Specifications

Appendix: Maximizing and Troubleshooting the MS/TP Bus
Maximizing Tips
Observe the following guidelines to maximize the performance of an MS/TP bus.
DescriptionGuideline
COV reports account for the highest amount of traffic on the bus. For best
performance, keep the COV rate at 500 COVs per minute or fewer for each network.
To reduce the COV traffic:
• Set the COV increment to the largest value that still provides acceptable
performance.
• Do not map more points to the NxE than are required.
For mapped analog points, where the values are changing frequently, consider the
following to limit COV reports:
• Increase the COV increment on the point.
Note: For some Analog Inputs (AIs), this value cannot be modified.
• Set the Use Cov Min Send Time flag to true, which causes the COVs to be
sent on a timed basis. The time value is specified in the controller device object.
Limit the Number of Change of Value
(COV) Report Rates over the MS/TP Bus
Slave devices on the FC bus are not supported. The SA bus only supports a specific
set of slave devices.
Do Not Place Slave Devices on the FC
Bus
Third-party devices can seriously degrade both hardware and software performance
depending on their quality and configuration. Consider and configure third-party
devices carefully according to the manufacturer’s specifications.
Carefully Evaluate Third-Party Devices
Once the system is configured, commissioned, and running, avoid adding extra
traffic to the bus by performing unnecessary auto-discovery operations, downloads,
or bus analysis.
Do Not Add Extra Traffic
Follow the wiring rules carefully. The tolerances of the MS/TP bus are tighter than
other, slower protocols may be. Improper terminations may result in errors causing
serious network degradation. See MS/TP Bus Cable Recommendations.
Observe the MS/TP Wiring Guidelines
See Statistics Attributes.
Check the MS/TP Statistics for Errors
Avoid changing default MS/TP bus settings, especially settings you may be unfamiliar
with. Some parameters set improperly or randomly can cripple the MS/TP bus
completely.
Use Default MS/TP Settings
MS/TP Bus Health Factors of the Diagnostics Tab
The Diagnostics tab of the MS/TP field bus integration, viewed from the Metasys system UI, provides a snapshot of
the condition of the bus. The attributes that are most illustrative of the bus condition are the Bus Health Index and
Bus Performance Index attributes, both located under Calculations (Figure 25). The Statistics attributes also provide
a useful look into the condition of the MS/TP bus.
47MS/TP Communications Bus Technical Bulletin: Appendix: Maximizing and Troubleshooting the MS/TP Bus