Tips For Correcting Bus Installation Problems - Johnson Controls MS-FIT100-0 User Manual

Tips for Correcting Bus Installation Problems

The MS/TP Bus is subject to a number of installation factors that can affect performance. Consider
the following common physical attributes when trying to resolve communication problems:
• Validate controller/device power is available and undisrupted.
• Check wiring for:
- - Proper wire gauge, cable type, connections, polarity, and lengths.
- - Opens and shorts.
- - Confirmation that one shield ground point exists per bus segment (made at the source of
the bus segment —the NAE, Side B of a Repeater).
• Check EOLs to verify that EOL terminations are only at the ends of daisy chains for each bus
segment.
• Check addresses for:
- - duplicate addresses
- - address ranges are sequential
• Check for and eliminate T-Taps (wire configurations that create a T shape) and star
configurations.
• Check for consistent baud rates (often baud rates problems occur with vendor devices and
repeaters).
• Check for sources of electrical interference.
Here are some additional best practices to find and eliminate problems with the physical layer:
• Check and confirm proper idle voltage levels on each bus segment. See
Levels
for more information.
• Separate the bus into smaller segments to isolate and find problems.
• Check idle voltage levels on these smaller segments.
• Use the FIT's 1-ON-1 modes on disconnected controllers to validate they have proper attributes
and are not defective. See
• Remove vendor equipment from the bus. Johnson Controls does not manage vendor equipment
communication or default states. Isolating a bus to devices with known defaults ensures effective
communication.
Getting Prepared to use the FIT
See
continuous bus wiring and end-to-end continuity.
32
1-ON-1 Menu for more information.
section for ways to use the tool on unpowered buses to validate
Voltage Menu
MS-FIT100-0 Field Inspection Tool User Guide
Voltage
and