Hardware Triggering

Overview

The Alta and Ascent camera systems allow for the use of an external, hardware trigger/signal to begin an exposure. The trigger signal arrives through the camera I/O port the pins and use of which are defined in another section of this document. This section provides additional detail on the properties for enabling or disabling different types of exposure triggers.

Previous versions of the driver and firmware used the CameraMode property to control hardware triggering, by setting this property to either Apg::CameraMode_ExternalShutter or Apg::CameraMode_ExternalTrigger. Trigger operations are now controlled by properties that are set when using the camera in a specific mode. The following short table shows the trigger properties and the corresponding camera modes for which they are valid.

Mode	Type	Normal	TDI	Kinetics
Apg::TriggerMode_ExternalShutter	Apg::TriggerType_Each or Apg::TriggerType_Group	Yes	No	No
Apg::TriggerMode_ExternalReadoutIo	Apg::TriggerType_Each or Apg::TriggerType_Group	Yes	No	No
Apg::TriggerMode_Normal	Apg::TriggerType_Each or Apg::TriggerType_Group	Yes	No	No
Apg::TriggerMode_TdiKinetics	Apg::TriggerType_Each or Apg::TriggerType_Group	No	Yes	Yes

The ExternalShutter property is straightforward. When used, this signal (which is assigned a different I/O pin than the usual trigger start signal) controls the length of the exposure. It may be used in conjunction with the ExternalIoReadout property, to control when digitization begins. These two properties are designed to be used with single exposures.

The Each/Group trigger properties are designed to give the greatest flexibility and number of options to users, for each corresponding camera mode.

Normal Mode Triggers

The following chart details how the Each/Group type for the Apg::TriggerMode_Normal mode are interpreted when ImageCount equals one (single exposure) and when ImageCount is greater than one (using the camera's internal sequence engine).

Apg::TriggerType_Each State	Apg::TriggerType_Group State	ImageCount = 1	ImageCount > 1
FALSE	FALSE	Software initiated single exposure. No hardware trigger enabled.	Software initiated sequenced exposure. No hardware trigger enabled.
FALSE	TRUE	Hardware trigger is used to begin the single exposure.	Hardware trigger is used to begin the sequenced exposure. One trigger kicks off the entire series of images.
TRUE	FALSE	Not a valid/usable option, and will have no impact. Because ImageCount is one, the camera control firmware should ignore the Each setting.	The first image of the sequence is begun by software control. Each subsequent image in the sequence will be initiated when its corresponding hardware trigger arrives.
TRUE	TRUE	Hardware trigger is used to begin the single exposure. Because ImageCount is one, the camera control firmware should ignore the Each setting.	The first image, as well as all subsequent images, of the sequence will be initiated by a corresponding hardware trigger.

TDI-Kinetrics Triggers

The following chart details how the Each/Group types are interpreted for the Apg::TriggerMode_TdiKinetics. TDI operation presumes multiple rows, are in effect a sequence of normal images. Kinetics operation presumes multiple sections, are in effect a sequence of normal images.

Apg::TriggerType_Each State	Apg::TriggerType_Group State	Description
FALSE	FALSE	Software initiated imaging No hardware trigger enabled.
FALSE	TRUE	A single hardware trigger is used to begin the entire TDI or Kinetics image.
TRUE	FALSE	The first row/section of the TDI/Kinetics image is begun by software control. Each subsequent row/section in the TDI/Kinetics image will be initiated when its corresponding hardware trigger arrives.
TRUE	TRUE	The first and subsequent rows/sections of the TDI/Kinetics image will be initiated by a corresponding hardware trigger.

Control and Usage