Loopback connectors are designed for the testing of communication ports. They take the form of either a single plug or a port-to-port cable with some communication connections shorted (looped-back).
Loopback connectors must be wired properly and connected firmly for the Serial Port tests to work correctly. Miswired, poorly soldered, or missing loopback connectors can cause erroneous diagnostic error messages.
The table below depicts the pin assignments for most loopback plugs and cables that may be used when testing a system.
Table A-1 Loopback Connector Pin Assignments
Signal Description |
EIA |
CCITT # |
RS-449 "A" |
RS-449 "B" |
DIN 8 8-pin round |
DB9 9-pin |
DB25 25-pin |
Direction |
Alpha ID |
---|---|---|---|---|---|---|---|---|---|
Chassis/Frame Ground |
AA |
101 |
1 |
NC* |
NC* |
NC* |
1 |
none |
AA |
Transmit Data (TxDa) |
BA |
103 |
4 |
22 |
3 |
3 |
2 |
output |
BA |
Receive Data (RxDa) |
BB |
104 |
6 |
24 |
5 |
2 |
3 |
input |
BB |
Request To Send (RTSa) |
CA |
105 |
7 |
25 |
6 |
7 |
4 |
output |
CA |
Clear To Send (CTSa) |
CB |
106 |
9 |
27 |
2 |
8 |
5 |
input |
CB |
Data Set Ready (DSRa) |
CC |
107 |
11 |
29 |
NC* |
6 |
6 |
input/ output |
CC |
Signal Ground (SG) |
AB |
102 |
19 |
NC* |
4 |
5 |
7 |
none |
AB |
Data Carrier Detect (DCDa) |
CF |
109 |
13 |
31 |
7 |
1 |
8 |
input |
CF |
Transmit Clock In (TRxCa) |
DB |
114 |
5 |
23 |
NC* |
NC* |
15 |
input |
DB |
Receive Clock in (RTxCa) |
DD |
115 |
8 |
26 |
8 |
NC* |
17 |
input |
DD |
Data Terminal Ready (DTRa) |
CD |
108 |
12 |
30 |
1 |
4 |
20 |
output |
CD |
External Clock Out (TRxCa) |
DA |
113 |
17 |
35 |
NC* |
NC* |
24 |
output |
DA |
Secondary Data Carrier Detect (DCDb) |
SCF |
122 |
NC* |
NC* |
NC* |
NC* |
12 |
input |
SCF |
Secondary Clear to Send (CTSb) |
SCB |
121 |
NC* |
NC* |
NC* |
NC* |
13 |
input |
SCB |
Secondary Transmit Data (TxDb) |
SBA |
118 |
NC* |
NC* |
NC* |
NC* |
14 |
output |
SBA |
Secondary Receive Data (RxDb) |
SBB |
119 |
NC* |
NC* |
NC* |
NC* |
16 |
input |
SBB |
Secondary Request to Send (RTSb) |
SCA |
120 |
NC* |
NC* |
NC* |
NC* |
19 |
output |
SCA |
NC = No connection
The RS-232 and RS-423 single-port loopback plug is a specially wired male DB-25 connector. It is plugged in to a serial port in the back of the system under test. The wiring is shown in Figure A-1.
Use these wiring instructions for 25-pin RS-232 and RS-423 port to 25-pin RS 232 and RS 423 port loopback cables (two DB-25 connections). It is plugged into a pair of serial ports in the back of the system under test. Both connectors are male. The wiring is shown in Figure A-2.
Use these wiring directions for 8-pin round DIN RS-232 port to RS-423 to 8-pin round-DIN RS-232 and RS-423 port loopback cable (see Figure A-3). Both connectors are male.
Pin 8, Receive clock In (DD), remains unconnected.
Use these wiring directions for male 8-pin round-DIN RS-232 and RS-423 Single port loopback plugs (see Figure A-4).
Pin 8, Receive Clock In (DD), remains unconnected.
Use these wiring directions for a 25-pin Port A to Port B loopback plug for most systems (see Figure A-5).
If your system has a single communication port to connect it to peripherals, use these wiring instructions for making a male 25-pin loopback plug for that communication port (see Figure A-6):
This 96-pin connector (see Figure A-7) can be ordered from Sun Microsystems (Part Number 370-1366).
This 96-pin connector (see Figure A-8) can be ordered from Sun Microsystems (Part Number 370-1381).
Use these wiring instructions for a loopback cable for two 37-pin RS-449 synchronous ports (see Figure A-9).
Use these wiring instructions for making a male 37-pin RS-449 loopback plug (see Figure A-10). This connector is also available from Sun (Part Number 530-1430).
Use these wiring instructions for male 9-pin RS-232 and RS-423 single-port loopback plugs (see Figure A-11):
Use these wiring directions for female 9-pin RS-232 and RS-423 single-port loopback plugs (see Figure A-12):
Use this loopback plug with the pcmciatest.
Use these wiring instructions for a 9-pin RS-232 and RS-423 port to 25-pin RS-232 and RS 423 port loopback cables (see Figure A-13). Both connectors are male.
Use these wiring instructions for 9-pin RS-232 and RS 423 port to 9-pin RS-232 and RS-423 port loopback cables (see Figure A-14). Both connectors are male.
Please note that this cable has no Sun part number assigned to it.
Using two standard RJ45 connectors, and connect pin1 to pin1, pin 2 to pin 2, and so on, for all pins. This loopback is a "straight-through" connection.