE LCN NUMBER IN XCB B. B IN XCB #0 WILL POINT TO
	== = =
	XCB #4 IN THIS EXAMPLE. CC IN XCB #0 WILL GIVE THE LCN NUMBER USED IN
	==
	THE LCN VECTOR TABLES FOR XCB #4.


	1) XCB OFFSETS DEFINITION

	XCB + 09 CONTROL DATA SET SIGNAL STATUS
	BIT 4 = 1 RTS HIGH
	5 = 1 CTS HIGH
	6 = 1 DTR HIGH
	7 = 1 DSR HIGH
	THE S COMMAND RETRIEVES THIS LOC.
	XCB + 0B POINTER TO LINE CONFIGURATION RECORD.

	XCB + 0E NUMBER OF FRAMES DISCARDED.
	XCB + 0F NUMBER OF CRC ERRORS

	XCB + 10 NUMBER OF REJECTS SENT
	XCB + 11 NUMBER OF REJECTS RECEIVED

	XCB + 12 NUMBER OF T1 TIMEOUT

	XCB + 13 NUMBER OF COMMAND REJECTS SENT
	XCB + 14 NUMBER OF COMMAND REJECTS RECEIVED

	XCB + 15 NUMBER OF DISCONNECTS SENT
	XCB + 16 NUMBER OF DISCONNECTS RECEIVED

	XCB + 17 NUMBER OF SET MODE SENT
	XCB + 18 NUMBER OF SET MODE RECEIVED

	XCB + 19 NUMBER OF FRAME OVERFLOW

	XCB + 1A NUMBER OF I FRAMES SENT
	XCB + 1C NUMBER OF I FRAMES RECEIVED

	XCB + 24 FLAG BYTE
	BIT 0 = 1 DCE-TO-DTE FLOW INIT
	1 = 1 DTE-TO-DCE FLOW INIT
	2 = 1 LINK RESET (DISC. OR SETMODE SENT
	3 = 1 DCE BUSY ( RNR SENT)
	4 = 1 IN TIMER RECOVERY
	5 = 1 SENT INTERNAL RESET. LAP RE-INIT.
	6 = 1 SET POLL BIT IN NEXT FRAME.

	XCB + 27 LINE STATUS
	BIT 0 = 1 NOT ACTIVE
	1 = 1 DEACTIVATED
	2 = 1 BUSY-OUT
	3 = 1 ACTIVATING
	4 = 1 ACTIVE
	5 = 1 DEACTIVATING

	XCB + 2B MAX. LCN PERMITTED
	XCB + 2C CURRENT NUMBER OF LCN IN USE
	XCB + 2D POINTER TO THE LCN VECTOR TABLE

	XCB + 47 'DISABLE/ ENABLE/ CLEAR COMMAND.
	NOT OPERATIONAL AT VERSION 1.01.
	01 - BUSY
	02 - CLEAR BUSY
	04 - RESET LINE

	2) LCN VECTOR TABLE.
	( XCB + 2D ,L,A (LCN ADDRESS),R3)
	LCN ADDRESS = (LCN * 3)

	LCN + 0 BITS
	0-3 - XCB DIRECTORY NUMBER.
	4 - INIT CLEAR TIMER ON
	5 - CLEAR INDICATION SENT
	6 - CALL REQUEST SENT
	7 - LCN ACTIVE
	LCN + 1 LCN NUMBER
	(SEE LCN + 0 , BITS 0-3 TO GET XCB NUMBER)
	LCN + 2 TIMER FOR LCN.