Texas Instruments TravelMate 4000M User Reference Manual page 249

Loopback Connections
The serial and parallel communications tests in the
Diagnostics Program offer optional loopback tests that
require placing loopback connectors on the output ports of
the computer. The loopback connector pin assignments are
listed in the following tables.
Loopback Connector Pin Assignments
Serial Loopback Connections
DB9 Pin Signal
1-7-8
CD-RTS-CTS
2-3
TX-RX
4-6
DTR-DSR
Parallel Loopback Connections
DB25 Pin
15-2
13-1
16-10
17-11
14-12
Signal
D0-ERR
STRB-SLCT
INIT-ACK
SLCTIN-BUSY
A
UTOFEED-PE
Diagnostics
Diagnostics D-11