Troubleshooting
Problem
Clients often struggle to check and interpret data using the ModScan tool due to limited knowledge of Modbus registers and settings. As a result, they face difficulties validating this data against readings displayed in their SCADA system.
ModScan Main Screen (Before Configuration) – Shows the default ModScan interface.
Symptom
Values in ModScan do not match the readings shown in SCADA.
ModScan shows timeouts, invalid responses, or no data at all.
Raw register values appear incorrect or unreadable.
ModScan Register Read Showing Invalid Values – Highlights raw or scaled values that don’t match expectations.
Cause
Lack of understanding of Modbus addressing, data types, and scaling factors.
Incorrect configuration of ModScan parameters such as slave ID, baud rate, IP, or function codes.
Limited awareness of how raw Modbus values correspond to processed values shown in SCADA.
Mismatch between device register mapping and SCADA configuration.
Device Connection / ModScan Connection Settings – Shows COM port or TCP/IP setup for the device.
Environment
ModScan32 tool installed on a Windows-based engineering or commissioning laptop.
Connection to the field device/PLC via Modbus RTU (serial) or Modbus TCP (Ethernet) as per site configuration.
SCADA system running on the same network or connected to the same Modbus device for data validation.
Availability of the device’s Modbus register map and communication settings (baud rate, parity, slave ID, IP, etc.)
Diagnosing The Problem
Verify communication settings (Slave ID, baud rate/IP, parity, function code) in ModScan to ensure they match the device’s specifications.
Read the target registers in ModScan and compare raw values with the device’s Modbus register map to confirm correct addressing and scaling.
Cross-check values between ModScan and SCADA, identifying any mismatches that may indicate configuration or mapping errors.
Check for communication faults such as timeouts or unstable readings, which may point to wiring, network, or protocol issues.
- The minimal information required for ModScan data verification includes accurate Modbus mapping details, a ModScan update tool that isn't affected by polling time, and ensuring that the number of polls matches the number of responses. Attached are the mapping snippets, which highlight the minimal details required: IP address, Device ID, and the register where the data will be populated.
Resolving The Problem
Correct the ModScan configuration by aligning communication parameters (baud rate/IP, parity, stop bits, slave ID, function codes) with the device’s settings.
Ensure proper Modbus register mapping: apply -1 offset in addresses if required, select the correct data type, and confirm the LSB/MSB order.
Gather complete Modbus mapping details from the client, including register addresses, scaling factors, and expected ranges, to validate against SCADA.
Fix SCADA tag configuration to match the updated register map and data types, ensuring consistent values between ModScan and SCADA.
Resolve communication issues by checking wiring, network paths, COM port availability, or TCP connectivity for stable and error-free data exchange.
Testing should be done on the local machine where the Maximo Renewables service is running, ensuring real-environment conditions such as network paths, permissions, connectivity, Modbus mapping accuracy, register response validation, and successful ModScan communication with the device.
Support Case: If all checks pass but data still does not update in Maximo Renewables Portal, open a support case with IBM, providing details of all diagnostic steps taken.
Document Location
Worldwide
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Document Information
Modified date:
27 November 2025
UID
ibm17252380