Table 2: Modbus RTU Rules Table
Rules/Maximums Allowed
Category
One direct Modbus RTU (RS-232) connection to the RS232C port is supported.
Connection of an RS-232/RS-485 converter to the RS232C port supports up to 32 Modbus
(RS-485) devices.
FC port does not support Modbus integration.
General
RS232C port supports one Modbus RTU (RS-232) device.
RS232C port with RS-232/RS-485 converter supports up to 32 Modbus (RS-485) devices.
Number of Devices
RS-232 cable length can be up to 15 m (49.2 ft).
RS-485 cable length can be up to 1,520 m (4,987 ft).
Cable Length
RS-232 stranded cable, 3-9 conductors, serial data grade, 20–24 AWG
RS-485 stranded cable, 0.6 mm (22 AWG) 3-wire twisted, shielded cable is recommended.
Stranded 0.6 (22 AWG) 4-wire (two twisted pairs) shielded is acceptable.
Cable
RS-232: requires no termination.
RS-485: End-of-line (EOL) termination must be set to On (or an EOL terminator installed) on the
two devices located at either end of each bus segment on an RS-485 bus. The EOL switches
must be set to Off (or EOL termination disabled) for all other devices on the bus segment on an
RS-485 bus.
Termination
Table 3: MSTP FC Bus Rules Table
Rules/Maximums Allowed
Category
One FC Bus with up to 32 MS/TP devices (on NIE296x models only)
Note:
An FC port on an NIE296x can connect to only one bus segment on an FC Bus.
Only a daisy-chain topology is allowed (no T or Star topology configurations).
General
Supports up to 32 MS/TP controllers on a single FC Bus segment.
Number of Devices
FC Bus can be up to 1,520 m (4,987 ft) using 0.6 mm (22 AWG) 3-wire twisted, shielded cable
.
When using fiber-optic connections: 2,010 m (6,594 ft) between two fiber-optic modems
Cable Length for FC Bus
Stranded 0.6 mm (22 AWG) 3-wire twisted, shielded cable is recommended.
Stranded 0.6 mm (22 AWG) 4-wire (two twisted-pairs) shielded cable is acceptable.
Note:
The + and - bus leads should be a twisted pair. On applications using 4-wire (two
twisted-pairs) cable, isolate and insulate unused conductor. Refer to the
MS/TP
Communications Bus Technical Bulletin (LIT-12011034)
for more information.
Cable
The EOL switch must be set to
On
(or an EOL terminator installed) on the two devices located
at either end of each bus segment on an FC Bus. The EOL switches must be set to
Off
(or EOL
termination disabled) for all other devices on the bus segment on an FC Bus. See
for information on setting the NIE EOL switch.
EOL Termination on the FC
Bus
1
If third-party devices are connected to the bus, the cable lengths should be reduced (if necessary) to match the third-party
vendor recommendations.
15
NIE29 Installation Instructions
