Table 5: Guidelines for N2 network topology
Category
Rules and Maximums
Only daisy-chained devices (with maximum stub length of 3 m [10 ft] to any
device).
Number of
Devices
Up to 100 N2 devices supported per bus, with no more than two repeaters
between network engine and any N2 device and a maximum of 50 devices
between repeaters.
1,500 m (5,000 ft) twisted pair cable without a repeater
4,500 m (15,000 ft) twisted pair cable from NAE55 and the farthest N2 device
(three segments of 1,500 m [5,000 ft] each, separated by repeaters)
Line Length and
Type
2,000 m (6,600 ft) between two fiber modems
Cable
Solid or stranded 1.0 mm (18 AWG) 3-wire is recommended.
Solid or stranded 0.5 mm (24 AWG) larger 3-wire or 4-wire (two twisted-pairs) is
acceptable.
Note:
Use only twisted pair wire. On applications using 4-wire (two twisted-
pairs) cable, isolate and insulate unused conductor.
Terminations
Preferred Termination Configuration
: Two N2 devices with EOL switches in the
ON position, one at each end of each N2 Bus segment
Minimally Required Termination Configuration
: At least one N2 device with an
EOL switch in the ON position somewhere on each N2 Bus segment
Table 6: Modbus RTU rules
Category
Rules and Maximums
General
One direct Modbus RTU (RS-232) connection to the RS232C B port is
supported.
Connection of an RS-232/RS-485 converter to the RS232C B port supports up
to 32 Modbus (RS-485) devices.
FC-A and FC-B support one Modbus RS-485 integration.
Number of Devices RS232C B port supports one Modbus RTU (RS-232) device.
RS232C B port with RS-232/RS-485 converter supports 32 Modbus (RS-485)
devices or more, depending on the converter used.
Note:
The typical maximum Modbus device count between repeaters
is 32. Supported Modbus RTU serial device count may be limited
by manufacturer, cable, and communication speed. Check with the
manufacturer for more information.
Cable Length
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
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
acceptable. Standard wiring qualified for use with the N2 Bus or FC Bus is
acceptable.
Stranded 0.6 (22 AWG) 4-wire (two twisted pairs) shielded is acceptable.
23
NAE55/NIE55 Installation Guide
