Troubleshooting DMS-Microsmart Bus Communication Issues

[Product_Support]

Issue

Communication failures with Microsmart controllers on the DMS bus network.

Product Line

TAC IA Series

Environment

Microsmart controllers (all models installed with revision 9.x, 10.x, or 11.x firmware)

Cause

Common causes include:

• Incorrect power supply wiring or insufficient voltage
• Shared power between controllers and field devices
• Exceeding maximum controller count per RS-485 segment
• Improper network topology or cable type
• Missing or incorrectly installed End-of-Line (EOL) modules
• Ground loops or shield continuity issues
• Duplicate or illegal point names in controller database
• Faulty line drivers or incorrect address switch settings

Resolution

The following checklist provides several settings/configurations to review when faced with a communication problem at the controller level. The content was compiled from different resources, summarized, and laid out in an easy-to-use manner so as to provide a quick-reference document.

Do all controllers have a power supply? Each takes 24 VAC from a Class 2 transformer	ACTION: Confirm with a voltmeter. If no voltage present, check on-board fuse and then the local circuit breaker. Note: Do NOT ground the transformer’s secondary when powering a MSC-MPC-001. With other controller types, the secondary is grounded. If voltage is present, must be within tolerances (20.4 to 30 VAC) Confirm power (VA) requirements. Varies per controller (see installation instructions)
Do the affected controllers share a common power supply? The MSC-MPC-001 must have its own DEDICATED power supply Other controller types can share the same AC transformer provided the VA rating is adequate	ACTION: Review power wiring (see installation instructions)
Do the affected controllers share a common power supply with output field devices? Power for the controllers and power for the output devices MUST REMAIN SEPARATE	ACTION: Review controller and field device power wiring (see installation instructions) In addition, avoid wiring any half-wave and fullwave powered devices to the same transformer.
How many MicroSmart controllers exist? Firmware revision 9, 10, & 11 family controllers can communicate on the same RS-485 wire segment simultaneously Maximum per RS-485 segment = 30 (31 if no repeater is installed)	ACTION: Determine controller count If there are more than 31, a repeater/router is required If there are more than 62, only firmware revision 11 family controllers can be physically addressed higher than 62 Connect the first 30 controllers (isolate any additional nodes) and attempt/stabilize communications.
Any repeaters installed? Allows the connection of two or more RS-485 wire segments Extends the maximum controller count by 30 (maximum of 124 addressable nodes supported)	ACTION: Identify model number Review settings using its installation instructions Replace line drivers with known, good ones (Part# E21-1144)
How rapidly is the Watch Dog Timer (WDT) LED blinking? Once / second = proper network communication A controller’s logical address is always one higher than the number calculated by the switch settings. For example, if all switches are OFF (binary equivalent of 0), the controller’s logical address is 1. If switches 1 & 2 are ON (binary equivalent of 3), the controller address is 4. Network wire connections ARE polarity sensitive.	ACTION: Review LED activity No blinking but illuminated Verify proper power requirements & wiring (see installation instructions) Perform a hardware clear (place all address switches in the ON position and power cycle the controller) No blinking & not illuminated Check the on-board fuse Blinking faster than once / second Check the address switch for proper position. Verify address is not duplicated on the network Check the network connector and ensure it is properly inserted Ensure the + wire and – wire are properly identified and the shield wire is also connected.
What is the length and topology of the controller trunk? Bus Topology Daisy-chain (no tees) 4000ft/1219m maximum wire length Trunk wiring is polarity sensitive Recommended cable: 24 AWG twisted-pair, shielded General Purpose: Under 1000ft, Belden#9501 Over 1000ft, Alpha#9823C Plenum & Riser-Rated: Under 1000ft, Belden#89503 Over 1000ft, Belden#89182	ACTION: Review the following: Ensure two EOL modules are installed. Each module must be installed correctly (black dot on module in the same corner as the white dot on the circuit board) Remove each EOL and check for following resistances: Pins 1-8: 3.3 kohms Pins 3-6: 150 ohms Pins 4-5: 3.3 kohms Ensure there are no ground loops in the + and – wires. To do this, use a multi-meter & measure the + and – wires, separately to earth ground Ensure the shield wire is continuous throughout the entire length of the trunk and connected to a solid earth ground in only one location Replace line drivers on the controllers (Part# E21-661). Check trunk voltages: + to earth ground: 2.2 – 2.6 Vdc – to earth ground: 2.2 – 2.6 Vdc If 0 Vdc or 5 Vdc is detected, check other controllers for bad line drivers. Determine cable used. If it is shielded, connect it to earth ground in ONE location through a 470 kK, ¼ watt resistor. The shield must be continuous throughout the wire segment.
What is the condition of the controller database?	ACTION: Review the controller database Illegal point names must be corrected. Illegal characters are: / # * : ; $ = | &. Duplicate point names must be corrected
Will Operator Interface (Part# PS-OPRIF) communicate to the controller? Direct connection to a controller can only be done with the Firmware Revision 10 & 11 Families Accessing a networked controller through a direct connection using a MSC-LIM is possible but very slow (300 baud maximum). It is only recommended for checking communication status and not for application programming. It will also require a master controller (DMS35/350A/3500)	ACTION: Attempt an upload of the controller database Requires a Laptop Interface Module (Part# MSC-LIM) Operator Interface version 11.41 and 11.6 both support direct connection to a controller If communication fails to work, try another controller to eliminate the pc and interface cabling from the troubleshooting process