Honeywell CIPer 50 Installation & Commissioning Instructions page 10

CIPer MODEL 50 CONTROLLER – INSTALLATION & COMMISSIONING INSTRUCTIONS
RS485-2 (+)
RS485-2 (-)
Fig. 17. RS485-2 bias and termination resistors
NOTE: GND-2 is internally connected with 24V-0
(terminal 1)
RS485 Standard
According to the RS485 standard (TIA/EIA-485: "Electrical
Characteristics of Generators and Receivers for Use in
Balanced Digital Multipoint Systems"), only one driver com-
municating via an RS485 interface may transmit data at a
time. Further, according to U.L. requirements, each RS485
interface may be loaded with a max. of 32-unit loads. E.g.,
WEBs devices have as little as ¼ unit load each, so that up
to 128 devices can be connected.
BACnet MS/TP connections to the RS485 interfaces must
comply with the aforementioned RS485 standard. Thus, it
is recommended that each end of every connection be
equipped with one termination resistor having a resistance
equal to the cable impedance (120 Ω / 0.25 – 0.5 W).
RS485 systems frequently lack a separate signal ground
wire. However, the laws of physics still require that a solid
ground connection be provided for in order to ensure error-
free communication between drivers and receivers – unless
all of the devices are electrically isolated, and no earth
grounding exists.
IMPORTANT
In the case of new CIPer Model 50 controller
installations, we strongly recommend using a
separate signal ground wire. Doing otherwise may
possibly lead to unpredictable behavior if other
electrically non-isolated devices are connected and
the potential difference is too high.
In the case of the installation of CIPer Model 50
controllers in already-existent RS485 two-wire
systems (e.g., when replacing Spyder and Stryker
controllers with CIPer Model 50 controllers), not
using a separate signal ground wire will probably
have no undesirable effects.
The cable length affects the communication rate. Table 6
provides a few examples.
31-00233EFS-01
+5V
550 OHM
30
130 OHM
31
550 OHM
GND-2
Table 6. Bit rate vs. max. cable length for RS485
Bit rate
9.6 - 76.8 kbps
*115.2 kbps
* In the case of configuration of RS485-2 for Panel Bus,
the communication rate is set to 115.2 kbps.
For information on wire gauge, max. permissible cable
length, possible shielding and grounding requirements,
and the max. number of devices which can be connected to
a bus, refer to standard EIA-485.
Modbus Connection
The CIPer Model 50 controller can function as a Modbus
Master or Slave. In general, the RS485 wiring rules must be
followed.
Wiring Topology
Only daisy-chain wiring topology is allowed.
MODBUS MODBUS
MASTER SLAVE
Fig. 18. Allowed Modbus wiring topology
Other wiring topologies (e.g., star wiring, or mixed star
wiring and daisy chain wiring) are prohibited; this is to avoid
communication problems of the physical layer.
MODBUS MODBUS
X
MASTER SLAVE
MODBUS
SLAVE
MODBUS
SLAVE
Fig. 19. Prohibited Modbus wiring topology (example)
Cables
See also section "EIA 485 Cable Specifications" on pg. 30.
Use shielded twisted pair cable 3322 or 3251.
You must use three wires:
• One wire for D1 = Modbus +
• One wire for D0 = Modbus –
• One wire for the signal common
When using one pair for D1 and D0 and one wire of another
pair for the signal common, CAT5 cable may also be used.
10
Max. cable length (L)
3600 ft
2400 ft
MODBUS
SLAVE
MODBUS
SLAVE
MODBUS
X
SLAVE
MODBUS
SLAVE
MODBUS
SLAVE
MODBUS
SLAVE