SMC-Based Digitizers Acquisition Engine State Diagram

The following figure shows the acquisition engine state diagram for SMC-Based digitizers.

NI SMC-based digitizers can be in any of the following basic states during the course of operation.

Idle—The module is not sampling a waveform. All the session attributes can be programmed in this state. In this state, the attributes have not necessarily been applied to hardware yet, so the hardware configuration of the module may not match the session attribute values. Also, the module remains configured as it was the last time a session was committed. When initiate is called on the module, all the attributes are programmed to the hardware. If the computer has just been reset, or niScope_ResetDevice has just been called, the module is in the Idle state.

Wait for Start Trigger—On initiating an acquisition, the module transitions to this state. If the Start (Acquisition Arm) Trigger Source is configured to Immediate, the module immediately transitions out of this state and generates a Start Trigger Event. If the Start Trigger Source has been configured for software or hardware trigger from one of the available sources, the module remains in this state until the configured trigger occurs. When the module recognizes a trigger condition, it transitions out of this state on the next clock cycle and generates a Start Trigger Event. The default Start Trigger Source is Immediate.

Minimum Pre-Reference Trigger Sampling—The module can transition into this state two ways: receiving the Start (Acquisition Arm) Trigger from the Start (Acquisition Arm) Trigger Source or receiving the Advance Trigger from the Advance Trigger Source. Transitioning into this state depends on the previous state of the module. While in this state, the module samples according to the session attributes configured. The module remains in this state until three conditions are satisfied: the minimum Pre-Reference Trigger sampling completes, the TDC is ready, and the trigger-to-trigger holdoff count has expired. The minimum Pre-Reference Trigger sampling is at least the user-configured Minimum Record Length multiplied by the user-configured Reference Position. The first time through this state, the trigger-to-trigger holdoff does not have an effect. When the three conditions have been satisfied, the module transitions out of this state on the next clock cycle.

Wait for Arm Reference Trigger while Sampling—After the module finishes the Minimum Pre-Reference Trigger Sampling state, the module transitions into this state. While in this state, the module continues to acquire Pre-Reference Trigger samples according to the session attributes configured. If the Arm Reference Trigger Source is configured to Immediate, the module transitions out of this state on the next clock edge. If the Arm Reference Trigger Source has been configured for a software trigger or a hardware trigger from one of the available sources, the module remains in this state until the configured trigger occurs. When the module recognizes a trigger condition, the module transitions out of this state. The default Arm Reference Trigger Source is Immediate.

Wait for Reference Trigger while Sampling—After the module receives Arm Reference Trigger from the Arm Reference Trigger Source, the module transitions into this state. If the Reference Trigger Source has been configured for a software or hardware trigger from one of the available sources, the module remains in this state until the configured trigger occurs. When the module recognizes a trigger condition, the module transitions out of this state. The default Reference Trigger Source is Immediate.

Post-Reference Trigger Sampling—After the module receives the Reference (Stop) Trigger, the module transitions into this state. At the beginning of this state, the module starts a trigger-to-trigger holdoff counter. This holdoff counter corresponds to the user-configurable Trigger Holdoff attribute and is used in the Minimum Pre-Reference Trigger Sampling State. You can use the Trigger Holdoff attribute to delay the module from looking for a Reference Trigger between records. At the same time, the trigger-to-trigger holdoff counter is started, the module begins sampling Post-Reference Trigger samples according to the session attributes configured. When the Post-Reference Trigger sampling is completed, the module transitions out of this state.

Record Complete—After the module completes Post-Reference Trigger sampling, the module transitions into this state. The module leaves this state after the current record has been stored in the onboard memory. Upon leaving this state, the module outputs an End of Record Event.

Wait for Advance Trigger—After the module has completed a record and determines that there are still more records to complete, the module transitions into this state. If the Advance Trigger Source is configured to immediate, the module transitions out of this state on the next clock edge. If the Advance Trigger Source has been configured for software or hardware trigger from one of the available sources, the module remains in this state until the configured trigger occurs. Upon the module recognizing a trigger condition, the module transitions out of this state. The default Advance Trigger Source is Immediate.

Done—After the module completes a record and determines that all the records are done, it transitions into this state. Upon entering this state, the module outputs the End of Acquisition Event, which is a temporary state. The software transitions the module out of this state and back to the Idle state when you call either Fetch or Check Status.