2049CH05 - Bitter Rick et al"Drivers" LabVIEW Advanced Programming Techinques Boca Raton CRC Press LLC,2001 5 ©2001 CRC Press LLC Drivers

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Unformatted text preview: Bitter, Rick et al "Drivers" LabVIEW Advanced Programming Techinques Boca Raton: CRC Press LLC,2001 5 ©2001 CRC Press LLC Drivers This chapter discusses LabVIEW drivers. A driver is the bottom level in the three- tiered approach to software development; however, it is possibly the most important. If drivers are used and written properly, the user will benefit through readability, code reuse, and application speed. LabVIEW drivers are designed to allow a programmer to direct an instrument, process, or control. The main purpose of a driver is to abstract the underlying low- level code. This allows someone to instruct an instrument to perform a task without having to know the actual instrument command or how the instrument communi- cates. The end user writing a test VI does not have to know the syntax to talk to an instrument, but only has to be able to wire the proper inputs to the instrument driver. The following sections will discuss some of the common communication meth- ods that LabVIEW supports for accessing instruments and controls. After the dis- cussion of communication standards, we will go on to discuss classifications, inputs and outputs, error detection, development suggestions, and, finally, code reuse. The standard LabVIEW driver will be discussed first. This standard driver is the basis for most current LabVIEW applications. In an effort to improve application performance and flexibility, a new style of driver has been introduced. The Inter- changeable Virtual Instrument (IVI) driver is a new driver technology and will be described in depth later in this chapter. 5.1 COMMUNICATION STANDARDS There are many ways in which communications are performed every day. Commu- nication is a method of sharing information. People can share information with each other by talking, writing messages, sign language, etc. Just as people have many different ways to communicate with each other, software applications have many ways to communicate with outside entities. Programs can talk to each other, to instruments, or to other computers. The following communication standards are just some of the methods LabVIEW uses to communicate with the outside world. 5.1.1 GPIB The General Purpose Interface Bus (GPIB) is a standard method of communication between a computer/controller and test equipment. The GPIB consists of 16 signal lines and 8 ground return lines. The 16 signal lines are made up of 8 data lines, 5 control lines, and 3 handshake lines. The GPIB interface was adopted as a standard (IEEE 488). The maximum GPIB data transfer rate is about 1Mbyte/sec. A later ©2001 CRC Press LLC version of the standard with added features was defined in 1987. This standard is the ANSI/IEEE 488.2. This enhancement to the standard defines how the controller should manage the bus. The new standard includes definitions of standard messages for all compliant instruments, a method for reporting errors and other status infor- mation, and the protocols used to discover and configure GPIB 488.2 instrumentsmation, and the protocols used to discover and configure GPIB 488....
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This note was uploaded on 03/11/2010 for the course MECHANICAL 1234 taught by Professor Futao during the Spring '10 term at Kasetsart University.

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2049CH05 - Bitter Rick et al"Drivers" LabVIEW Advanced Programming Techinques Boca Raton CRC Press LLC,2001 5 ©2001 CRC Press LLC Drivers

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