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swskit-v21/documentation/breakout-box.mem
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|d|i|g|i|t|a|l| INTEROFFICE MEMORANDUM
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TO: DECnet Users DATE: 4-Mar-80
FROM: NCSS
EXT: HOTLINE (5911)
LOC/MAIL STOP: MR1-2/H22
SUBJ: Use of Breakout Box
The breakout box is a simple, cheap diagnostic tool which can be
used to monitor modem signals. This memo gives you some clues
regarding what to look for when using the breakout box on a DECnet
line.
If you are lucky and have a Datascope at your disposal, the top
row of lights on the Datascope may be used in lieu of a breakout
box.
In either case, a quick check of the line using a breakout box may
be enlightening if you are having troubles getting two DECnet
systems communicating, especially if you suspect that the modems
or the lines themselves may be at fault.
1.0 INSTALLING THE BREAKOUT BOX
The breakout box is hooked into the line between the line driver
(DUP or DMC) and the modem. First use the NCP command subset of
OPR to set the state of the line to OFF. Then find a place in the
line anywhere between the line driver and the modem where a
connection is made with a 25-pin EIA connector. Break this
connection and then reconnect the line with the breakout box in
the middle, whichever way the plugs will fit. Be sure all the
mini-switches on the box are set to normal, not open. Then turn
the line on again with OPR.
If your synchronous lines go through a Spectron or similar patch
panel, you can hook the breakout box into the patch panel. Insert
a patch between the monitoring plug for the modem on the patch
panel and the female plug on the breakout box. In other words,
the breakout box is acting as the monitor rather than the regular
monitoring plug on the side of the patch panel. This saves you
the trouble of having to turn the line on and off from OPR. To
make this patch, you will need a cable with a patch panel
Page 2
connector on one end and a male EIA connector on the other end.
2.0 NORMAL PIN BEHAVIOR
Different modem arrangements will show different signals. The
following pins should always be lit for continuous carrier full
duplex synchronous modems:
Name Number
DSR 6
TC 15
RC 17
DTR 20
DCD 8
The following pins flash when data is being transferred:
Name Number
TD 2
RD 3
RTS 4
CTS 5
By knowing what should happen when a line is first turned on or
plugged in, and using the breakout box, one can often isolate a
problem to the failing componenet.
First, check the modem control signals at both modems. Insure
that they reflect your understanding of the operation of the
modems you have.
When a line first starts, the two systems exchange DDCMP messages
to insure that 2 way communication is possible. Each line sends
the START message every few seconds until it gets a response. To
isolate a fault, after checking the modem control signals, look at
the breakout box at the first system. If the transmit lit blinks
every few seconds, then the device on this system is sending the
DDCMP START message. If the transmit light is not blinking, the
device or software is not working correctly. If the receive light
is blinking every few seconds, then the remote is sending the
DDCMP START message.
Repeat this test at the other system. The status of the blinking
send and receive lights should tell you whether the software and
the comm devices are sending DDCMP START messages, and if so, if
the messages are making it through the common carrier system.
Page 3
3.0 EIA PIN DEFINITIONS
For your convenience, here is a list of all 25 EIA pins.
+----------------------------------------------------------------+
| Pin| Name |To To | Function | Circuit |
| | |DTE DCE| |(CCITT) (EIA) |
|----+------+-------+----------------------------+-------+-------|
| 1 | FG | | Frame Ground | 101 | (AA) |
| 2 | TD | > | Transmitted Data | 103 | (BA) |
| 3 | RD | < | Received Data | 104 | (BB) |
| 4 | RTS | > | Request To Send | 105 | (CA) |
| 5 | CTS | < | Clear To Send | 106 | (CB) |
| 6 | DSR | < | Data Set Ready | 107 | (CC) |
| 7 | SG | | Signal Ground | 102 | (AB) |
| 8 | DCD | < | Data Carrier Detect | 109 | (CF) |
| 9 | | < | Positive DC Test Voltage | | |
| 10 | | < | Negative DC Test Voltage | | |
| 11 | | | Unassigned | | |
| 12 | SDCD | < | Sec. Data Carrier Detect | 122 | (SCF) |
| 13 | SCTS | < | Sec. Clear To Send | 121 | (SCB) |
| 14 | STD | > | Sec. Transmitted Data | 118 | (SBA) |
| 15 | TC | < | Transmitter Clock | 114 | (DB) |
| 16 | SRD | < | Sec. Received Data | 119 | (SBB) |
| 17 | RC | < | Receiver Clock | 115 | (DD) |
| 18 | | > | Receiver Dibit Clock | | |
| 19 | SRTS | > | Sec. Request To Send | 120 | (SCA) |
| 20 | DTR | > | Data Terminal Ready | 108.2| (CD) |
| 21 | SQ | < | Signal Quality detect | 110 | (CG) |
| 22 | RI | < | Ring Indicator | 125 | (CE) |
| 23 | | > | Data Rate Select |111/112|(CH/CI)|
| 24 | (TC) | > | External Transmitter Clock | 113 | (DA) |
| 25 | | > | Busy | | |
+----------------------------------------------------------------+
[End of BREAKOUT-BOX.MEM]