RS-485

1
RS-485
INCOM
Because different frequencies are delayed and
attenuated by different amounts, a waveform rich
in harmonics is distorted after passing through
an LC circuit.
On the contrary, a pure sinusoid, while delayed
and attenuated, keeps its original waveshape
after passing through an LC circuit.
2
Detecting RS-485 1s and 0s
Receivers than convert serial bit streams into
parallel data are called UARTs (Universal
Asynchronous Receiver Transmitters). A UART
determines whether the serial stream contains a 1
or a 0 by sampling at the bit rate (9600, 19.2 k,
etc.) For better error immunity it typically
samples 2 or 3 times per bit. Two bit readings
in a row must be the same for the UART to declare
a 1 or a 0. With distorted wave shapes, the UART
will typically be observing a data stream where
the bit value changes from within a bit
time. This can cause the UART to declare various
errors (such as framing or parity) and discard
the byte.
3
INCOM Decoding
Since the waveshape is not changed, it is still
easy to detect the difference between a 1 and 0
from an Frequency Shift Keyed (FSK)
signal. INCOM signals are not as affected by
impedance mismatches (taps, Ts, Ys, etc.).
Consequently the cabling rules are more relaxed
than with RS-485.
4
Excerpt (Page 33) from RS-485Based Installation
Manual
5
Noise Immunity
RS-485
Since RS-485 decides if a signal is a 1 or a 0 by
examining the amplitude, external events can mask
the true value.
INCOM
INCOM FSK uses a bandpass filter to eliminate
signals substantially above or below 100 kHz.
Therefore large amplitude interfering signals
removed
6
INCOM Vs RS-485
7
A
B
C
D
E
F
G
H
I
J
1
1
Cutler-Hammer IMPCABLE or Belden 9463 (or
equivalent in Plenum)
RJ-11
CONI
Install in PC
This design places brings all network (Lighting
Control and Power Monitoring) back to the Central
Plant.
RJ-45
IN 1
IP 2
Shield 3
Phoenix Contact RJ-11 to Terminals
Ethernet Hub
Ethernet 10BASE-T
RS-232
2
2
Belden 9207 (or equivalent in Plenum)
RS-485/ 232
200 max
Typical Switchboard Tap
RS-485 Device
To PDS
PONI
PONI
130
131
3
3
IED
IED
IED
Typical
Typical
IQ Analyzer
IQ Analyzer
4
4
PONI
131
5
5
These taps are legal with INCOM wiring. These
are not legal with RS-485
IED
RS-485 Network
INCOM Network
Typical
IQ Analyzer
6
6
Parking Garage
Terminal
Parking Lot
RS-485 Network
7
THE INFORMATION ON THIS DRAWING IS THE PROPERTY
OFEATON CORPORATION. IT IS DISCLOSED IN
CONFIDENCEAND IS NOT TO BE REPRODUCED, USED OR
DISCLOSEDEXCEPT FOR THE PURPOSE FOR WHICH
FURNISHED.
DFTR
DATE
1
APPD
DATE
CUTLER-HAMMER
DGL
11-DEC-98
APPD
DATE
POWER MANAGEMENT PRODUCTS CENTER
ENG. REF.
DATE
TITLE
REVISION
NEXT REF.
DATE
8
SHEET NO
DWG NO
SIZE
SCALE
DIRECTORY
1 OF 1
A
NONE
A
B
C
D
E
F
8
RS-485 and INCOMWiring Rules
200feet
200feet
200feet
200feet
Total Cable Length ? to ? 13 x 200 2600
feet Conduit space required sufficient for 2
twisted pairs
200 feet
?
200 feet
200 feet
200 feet
?
RS-485 Node
RS-485 Node
RS-485 Node
RS-485 Node
RS-485 Node
200feet
200feet
200feet
200feet
Total Cable Length ? to ? 9 x 200 1800 feet
(70 of the RS-485 system) Conduit space
required sufficient for 1 twisted pairs
?
200 feet
200 feet
200 feet
200 feet
?
IQ Node
IQ Node
IQ Node
IQ Node
IQ Node
9
Excerpts (Page 34) from RS-485 Based
Installation Manual