Monitor: observing current communication
Monitor summarizes the latest values and communication state. Use Tracer to analyze message sequences and find events.
The source may be live traffic or a trace being played back. Source preparation and the difference between viewing and playback are described under passive observation.
Using Monitor
- Choose a profile and module, configure a connection to a line carrying traffic and open
Monitorin the sidebar. Monitor itself does not start device polling. - Find the CAN ID or Modbus
Unit IDgroup. Compare the latest CAN bytes or Modbus values,Period,AgeandCount. - Change the observed device's state and watch which values or bytes are highlighted.
- Use Tracer to investigate the request and response sequence.
Period describes message repetition; Age shows how long ago the row was last observed. If traffic stops, the last value may remain visible: increasing Age helps distinguish it from a fresh observation. Change highlighting and communication activity are different: a repeated response with the same value increases the count without changing the value itself.
Overall line load is available through the transport name in the status bar: see line utilization and transport statistics. It summarizes all physical traffic separately.
Modbus RTU
Rows are created from observed operations and grouped by device address. Within each device, operations differ by function, start address and element count.
| Element | Meaning |
|---|---|
Unit ID group | Device address |
Function | Function code and name |
Register(s) | Zero-based addresses of range elements |
Value(s) | Observed values opposite their corresponding addresses |
Period | Smoothed interval between observed requests for the same operation |
Age | Time since this row's latest observation |
Count | Number of observations; a request and its matching response increase it separately |
Displaying read values requires both the request and matching response. A read response does not contain its start address; without the request, Monitor does not assign it to an arbitrary range.
Registers are unsigned 16-bit values; discrete values are bits. Determine register meanings, scaling and compound value word order from the device documentation. Register pairs are not automatically interpreted as float32. All range elements are displayed, with one address and value per line within the cell. Changed values are highlighted individually. For function 05, the confirmed single value is displayed as the numeric response field: 65280 (0xFF00) means on, and 0 means off.
Status values
Hover over a row to see the result of its latest observation in a tooltip.
| Status | Interpretation |
|---|---|
Request observed | A request was observed; this does not yet confirm execution |
Response observed | A matching response was observed |
Write observed | A write was observed, but identical-looking request/response roles could not be established |
Broadcast observed | A broadcast request was observed; no response is expected |
Exception 0x… | An exception response arrived |
Response mismatch | A response does not match the expected request parameters |
Age and row fading do not prove a device timeout: normal infrequent polling also leaves long pauses. Observed period is not response time. After a new request, the row may still show its last received value: consider the tooltip and age. An exception response or parameter mismatch replaces values with —.
CANopen and Automotive VAG
CAN Monitor groups recurring frames by CAN ID, identifier format, RTR and CAN FD flags. The latest contents replace previous contents in the same row.
| Column | Meaning |
|---|---|
CAN ID | Frame identifier, possibly labeled from an available description |
Dir | Semantic direction hint based on known addressing; not a universal RX/TX indicator |
EXT, RTR, FD | Identifier format, remote request and CAN FD |
DLC | Displayed payload length in bytes |
MSG | Latest data bytes with change highlighting |
Period | Interval between the latest frames in this row |
Age | Time since this row's latest observed frame |
Count | Number of processed frames in this row |
Byte and bit highlighting helps identify reactions to input, switch position or bench state changes. Appearance and fading depend on highlight settings in Settings → Monitor → Dynamic highlight, shared by CAN and Modbus.
When DBC loading is available and a suitable file is selected, Monitor may also display decoded signals. This depends on the message descriptions. The current Monitor DBC decoding path uses the first 8 bytes; displaying a full CAN FD frame does not mean all 64 bytes are decoded through DBC.
CAN Monitor is not a table of every CANopen object or ECU parameter. Use device descriptions and the Protocol layer in Tracer for CANopen objects, and the corresponding messages on that layer for UDS/KWP2000.
Reset
Reset view in Modbus and Reset monitor in CAN clear the accumulated Monitor summary. They do not reset the device or erase a saved file. The Tracer filter does not change the Monitor summary.
Empty tables or unchanging values
- Check the module and connection: Monitor is populated only when traffic arrives.
- For Modbus, check Tracer for a request and its matching response. Read responses alone are insufficient to determine the register range.
- Watch
AgeandCount: a constant value with an increasing count can be normal. - Opening a file in Tracer does not by itself populate Monitor. Static viewing and playback are different.