Specifications

Niagara Release 2.3
Revised: May 22, 2002 Niagara Networking & Connectivity Guide
Chapter 2 Configuration and Troubleshooting Tools
Niagara Configuration Tools
2–12
About Serial and
Null Modem
Cables and
Adapters
The standard RS-232C serial communications interface defines a signal protocol
used between data terminal equipment (DTE) (such as your engineering PC) and a
data communications equipment (DCE) (such as a modem).
The protocol signals are transmitted on a set of lines within the standard serial cable.
Two lines (RXD and TXD) are used for sending and receiving data. They provide a
full duplex connection between the two devices (the data can be transmitted in both
directions simultaneously). Two more lines (CTS and RTS) form a flow control pair
that is typically used to throttle the communication flow on the transmit and receive
lines. The last pair of lines (DTR and RTS) is typically used for a connection
true/false instead of character data flow.
JACE-5
Since the serial connection on a JACE-5 is DTE, a standard serial cable cannot be
used to connect it to the DTE serial port on your PC. When you need to connect two
DTE devices together a null modem cable is used instead. A null modem makes the
other end of a DTE connection look like a DCE connection.
Standard serial and null modem cables are widely available commercially.
JACE-4
The serial port on a JACE-4 is also DTE, however the serial connection on the
JACE-4 is RJ-45, and not the standard DB-9. It was designed this way because a
DB-9 connector does not fit through a standard 1/2-inch knockout hole, and because
wiring a RJ-45 connector is easier than wiring a DB-9 connector. In addition, the
RJ-45 connector will pass through a conduit fitting so that if conduit is a requirement
on the installation, it may not be necessary to cut the terminations off a ready made
cable.
The cable used between a JACE-4’s serial port and another DTE or DCE device is
8-conductor flat, silver satin stranded cable with the addition of an RJ-45 (female) to
DB-9 (female) adapter. Note that silver satin cable is not the standard Ethernet cable,
in which the pairs are twisted around each other. When used with the JACE-4, the
twisting of the pairs may cause undesirable effects on the serial communication,
therefore we recommend the use of flat silver satin cable instead.
Similar to the standard Ethernet twisted pair, however, the silver satin cable should
be wired straight through (see the “About Ethernet Straight Through and Crossover
Cables” section on page 3-10). When connecting to a DCE device, the RJ-45 to DB-9
adapter is also pinned straight through.
To connect a JACE-4 to another DTE device, such as your PC, you can use a
silver-satin straight-through cable and a null-modem adapter, or wire the silver-satin
in a null modem configuration and use a straight through adapter (see “Wiring a
Silver Satin Null Modem Cable,” page 2-14).