The Gr 2400 Bus And Rs485 Communications Protocol - Lighting Controls Blue Box LT Series Installation, Operation & Maintenance Manual

30 THE BLUE BOX LT MAKING UP CAT. 5 CABLE WITH RJ45 CONNECTORS
INTRODUCTION (Continued)
THE GR 2400 BUS AND RS485
COMMUNICATIONS PROTOCOL
LC&D devices communicate using a method known sim-
ply as half duplex RS485 . This data communication meth-
od uses one twisted pair of the stranded Cat . 5 cable to
transmit data; and the other three pairs to carry power to
the switches .
All devices are connected in a single line (or bus) . This
RS485 network allows multiple items on a bus to be con-
nected in parallel, also called "Daisy Chain" wiring .
Each item on our system has two RJ45 jacks that allow the
cabling to come in on one side and go out the other .
To illustrate the "daisy chain" method, Figure 1 . 3 shows a
diagram of an LC&D GR2400 lighting control system .
One can see how a bad connection, say at the digital
switch, can prevent communication from the Master Panel
/DTC from reaching the rest of the bus .
Small imperfections in the Cat . 5 cable crimps tend to be
the most common "bad connections . "
GR 2400
Uplink Card
™
GR 2400 Master Panel
™ Master Panel
Chelsea
DigitalSwitch
Though a single imperfection may only slow down the
communication by a small margin it gets multiplied up
over the length of the chain .
RJ45 connectors simplify the wiring and connections of
our system, but the importance of having a good crimp
is paramount .
GR 2400 Slave Panel
™
™
GR 2400 Slave Panel
Figure 1.3
SmartBreaker
Panel
MicroPanel
™
SmartBreaker Panel
™