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brkout.rno
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! d i g i t a l ! I N T E R O F F I C E M E M O R A N D U M
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Date: 20-January-82
From: TSG/NCSS
Loc: MR1-2/H22
Ext: HOTLINE 5911
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Subj: Use of a Breakout Box
.subtitle Subj: Use of a Breakout Box
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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.
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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.
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In either case, a quick check of the line using a breakout box may
be helpful if you suspect that the modems or the lines
themselves may be at fault.
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.hl 1 INSTALLING THE BREAKOUT BOX
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The breakout box is hooked into the line between the line driver
and the modem. 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.
.hl 1 TROUBLE SHOOTING
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To determine if the character is being received and transmitted
by the line driver(interface), watch the TD and RD lights on the break
out box while characters are being typed on the terminal. If the TD and
RD lights both blink, the character is making it through the common
carrier system to the CPU and being sent back to the terminal.
If the TD light blinks and the RD light does not, the character is
making it to the CPU but is not being sent back. This could mean a bad
interface or malfunctioning software.
If the TD light does not blink, the character is not making it
through the common carrier system. Install the breakout box at the other
end of the line between the terminal and the modem. Now look at the TD
and RD lights on the break out box. If the TD light blinks, the
character is being sent by the terminal but is not making it through
the common carrier system. This means malfunctioning modems or common
carrier. If the TD light does not blink, the terminal is not sending the
character and you have a bad terminal.
.hl 1 EIA PIN DEFINITIONS
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For your convenience, here is a list of all 25 EIA pins.
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| 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 | | |
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