Data Bus Physical Specifications And Cable Requirements - Distech Controls ECLYPSE APEX User Manual

Modbus RTU Communication Data Bus Fundamentals
Baud: Auto (Factory Default) Baud: Auto (Factory Default)
Typical Modbus RTU Typical Modbus RTU
Device
EOL ON
Figure 130: Setting the Baud rate on two Controllers on a Modbus RTU Data Bus Segment for Failover Protection
Set the Modbus network communication parameters with EC- gfx Program in the Resources Configura-
tion window, Modbus Device block.
Figure 131: Setting the Modbus Network Communication Parameters in EC-gfxProgram's Resources Configura-
tion Window
See the EC- gfx Program User Guide for more information.
Data Bus Physical Specifications and Cable
Requirements
Cables composed of stranded conductors are preferred over solid conductors as stranded conductor
cable better resist breakage during pulling operations. Distech Controls strongly recommends that the
following data bus segment cable specifications be respected.
Parameter
Media
Shielding
Shield grounding
Characteristic impedance
Distributed capacitance between
conductors
Distributed capacitance between
conductors and shield
Maximum length per segment
Data Rate
Polarity
Multi-drop
EOL terminations
Data bus bias resistors
Table 29: Modbus RTU Data Bus Segment Physical Specifications and Cable Requirements
158
Baud: Auto (Factory Default)
Typical Modbus RTU
Device Device
EOL OFF EOL OFF
Data Bus: Shielded Twisted Pair Cable
Details
Twisted pair, 24 AWG.
Foil or braided shield
The shield on each segment is connected to the electrical system ground at one point
only; see Data Bus Shield Grounding
100-130 Ohms. The ideal is 100-120 Ohms
Less than 100 pF per meter (30 pF per foot). The ideal is less than 60 pF per meter (18pF
per foot)
Less than 200 pF per meter (60 pF per foot)
1220 meters (4000 feet)
9600, 19 200, 38 400, and 76 800 baud
Polarity sensitive
Daisy-chain (no T-connections)
120 ohms at each end of each segment
When VCC=5V: 510 ohms per wire (max. of two sets per segment)
When VCC=3.3V (The APEX is 3.3V internal): 330 ohms per wire
Baud: 38 400
Baud: 38 400
Typical Modbus RTU
ECLYPSE
Device
EOL OFF
Requirements.
RS-485
- S
Data Bus Shield
Connect to the 'S'
terminal
Electrical
System
Ground
ECLYPSE APEX