Specifications

SA Bus Rules and Specifications
The SA bus connects IOMs, VSDs, and NS-Series network sensors to field controllers. Figure 11 shows three SA
bus examples. Table 7 and Table 8 provide SA bus rules and specifications.
Table 7: SA Bus Rules
Rules/LimitsCategory
Each bus supervisor supports one SA Bus (and each SA Bus is a single segment).General
An SA Bus supports up to 10 devices. The SA bus supervisor provides
power for all slave devices connected to the SA bus, including up to four
NS network sensors. IOMs connected to the SA bus are not powered by
the bus supervisor.
Note: Exceeding the SA bus power limit can result in devices going offline and
poor bus performance. See SA Bus Device Limits for more information
on SA bus power limits.
Number of Devices Supported on the Bus
SA Buses do not support repeaters.
365 m (1,200 ft) maximum bus lengthCable Length
152 m (500 ft) maximum distance between an NS network sensor and the bus
supervisor (FAC, FEC, or VMA16 supplying power to the sensor) using bus cable
connected to the SA Bus screw terminal blocks
30 m (100 ft) maximum length for network sensors using bus cables connected
to the RJ-Style modular jack (6-Pin SA Bus Port)
366 m (1,200 ft) maximum bus length
Screw Terminal Connections: 22 AWG Stranded 4-wire, 2-Twisted Pairs,
Shielded Cable for screw terminals.
Modular Jack Connections: 6-Pin RJ-Style Modular Connectors with 24 or 26
AWG Solid 6-Wire, 3 Twisted-Pairs
Recommended Cable Type
1
Each SA bus supervisor has integral (fixed ON) EOL termination, which typically
provides sufficient EOL termination on an SA bus. Long SA bus runs or persistent
communication problems on an SA bus may require EOL termination at the last
device on the SA bus (in addition to the integral EOL termination at the SA bus
supervisor).
EOL Termination
Do not mix RJ-style modular (phone) jack devices and screw terminal devices
on the SA bus.
Mixing Device Types
1
The recommended cable types provide the best bus performance. See MS/TP Bus Cable Recommendations for information
on alternative cable types.
Table 8: SA Bus Specifications
SpecificationCategory
Message Headers checked using 8-bit CRC test.
Message data check using 16-bit CRC test.
Error Checking
0–255 (See Device Addresses on the MS/TP Bus for more information.)
Device Addressing
RS485Data Transmission Standard
BACnet® MS/TPSignaling Method
9600; 19,200; 38,400 (default); or 76,800 baud as selected by the bus supervisorSignaling Rate
Meets EN61000-4-4 and EN6100-4-5 requirements for heavy industrial
applications. Protected against misapplication of 24 VAC.
Transient Immunity
One hard ground per bus segment when using shielded cableShield Grounding
Daisy-chained (screw terminal only).Physical Configuration
27MS/TP Communications Bus Technical Bulletin