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REXDESK: start and stop logging with triggers

Updated 22 Oct 2026

Make a REXGEN record only around the events you care about. A trigger starts or stops logging on a message, a signal value, a fault counter or a switch.

How triggers work

A trigger watches the bus or an input for a condition. When the condition becomes true, the trigger starts or stops logging. If you set a pre-trigger time, the logger keeps a rolling buffer of that length. The file then also holds what happened immediately before the event. After the event, the logger records for the log time you set, or continuously.

Pre-trigger time, the trigger event and the log time after the first or the last event.

Trigger window

Select Triggers on the toolbar, or Project > Triggers, to open the Triggers window.

The empty Triggers window with New Trigger, Edit Trigger and Delete Trigger buttons, a list with Active, Trigger Name and Trigger Description columns and a Current Trigger area below — The trigger list for the current project.

New Trigger: Creates a trigger.
Edit Trigger: Edits the selected trigger.
Delete Trigger: Deletes the selected trigger.
Current Trigger: A short description of the selected trigger.

Trigger settings

Select New Trigger. The first page, Select Trigger Action, sets what the trigger does. Select Next to go to Select Trigger Type.

Two pages of the new trigger wizard: Select Trigger Action with Trigger Name, Trigger Action Start Logging, Logger Initial State, New Log On Event, Log Time, Pre-Trigger Time and Debounce; and Select Trigger Type with the bus and four trigger types — The action page on the left, the type page on the right.

Trigger Name: A name for the trigger.
Trigger Action: Start Logging or Stop Logging.
Logger Initial State: Whether the logger is logging before the trigger fires.
New Log On Event: Starts a new log file for every event.
Log Time (sec): How long the logger writes after the trigger. 0 means continuous logging. Above 0, choose when the log time counts from. After the first trigger event logs for that time after the first event only. After the last trigger event starts at the first event and stops that time after the last one.
Pre-Trigger Time (sec): How much data from before the event the file keeps. 0 means no pre-trigger data.
Debounce (msec): For digital inputs: how long the logger ignores further changes after the first, so a bouncing switch counts once.

On Select Trigger Type, choose the Bus and one of the four trigger types below, then select Next.

Trigger conditions

CAN identifier

Trigger by CAN Ident fires when the logger receives a frame with the identifier you set. Enter it in CAN Ident or select it from a DBC file.

Signal value

Trigger by Parameter Value fires when a signal meets a condition. Import the signal from a DBC, then set the Operand and the Value.

The Define Trigger Condition page for a CAN identifier, with a DBC message list and a CAN Ident box — Trigger on a CAN identifier.

The Define Trigger Condition page for a parameter, with a DBC signal list, an Operand list and a Value box — Trigger on a signal value.

J1939 DM1 counter

Trigger by DM1 J1939 Counter fires when the DM1 fault counter Increases, Decreases or Changes. Tick Source Address to watch the DM1 messages of one ECU only.

Digital channel

Trigger by Digital Channel fires when a digital input Rises, Falls or Changes. It is available only when the configuration contains a digital input, as in the next section.

The Define Trigger Condition page for a DM1 counter, with the list open on Increases, Decreases and Changes and a Source Address tick box — Trigger on the J1939 DM1 counter.

The Define Trigger Condition page for a digital input, with Channel 0 selected and the list open on Rises, Falls and Changes — Trigger on a digital input.

Select Next and save the trigger. When a configuration holds a trigger, the Storage button under Device Configuration changes to show it. Select Run to send the configuration.

Digital input trigger

This section applies to every REXGEN except REXGEN 1, which has no digital inputs. Digital inputs idle high. Wire the switch between the input pin and ground. Closing the switch pulls the input low, which is a falling edge. Find the pin in the pinouts guide for your logger. For wiring, see REXDESK: log analogue and digital inputs.

Add the digital input. Drag Dig In onto the Channels area. Choose the channel and the sampling rate, then select Add.
Create the trigger. Open Triggers and select New Trigger. Set Trigger Action to Start Logging, enter the Pre-Trigger Time and the Debounce, and a Log Time if you want one, then select Next.
Choose the edge. Select Trigger by Digital Channel and the channel. For a switch to ground, choose Falls or Changes. A Rises trigger needs a circuit that holds the input low until the event.
Save and send. Select Next and save the trigger. Then select Run to send the configuration to the logger.