Installation manual

Appendix B - Hardware Specifications 61
Cyclades-TS Installation Manual
servers use RJ-45 connectors for serial communication. Unfortunately there is no standard RS-232 pin assignment
for RJ-45 connectors. Every equipment vendor has its pin assignment.
Most connectors have two versions. The ones with pins are said to be “male” and the ones with holes are said to
be “female”.
RS-232
Signal
Name/Function
(Input/Output)
DB-25 pins
(Standard)
DB-9 pins
(Standard)
RJ-45 pins
(Cyclades)
Chassis Safety Ground 1 Shell Shell
TxD Transmit Data (O) 2 3 3
RxD Receive Data (I) 3 2 6
DTR Data Terminal Ready (O) 20 4 2
DSR Data Set Ready (I) 6 6 8
DCD Data Carrier Detect (I) 8 1 7
RTS Request To Send (O) 4 7 1
CTS Clear To Send (I) 5 8 5
Straight-Through vs. Crossover Cables
The RS-232 interface was originally intended to connect a DTE (computer, printer and other serial devices) to a
DCE (modem) using a straight-through cable (all signals on one side connecting to the corresponding signals
on the other side one-to-one). By using some “cabling tricks”, we can use RS-232 to connect two DTEs as is
the case in most modern applications.
A crossover (a.k.a. null-modem) cable is used to connect two DTEs directly, without modems or communication
lines in between. They data signals between the two sides are transmitted and received and there are many
variations on how the other control signals are wired. A “complete” crossover cable would connect TxD with
RxD, DTR with DCD/DSR, and RTS with CTS on both sides. A “simplified” crossover cable would cross TxD
and RxD and locally short-circuit DTR with DCD/DSR and RTS with CTS.
Which Cable Should be Used
First, look up the proper cable for your application in the table below. Next, purchase standard off-the-shelf