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You then want the Initialize message diagram to send the Acquire Data message to the same MHL. You want to add a button that sends the Initialize message to the data acquisition MHL. You can send a message from a front panel control or from a message diagram. Therefore, you need to determine when to send each message to the MHL. A message diagram executes after its MHL receives the appropriate message. You need to determine when to execute each message diagram. The Initialize message diagram needs to open this reference, the Acquire Data diagram uses this reference to acquire data, and the Exit message diagram closes the reference.ĭefining Data that a Message Handling Loop Needs section in Create a Message Diagram in LabVIEW Queued Message Handler Template You must determine what data the message diagrams of an MHL need.Įach message diagram of the data acquisition MHL needs access to a hardware reference. Therefore, create these message diagrams in the MHL that logs data.Ĭreate a Message Diagram in LabVIEW Queued Message Handler Template You want to separate the data logging task into three states: Initialize, Log, and Close. Therefore, create these message diagrams in the MHL that acquires data. You want to separate the data acquisition task into three states: Initialize, Acquire Data, and Exit. Each subdiagram corresponds to a state the task can be in therefore, to determine the message diagrams to add, separate each task into states. Therefore, you need two Message Handling Loops.Ĭreate a Message Handling Loop in LabVIEW Queued Message Handler Templateįor each MHL, you need to determine what message diagrams to add.Ī message diagram is a subdiagram of the Case structure in an MHL. This application consists of two tasks: data acquisition and data logging. You have an application that acquires data and, in parallel, logs this data to disk. Each MHL defines a task that executes in parallel with other tasks. You need to determine how many MHLs to add. In this template, the cluster is defined as a typedef, UI Data.ctl. This cluster is data that each message diagram in an MHL can access and modify. Notice the UI Data cluster in the above diagram.Each MHL corresponds to a task the application performs, such as acquiring or logging data. Your application can have multiple MHLs.Although the MHL primarily consumes messages, it also can produce them. Every iteration of the MHL reads the oldest message in the message queue and then executes the corresponding message diagram.Each message queue belongs to a single MHL. Because the EHL sends messages to this queue and not directly to the MHL, the EHL can produce messages while the MHL is not consuming them. The message queue is a LabVIEW queue that stores messages for consumption.These loops run in parallel and are connected by the message queue, which facilitates communication between the loops. Optionally, the message diagram produces another message, storing it in the message queue.This subdiagram is called a message diagram because it corresponds to a message. Therefore, reading the message causes the corresponding subdiagram of the Case structure to execute. The message is a string that matches one of the subdiagrams of the Case structure in the MHL.The Message Handling Loop (MHL) reads a message from the message queue, removing the message.A user interacts with the front panel, causing the Event structure in the Event Handling Loop (EHL) to produce a message.
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This template repeatedly executes the following steps: The QMH template provides a starting point for writing this kind of application. Therefore, the application requires a third parallel loop that continuously monitors the front panel for events, such as the following commands: The application requires a responsive user interface that is, users should be able to click buttons even while the application is executing another command.
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These signals occur at different rates, so the application must have two loops that run in parallel. For example, consider an application that continuously acquires, logs, and displays two signals: an RS-232 signal and an analog signal. The QMH template is useful for applications where multiple tasks occur in parallel, often at different rates.