Each time you read from an I/O variable using scanned access, the NI Scan Engine immediately returns the most recent value stored in the memory map without blocking, or waiting for a new value. During each scan, LabVIEW reads the most recent I/O value and writes that value to the NI Scan Engine memory map.
Each time you write to an I/O variable using scanned access, you overwrite the previous value stored in the scan engine memory map. During each scan, LabVIEW pushes the value stored in the memory map to the physical I/O channel. To prevent data loss, you must synchronize all I/O variable write operations to the scan period.Direct Access:Use direct access to read or write single-point local I/O channels asynchronously to the scan period. You can use direct access when the application needs to write a value as soon as possible. Direct access bypasses the scan engine memory map and communicates directly with the I/O device driver to perform non-blocking I/O reads and writes, as shown in the following figure:
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