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Floyd, Digital Fundamentals, 10 th ed EET 2259 Unit 14 Instrument Control Read Bishop, Appendix A. Homework #14 due next week.

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Presentation on theme: "Floyd, Digital Fundamentals, 10 th ed EET 2259 Unit 14 Instrument Control Read Bishop, Appendix A. Homework #14 due next week."— Presentation transcript:

1 Floyd, Digital Fundamentals, 10 th ed EET 2259 Unit 14 Instrument Control Read Bishop, Appendix A. Homework #14 due next week.

2 Floyd, Digital Fundamentals, 10 th ed Instrument Control You can use LabVIEW to control instruments (multimeters, oscilloscopes, etc.) if your computer and the instrument have ports that let them talk to each other. Two ports commonly used for instrument control are: RS-232 port (the serial port found on many computers) GPIB port (General Purpose Interface Bus)

3 There are dozens of bus standards in common use. From Wikipedias article on the USB bus: Many Bus Standards

4 Some bus standards apply to serial communication (1 data bit transferred at a time). Others apply to parallel communication (several data bitsusually 8transferred at a time). Terminology: Serial vs. Parallel

5 These are two common measures of speed in communications. Many writers loosely treat these as being synonyms, but this is not strictly correct. Bits per second (bps) is the easier to understand. Often expressed as kbps or Mbps. In the simplest cases, baud rate equals bps. In more sophisticated schemes, the two are related but not equal. Traditional baud rates are 300, 600, 1200, 2400, 4800, 9600, Terminology: Bits per Second and Baud Rate

6 First version created in early 1960s. Obsolete in some respects, but still very widely used. Many PCs have one or two RS-232 ports, although theyre becoming less common as USB becomes more popular. In recent years, has been applied in ways that its original creators never imagined, sometimes leading to problems. Original spec defined 25 lines, but often only 9 or fewer are used. RS-232 Standard

7 In any RS-232 application, each device is designated as either Data Terminal Equipment (DTE) or Data Communications Equipment (DCE). Simple case: When you connect a personal computer to a modem, the computer is the DTE and the modem is the DCE. Terminology: DCE vs DTE

8 Original RS-232 standard called for a DB-25 connector. Since many later applications didnt use most of the pins, it became common to use DE-9 connectors (often mistakenly referred to as DB-9). Connectors

9 The nine most important signals: RS-232 Signals DescriptionAbbrev.Direction DTE - DCE DB-25 Pin # DE-9 Pin # Transmitted dataTxD 23 Received dataRxD 32 Request to sendRTS 47 Clear to sendCTS 58 Signal Ground75 Protective Ground1 Data set ReadyDSR 66 Data carrier detectDCD 81 Data terminal readyDTR 204

10 The four handshaking signals defined in RS- 232 are: Request to Send (RTS) Clear to Send (CTS) Data Terminal Ready (DTR) Data Set Ready (DSR) RS-232 Handshaking

11 Roughly speaking, TTL voltage levels are: 0 V for a binary 0 +5 V for a binary 1. This scheme is unipolar because it doesnt use negative voltages. For transmission over a cable, its undesirable to have either logic level close to 0 V. RS-232 uses a bipolar scheme, with: +3 V to +25 V for a binary 0 (space) -3 V to -25 V for a binary 1 (mark) RS-232 Voltage Levels

12 While RS-232 is still widely used, it has many technical limitations. The most obvious are: Maximum speed: 20 kbaud Maximum cable length: 50 feet Point-to-point communication: just two users communicating Limitations of RS-232

13 Original PC Printer Port (Centronix Port) IEEE 488 (GPIB) SCSI (Small Computer System Interface) Some Parallel Bus Standards

14 GPIB = General Purpose Interface Bus Formerly known as HPIB (Hewlett-Packard Interface Bus) First version created in late 1960s. Primarily used to connect test equipment (power supplies, function generators, multimeters, oscilloscopes, etc.) and let them be controlled by a computer. IEEE 488 Standard (GPIB)

15 In any GPIB application there must be one (and only one) controller. There can also be up to 14 other devices, which are categorized as talkers, listeners, or talker/listeners. Each device must be assigned a unique address within the network. GPIB Controller, Talker, & Listener

16 The GPIB standard calls for a 24-pin connector: 8 data lines 8 ground lines 8 control lines (= 3 handshake lines and 5 bus-management lines) GPIB Connectors

17 The 3 handshake lines: The 5 bus management lines: GPIB Control Lines DescriptionAbbrev.Originates from Data validDAVTalker Not ready for dataNRFDListener Not data acceptedNDACListener DescriptionAbbrev.Originates from Interface clearIFCController AttentionATNController Remote enableRENController Service requestSRQAny device End or identifyEOITalker

18 Ports on our Fluke 45 DMMs RS-232 (Serial) IEEE 488 (GPIB) option not installed (Parallel)

19 Ports on our Tektronix TDS2014s RS-232 (Serial) IEEE 488 (GPIB) (Parallel) Printer (Parallel)

20 Without LabVIEW, its still possible to establish communications between a computer and an instrument with an appropriate port. Free software such as Windows Hyperterminal lets you communicate with any device connected to the computers RS-232 port. Instrument Control without LabVIEW

21 1. Connect serial cable. 2. Meter setup: 2 nd Rate, 9600, n, on. 3. Connect meters leads to func gen set for half-max amplitude & 5 kHz. 4. Hyperterminal setup: COM1, 9600, 8, N, 1, XON/XOFF. 5. Commands: *IDN? VAC FREQ2 VAL? Using Hyperterminal with a Fluke 45 Multimeter

22 1. Connect serial cable. 2. Scope setup: Utility> Options> RS232> 19200, Hard, LF/CR, None. 3. Connect probe to compensation terminal. 4. Hyperterminal setup: COM1, 19200, 8, N, 1, HARDWARE. 5. Use Notepad to create text file: *IDN? Autoset execute measurement:immed:source ch1 measurement:immed:type pk2 measurement:immed:value? 6. Save file & send it from Hypterminal using Transfer > Send Text File. Using Hyperterminal with a Tektronix TDS2014 Oscilloscope

23 LabVIEW gives you a few different ways to control instruments: 1.Using the same low-level commands that weve been using in Hyperterminal. 2.Using an Instrument Driver, which typically is written by an employee of the company that manufactured the instrument. 3.Using the Instrument I/O Assistant. Option #2 is usually the best and easiest way to go, assuming that an Instrument Driver is available. Instrument Control Using LabVIEW

24 Within LabVIEWs Instrument I/O palette are several sub-palettes, including the Serial sub-palette. This contains functions that let you send the same commands weve been entering in Hypterterminal. Option #1: Using Low-Level Commands

25 NIs website contains Instrument Drivers for thousands of instruments manufactured by dozens of companies: A typical instrument driver consists of one or more llb (LabVIEW library) files containing VIs to designed to control a specific device. Usually one of these VIs is named Getting Started, and you should start with that one. Option #2: Using an Instrument Driver

26 Example: Instrument Driver for Fluke 45

27 If you cant find an Instrument Driver for your instrument, LabVIEWs Instrument I/O Assistant provides a wizard-type dialog box to help you configure and control your device. Option #3: Using the Instrument I/O Assistant

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