Lighting Controls Blue Box LT Series - The GR 2400 Bus and RS485 Communications Protocol

30 THE BLUE BOX LT MAKING UP CAT. 5 CABLE WITH RJ45 CONNECTORS
LCDBBMUCAT03Sept08
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.”
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.
Figure 1.3
Uplink
™
Card
GR 2400
™
Master Panel
Chelsea
DigitalSwitch
™
GR 2400
™
Slave Panel
MicroPanel
™
SmartBreaker
™
Panel
GR 2400 Master Panel GR 2400 Slave Panel SmartBreaker Panel