1 Trigger Overview

In the fields of machine vision, industrial cameras, and scientific imaging, a Trigger is a mechanism that controls when a camera starts image acquisition. Instead of continuous streaming in free-running mode, the camera performs exposure and image capture precisely at a specific moment based on external signals or internal conditions. This achieves high-precision synchronization with moving objects, light sources, PLCs, robotic arms, and other devices.

1.1 Why Trigger Is Required

• Avoid motion blur: Capture high-speed moving objects on conveyor belts.
• Save bandwidth and storage: Take images only when targets appear.
• Multi-camera synchronization: Multiple cameras capture the same event simultaneously.
• Sync with light sources: Expose exactly when the flash is triggered.
• Improve system determinism: Make image acquisition timing predictable.

1.2 Main Types of Camera Trigger

1.3 Key Trigger Configuration Parameters

2 Unique Trigger Mechanism of CoaXPress

<Enumeration Name="TriggerSource">
    <ToolTip>This feature defines the source of the trigger signal.</ToolTip>
    <Description>This feature defines the source of the trigger signal.</Description>
    <DisplayName>Trigger Source</DisplayName>
    <Visibility>Beginner</Visibility>
    <pIsLocked>IsRunning</pIsLocked>
    <EnumEntry Name="Software">
        <DisplayName>Software Trigger</DisplayName>
        <Value>0x0</Value>
    </EnumEntry>
    <EnumEntry Name="CXPTrigger">
        <DisplayName>CXP Trigger</DisplayName>
        <Value>0x4</Value>
    </EnumEntry>
    <EnumEntry Name="Line0">
        <DisplayName>Line Trigger 0</DisplayName>
        <pIsImplemented>DIN1ConnectorType</pIsImplemented>
        <Value>0x8</Value>
    </EnumEntry>
    <EnumEntry Name="Line1">
        <DisplayName>Line Trigger 1</DisplayName>
        <pIsImplemented>DIN1ConnectorType</pIsImplemented>
        <Value>0x9</Value>
    </EnumEntry>
    <pValue>TriggerSourceReg</pValue>
</Enumeration>

2.1 How Host IP Sends CXPTrigger

Excerpted from IP core manual.

2.1.1 Trigger Interface Description

The trigger interface supports mutual trigger transmission between Device and Host. Currently, no mainstream vendor supports Device-to-Host trigger transmission. Camera trigger sources are categorized into three types:

• CoaXPress Software Trigger: Implemented by Host writing registers to Device.
• CoaXPress Protocol Trigger: Trigger input through Host Link layer; better real-time performance than software trigger, widely used without extra physical trigger wiring.
• CoaXPress External Hardware Trigger: Controlled by external hardware wiring; lowest latency and negligible delay, but requires additional trigger signal cables.

This section describes the Host IP Link layer interface for sending trigger signals to CoaXPress Device.

Table 21 Trigger Interface Signals

Figure 21 Uplink Trigger Timing (Host to Device)

Figure 22 Downlink Trigger Timing (Device to Host)

2.2 How Device IP Receives CXPTrigger

Excerpted from IP core manual.

2.2.1 Trigger Interface Description

The interface supports trigger transceiving between Device and Host. Device-to-Host trigger is currently unsupported by most vendors.

Table 22 Trigger Interface Signals

Downlink Trigger (Device → Host): Not recommended and unsupported by most vendors.

To transmit downlink trigger, set trigger_in to select LinkTrigger index. Assert a single-cycle pulse on trigger_in_chg to start trigger packet transmission. The IP internally calculates and inserts trigger delay into the packet.

After downlink packet transmission, Host replies with acknowledge via I/O channel and generates a single-cycle pulse on trigger_ack. Do not issue a new trigger until the previous trigger is acknowledged or internal timeout expires.

Figure 23 Downlink Trigger Timing (Device to Host)

Uplink Trigger (Host → Device)

Upon receiving an uplink trigger packet, the IP outputs trigger level and delay value on trigger_out and trigger_delay_out respectively. A single-cycle high pulse on trigger_out_chg indicates valid trigger arrival. The IP automatically generates a reply command to Host.

Figure 24 Uplink Trigger Timing (Host to Device)