Chapter 16: LabVIEW and Serial Interfaces

Chapter 16: LabVIEW and Serial Interfaces

George Wells

Measurement Technology Center (MTC), Jet Propulsion Laboratory, California Institute of Technology

Overview

This chapter is about using serial ports to interface with various data acquisition devices and controllers collectively called serial instruments . ¹ Virtually all computers have serial ports intended for connection to modems or printers and, as such, have excellent operating system support. Despite the simplicity of this interface (there are only five basic serial functions and VIs in LabVIEW), many people are confused about how to hook serial ports up, so we begin with a description of the hardware layer.


	1	It is not about using the serial ports with SCXI, for which everything will be taken care of for you if you simply run NI-DAQ. FieldPoint also has its own software.

RS-232

The usual specification for serial ports is RS-, although this standard is rarely fully complied with. Our interest is in understanding how to successfully connect a computer to a device that claims to be RS-232 compatible, even if both the computer and the device are not in full compliance with the standard. The standard is written from the point of view of connecting a computer to a modem (Fig. 16.1). This means that all the terminology for the two data lines and the six handshaking lines (Tables 16.1 and 16.2) assumes that a modem is being used, which is generally not the case with serial instruments.

Figure 16.1: The original concept for RS-:...

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